The Ultimate Guide: House Bulbs, LEDs & Grow Lights
Supplemental Plant Lighting 101💡
One of the most difficult aspects of keeping plants indoors is providing the right levels of lighting. When window lights aren't good enough for plant growth, a growth lamp may be essential. There are lots of reasons why people use grow lights indoors; for winter supplementation, for houses without full sun windows, or to help keep plants in darker corners. Grow lights can even be used to help rare, expensive, or sickly plants.
People often get overwhelmed when they hear the term “grow lights”. They can seem expensive, complicated, and too big to have in your home. The good news is that you don't need to have a commercial grow light setup to achieve plant growth indoors. Some high-powered regular house bulbs provide a good baseline for plant growth, and when supplemented with additional lighting, you can provide an environment more suitable to achieve mature plant growth, fenestrations and mature colouration.
Stay tuned as we dive into the entire world of plant lighting, starting with regular house bulbs to help plants grow indoors. We explore the benefits of LED lights, then we visit the world of full spectrum grow lights, which closely mimic the sun's natural light. We cover which brands to buy, what wattage you need for your houseplants, where to put them, and how to troubleshoot issues that you may face with artificial lighting for indoor plants.
Does A Normal Ceiling Light Give Enough Light For Plants?
If you're wondering if any light bulb can be used as a grow light, then the answer would be, in theory, yes. The higher the lumen output on your light, the more growth you will see from your plant. This doesn't factor in light spectrum, which we will discuss later in much more detail, as it has a direct impact on how your plants grow indoors. For now, let's explore what can be used as a grow light:
Natural Sunlight: Place your sun loving houseplants near south-facing windows to maximize exposure to natural light. This is often the best and simplest solution if you have suitable windows available in your home. If you don't have any good sun windows, grow lights can be the next best option to help your houseplants grow.
Bright Fluorescent Bulbs: While not as effective as grow lights, high-output fluorescent bulbs can provide a decent amount of light. They're better suited for low-light plants like Spider Plants.
LED Lamps: Some high-powered LED lamps can be adjusted to provide focused light and offer a good alternative to grow lights. This is one of the methods that we use ourselves in the office, we highly recommend utilizing LED lamps.
LED Ceiling Lamps: In our office, we use high output LEDs in our ceiling fixtures to provide additional lighting to our houseplants. This is one of our best tips for increasing artificial lighting, as they up the base lumen output in every room.
Reflective Surfaces: Use mirrors or reflective panels to amplify the available light and distribute it more evenly around your plants. A cleverly positioned mirror opposite a sunny window will reflect that light around the room, sharing it with more of your houseplants.
Bulbs with High Lumen Output: The high-powered house bulbs that we recommend can offer more light intensity than standard bulbs, but be cautious of heat. A great rule of thumb is that if it's too hot for your hand to be near the plant after a few seconds, then it's too hot for your plant.
We're frequently asked if you can turn a regular lamp into a grow light. You absolutely can, simply by changing your light bulb for a high output bulb. Always check the maximum wattage of your light fixture and never exceed that rating, or your lamp will blow a fuse, and potentially break your high-powered bulb. Never use dimming switches with non dimming bulbs, as that will also wreck a bulb!
What Colour Light Bulb Helps Plants Grow?
For houseplants, the best colour light bulb to help them grow is one that provides a full spectrum or daylight white, typically labelled as 5000K to 6500K on the bulb's packaging. Check with your light bulb manufacturer if you no longer have the packaging. Here's how different Kelvin ratings impact plant growth:
Kelvin Ratings and Houseplant Growth
Warm White (2700K-3000K): Emits a warm, yellowish light, similar to traditional tungsten bulbs.
Effect on Houseplants: Contains more red wavelengths, which can be beneficial for flowering houseplants like Hoya, Lillie's, African violets or orchids. However, it may not be ideal for foliage plants that require more blue light for leafy growth.Cool White/Neutral White (3500K-4100K): Produces a balanced light with both blue and red wavelengths.
Effect on Houseplants: Suitable for general houseplant growth, providing a mix of wavelengths that support both leafy and flowering stages. This balance makes it a good option for mixed plant collections.Daylight (5000K-6500K): Mimics natural daylight with a bright, white light that includes a full spectrum.
Effect on Houseplants: Ideal for most houseplants, particularly those that thrive in bright, indirect light, such as Monstera, Pothos, and Philodendrons. The high blue light content promotes strong, healthy foliage growth, and it also provides enough red light to support flowering in many houseplants.
What Can I Use Instead Of A Grow Light?
How Many Hours Of Artificial Light For Plants?
Here's a comparison of the recommended hours of artificial light per day for houseplants using different light sources:
How Many Hours Of House Bulbs
House bulbs should typically be used for 12–14 hours a day. These bulbs provide moderate light intensity and are suitable for general indoor plant growth.
How Many Hours Of Grow Lights
Grow lights are designed to mimic natural sunlight and provide a full spectrum of light. They are best used for 14–18 hours a day to support robust plant growth, especially for plants that require more light.
How Many Hours Of Fluorescent Light
Fluorescent lights, such as T5 High Output tubes, T8 tubes and compact fluorescent lights (CFL) are ideal for indoor gardening. They provide a balanced spectrum and should be used for 12–16 hours a day.
How Many Hours Of Window Light
Natural sunlight through a window is the best source of light for plants. Depending on the location and time of year, window light can provide an average of 6–8 hours of light per day. South-facing windows are ideal for maximum light exposure.
Full Sun Houseplants: Sun lovers need at least 6–8 hours of direct sunlight daily (e.g., Ficus).
Bright Indirect Light Houseplants: They thrive with indirect light and 1–2 hours of sun (e.g., Monstera).
Medium Light Houseplants: These require 2–4 hours of direct sun, plus indirect light (e.g., Orchids).
Low Light Houseplants: These do well with little to no direct sunlight (e.g., Sanseveria, ZZ).
You may remember a time when the idea of using LEDs to grow plants was laughable, however, times have changed. Modern day LEDs are highly efficient, long-lasting, and are usually designed to provide the full spectrum of light for growing plants indoors. Despite common misconceptions, LED grow lights are not all expensive or bulky any more. As technology advances, LED grow lights get more efficient. Because of improvements in LED technology, they now output more light, are more affordable to manufacture, and they run cooler, which is safer for houseplants. We have now reached a point in technology where LED lights are suitable for indoor plants.
Can LED Lights Really Help Plants Grow?
How Many Hours Of Artificial Light For Plants?
Here's a comparison of the recommended hours of artificial light per day for houseplants using different light sources:
How Many Hours Of House Bulbs
House bulbs should typically be used for 12–14 hours a day. These bulbs provide moderate light intensity and are suitable for general indoor plant growth.
How Many Hours Of Grow Lights
Grow lights are designed to mimic natural sunlight and provide a full spectrum of light. They are best used for 14–18 hours a day to support robust plant growth, especially for plants that require more light.
How Many Hours Of Fluorescent Light
Fluorescent lights, such as T5 High Output tubes, are ideal for indoor gardening. They provide a balanced spectrum and should be used for 12–16 hours a day.
How Many Hours Of Window Light
Natural sunlight through a window is the best source of light for plants. Depending on the location and time of year, window light can provide an average of 6–8 hours of light per day. South-facing windows are ideal for maximum light exposure.
Full Sun Houseplants: Sun lovers need at least 6–8 hours of direct sunlight daily (e.g., Ficus).
Bright Indirect Light Houseplants: They thrive with indirect light and 1–2 hours of sun (e.g., Monstera).
Medium Light Houseplants: These require 2–4 hours of direct sun, plus indirect light (e.g., Orchids).
Low Light Houseplants: These do well with little to no direct sunlight (e.g., Sanseveria, ZZ).
What Happens When Plants Don't Get Enough Light?
When plants don't receive enough light, several issues can arise, affecting their overall health and growth. Here are some common problems:
Stunted Growth: Without sufficient light, plants can't produce enough energy through photosynthesis, leading to slow or halted growth. They may remain small and fail to develop properly.
Leggy Stems: Plants will stretch toward any available light source, resulting in long, weak, and spindly stems. This is known as etiolation and can make the plant less stable and more prone to breakage.
Pale or Yellowing Leaves: Insufficient light can cause chlorosis, where the leaves lose their green colour and turn pale or yellow. This happens because the plant cannot produce enough chlorophyll.
Poor Flowering and Fruiting: For flowering and fruiting plants, inadequate light can lead to reduced or absent blooms and fruits. The plant prioritizes survival over reproduction when light is scarce.
Drooping or Wilting: Lack of light can weaken a plant's overall structure, causing leaves and stems to droop or wilt. This is due to the plant's inability to maintain turgor pressure without adequate energy.
Leaf Drop: Some plants may shed leaves as a survival mechanism when light is insufficient. This helps reduce energy expenditure and conserve resources.
Increased Vulnerability to Pests and Diseases: Weakened plants are more susceptible to pests and diseases, as their natural defences are compromised.
To help plants thrive, it's essential to provide adequate light based on their species. Adjusting the position of artificial lights, using grow lights, or moving plants to brighter locations can significantly improve their health and growth.
How Does Light Colour Effect Plant Growth?
Different colours of the light spectrum can have different effects on plants. Light colour is often used by commercial houseplant growers to modify a plant's growth in desirable ways. Different colours of light can even be used to control plant growth, preventing them from getting too tall or leggy before transportation or sale. Here's how different light colours, including UV, affect plant height, overall size, internodal distances, and flower production in houseplants:
UV Light (0-400 nm)
Effect on Height: Can cause plants to grow shorter and more compact.
Internodal Distance: Reduces internodal distances, making plants more dense.
Flower Production: Enhances plant protective compounds, but too much can be harmful.
Reason: UV forces plants to make protective compounds, leading to thicker leaves and stems.
Blue Light (400-500 nm)
Effect on Height: Promotes shorter, stockier plants.
Internodal Distance: Reduces internodal distances, leading to more compact growth.
Flower Production: Supports vegetative growth rather than flower production.
Reason: Enhances the production of chlorophyll, crucial for photosynthesis and dense foliage.
Green Light (500-600 nm)
Effect on Height: Minimal impact on height.
Internodal Distance: Does not significantly affect internodal distances.
Flower Production: Less effective for stimulating flowers.
Reason: Penetrates deeper into the canopy, helping lower leaves receive some light.
Red Light (600-700 nm)
Effect on Height: Can lead to taller plants.
Internodal Distance: Increases internodal distances, resulting in longer stems.
Flower Production: Highly effective for increasing flower production.
Reason: Stimulates the growth hormone responsible for cell elongation and flowering.
Far-Red Light (700-800 nm)
Effect on Height: Encourages taller growth.
Internodal Distance: Significantly increases internodal distances.
Flower Production: Can promote flowering but should be used in combination with red light.
Reason: Signals the plant to grow upwards and can manipulate flowering times.
Full Spectrum Light
Effect on Height: Provides balanced growth, resulting in typical plant height.
Internodal Distance: Maintains typical internodal distances.
Flower Production: Supports all stages of growth, including flowering.
Reason: Includes a mix of blue, red, and other wavelengths, supporting overall plant health.
How To Choose The Right Wattage Grow Light
For houseplants, choosing the right wattage for grow lights depends on these key factors:
Plant Type: Houseplants like ferns and Epipremnum require less light compared to high-light plants like succulents and flowering houseplants. Plants like Monstera need more light to achieve mature fenestrations, colouration, and holes.
Growth Stage: Young plants and seedlings require less intense light, whereas mature plants require more light to thrive.
Growing Area: Measure the space to ensure even light distribution.
General Wattage Guidelines:
10–20 watts per square foot: for low-light plants
20–30 watts per square foot: for medium-light plants
30–40 watts per square foot: for high-light plants
How To Convert Any House Lamp Into A Grow Light
When it comes to changing your regular house bulbs for higher powered bulbs, there are a few brands that stand out amongst the competition for indoor plant growth. In our office, we exclusively use the same Philips bulbs that we've listed below. We use these in hanging lamps around our houseplants to give us artificial light suitable for indoor plant growth. We've had great experience growing houseplants in total darkness by using these high-powered bulbs, and we highly recommend them. By swapping your regular house bulbs for high-powered LEDs, you can provide more direct light for your plants, and turn any lamp into a grow light. Let's dive in to the list:
Brand: Philips house bulb — Our personal favourite!
Type: e27 bulb
Equivalent Wattage: 150w
Actual Wattage: 36w
Lumens: 2452lm
Spectrum: N/A
Kelvin: 2700k
Price: £9.99
Purchase Link: Amazon
Brand: Sansi house bulb
Type: e27 bulb
Equivalent Wattage: 400w
Actual Wattage: 36w
Lumens: 3250lm
Spectrum: 380 nm — 780 nm
Kelvin: 4000k
Price: £29.95
Purchase Link: Amazon
Brand: Sansi house bulb
Type: e27 bulb two pack
Equivalent Wattage: 200w
Actual Wattage: 15w
Lumens: 1350lm
Spectrum: 380 nm — 780 nm
Kelvin: 4000k
Price: £24.74
Purchase Link: Amazon
Brand: Pianta house bulb
Type: e27 bulb
Equivalent Wattage: N/A
Actual Wattage: 18w
Lumens: 2366lm
Spectrum: 380 nm — 780 nm
Kelvin: 3400k
Price: £35.00
Purchase Link: Amazon
You can grow plants with regular t5 or t8 fluorescent lights, although they may not be as effective as specialized grow lights. Fluorescent lights include CFL lights, T5 fluorescent tubes, T8 fluorescent lights, and specialized grow lights. Each have their advantages and considerations, let's explore them in more detail:
Pros of Using CFL and Regular Fluorescent Lights
Energy Efficiency: Fluorescent lights are more energy-efficient compared to older incandescent bulbs.
Low Heat Emission: Fluorescent lights produce less heat, reducing the risk of burning your plants.
Availability: These bulbs are readily available from shops and are relatively affordable to purchase.
Low-Light Plants: Fluorescent lights are perfect for plants that require less light (e.g., Spider Plants, Pothos).
Seedlings and Herbs: These lights are effective for starting seedlings, propagation, and for growing herbs.
Cons of Using Fluorescent Lights
Spectrum: May not provide the full spectrum of light. Doesn't provide red light, which is essential for flowering and fruiting.
Intensity: The light intensity may be lower than what is ideal for robust plant growth.
Tips for Using Fluorescent Lights for Plant Growth
Distance: Keep the lights close to the plants (within a few inches) but not so close that they cause heat damage.
Duration: Provide about 12–16 hours of light per day to mimic natural daylight. Provide a rest period at night.
Reflectors: Use reflectors or place plants in a reflective space to maximize light efficiency.
Where To Buy Fluorescent Grow Lights
Local hydroponic shops can carry a wide range of fluorescent lighting for houseplants, alternatively, you can find some on Amazon. A couple of lights worth mentioning are the Lumii 125w 6400k CFL grow light, which fits a standard e27 light fitment. You can also get generic 135w 5500k CFL and 250w CFL which would work for plant growth when distanced appropriately.
Can You Grow Plants With Regular Fluorescent Lights?
Best Full Spectrum LED Grow Lights For Houseplants
We've scoured the internet and made a list of LED lights for growing plants indoors. We've included some affordable options, some more professional LEDs and a range of fixtures and fittings. If you want to add your LED to this list for free, please get in touch and send us the specifications of your product. We are not sponsored by any of these brands, so these are genuine recommendations, not clickbait for hits on a page.
When it comes to grow lights, equivalent wattage refers to the amount of power the light consumes and how it compares to traditional lighting sources. For example, a 30-watt LED grow light might provide the same amount of light as a 150-watt incandescent bulb, so the manufacturer may list that bulb as a 150w grow light. The actual wattage used is much less than the equivalent, so we've included a section for this in our list.
Brand: Sansi
Type: Gooseneck unit
Equivalent Wattage: 300w
Actual Wattage: 20w
Lumens: 1800lm
Spectrum: 400 nm — 780 nm
Kelvin: 4000k
Price: £35.00
Purchase Link: Amazon
Brand: Mother
Type: Floor unit
Equivalent Wattage: N/A
Actual Wattage: 16w
Lumens: N/A
Spectrum: 380 nm — 780 nm
Kelvin: N/A
Price: £129.00
Purchase Link: Amazon
Brand: Mother
Type: Floor unit
Equivalent Wattage: N/A
Actual Wattage: 32w
Lumens: 2600lm
Spectrum: 380 nm — 780 nm
Kelvin: N/A
Price: £209.00
Purchase Link: Amazon
Brand: Root It!
Type: Hanging lamp
Equivalent Wattage: N/A
Actual Wattage: 26w
Lumens: N/A
Spectrum: N/A
Kelvin: 6500k
Price: £35.00
Purchase Link: Amazon
The simple answer is yes, however, plant growth depends on a few factors. In our experience, it is always best to use the highest watt LED grow light possible for your budget, as more power equals more light. The more lumens your LED bulbs are, the more light is available for photosynthesis to the houseplants. The next factor to consider is the distance between your plant and the LED light. We have great experience using hanging lamps with supplementary LED bulbs, as it allows us to position the LED very close to the plant to achieve maximum growth. You do have to be careful not to burn your plant leaves, a great rule of thumb that we use here at the shop is that if your hand is uncomfortable under the light, so is your plant. If you can't keep your fingers underneath the beam of the light for more than a few seconds, it's likely to burn your plant's leaves to a crisp. One of the best things about modern LED grow lights is that they run cool and can be placed extremely close to the leaves without scorching them. The final factor to consider is the colour of your LED, which is called kelvin. Daylight white, warm white and white LEDs are going to give you better plant growth than one that leans towards blue or green. Red is a very good colour for plants, so any warm colours are usually good, depending on the spectrum of the light itself.
Can You Grow Plants With LEDs Not Designed Specifically For Plants?
Can Too Much LED Light Hurt Plants?
Plants can get too much LED light, and it can severely harm plants. Here are a few potential issues:
Light Burn
Symptoms: Leaves can become scorched, showing brown or yellow spots. The edges of the leaves may curl or crisp up. Large areas may go brown and crispy, especially if variegated, like shown in the image.
Cause: Excessive light intensity or prolonged exposure can damage the plant tissues.
Stress
Symptoms: Stunted growth, wilting, or unusual colouration.
Cause: Constant intense light without periods of darkness can stress plants, disrupting their natural processes.
Heat Damage
Symptoms: Similar to light burn, but more localized to areas closest to the light source.
Cause: Even though LEDs produce less heat than other bulbs, high-intensity LEDs can still generate enough heat to harm plants if placed too close.
Nutrient Imbalance
Symptoms: Chlorosis (yellowing leaves), poor growth.
Cause: Excess light can increase the plant's metabolic rate, leading to a higher demand for water and nutrients, which might not be met.
Artificial Light Damage Prevention Tips
Distance: Maintain a proper distance between the lights and plants, adjusting as they grow.
Light Schedule: Provide periods of darkness to mimic natural day-night cycles, usually 14–16 hours of light and 8–10 hours of darkness.
Monitoring: Regularly check your plants for signs of light stress and adjust the lighting as needed.
How Far Should My LED Lights Be From My Plants?
The ideal distance for LED lights from houseplants varies depending on the type of plant and the intensity of the light. A good rule of thumb is to check the light intensity with your hand by placing it on the leaves between the plant and the bulb. If your fingers can't be near the plant, it's a good sign that the light is too close. Let's dive in:
High-Light Houseplants
Distance: 12–24 inches (30-60 cm)
Reason: These plants require less intense light, so keeping the LED lights closer ensures they get enough without overwhelming them.
Medium-Light Houseplants
Distance: 18–24 inches (45-60 cm)
Reason: These plants need moderate light, and this distance provides a good balance of intensity and coverage.
Low-Light Houseplants
Distance: 24–36 inches (60-90 cm)
Reason: These plants thrive in bright light, and placing the LEDs at this distance ensures they receive enough light for photosynthesis without causing stress.
Tips for All Houseplants
Adjustability: Use adjustable light fixtures to easily change the distance as your plants grow, like we do in our office and grow rooms.
Monitor Plants: Watch for signs of light stress (e.g., leaf burn or yellowing) and adjust the lights accordingly.
Light Spread: Ensure even light distribution to cover all plants effectively, possibly using reflectors or multiple light sources.
Growing Seedlings With Artificial Lights
Growing seedlings with artificial lights is an excellent way to ensure they receive the consistent light they need, especially in regions with less natural sunlight. Seedlings, the young and tender plants in their initial growth stages, are particularly sensitive to light quality, intensity, and duration. Artificial lights, including grow lights and high-powered house bulbs, can provide the ideal conditions for robust development.
Artificial Lights: Using artificial lights for seedlings ensures they get the right amount of light for optimal growth. Seedlings typically need about 14–16 hours of light per day. LED grow lights are highly recommended due to their efficiency and ability to emit the full spectrum of light that closely mimics natural sunlight. This spectrum is crucial as it includes both blue light for vegetative growth and red light for flowering stages. Additionally, LED lights produce minimal heat, reducing the risk of damaging young plants.
Grow Lights: Specialized grow lights are designed to provide the precise wavelengths of light that plants need. For seedlings, full-spectrum grow lights or those in the 5000K-6500K range are ideal, as they promote strong stem and leaf development. Fluorescent grow lights, such as T5 high-output tubes, are also a popular choice due to their balanced light output and energy efficiency. These lights should be placed close to the seedlings (within a few inches) to ensure adequate light intensity, but far enough to prevent heat stress.
High-Powered House Bulbs: While not specifically designed for plants, high-powered LED house bulbs with a daylight spectrum 5000K-6500K can also be effective for growing seedlings. These bulbs provide sufficient brightness and a suitable spectrum for early plant growth. However, it's important to monitor the distance between the bulbs and the seedlings to avoid excessive heat and ensure even light distribution. Using reflectors or positioning the bulbs strategically can help maximize the light exposure for your seedlings.
In conclusion, whether you use specialized grow lights or high-powered house bulbs, output matters more than the type of bulb. In our experience, no matter what bulb you use, the only thing that really makes any real world difference to seeds is the lumen output, which relates to the wattage of the light bulb. Higher wattage units usually output more lumens, which gives plants more available light for growth. When choosing a grow light for seedlings, be careful to check the correct distances, as they're more susceptible to scorching or burning under high intensity lighting. When growing seeds, be extra cautious about heat outputs, testing with your hand regularly as they grow.
Do Plants Grow Faster With 24 Hours Of Light?
It can be tempting when using grow lights to leave them on all night to give your plants more light, and to achieve faster growth. However, there are a few important factors to consider when using continuous lighting. The quick answer to this question is yes, 24-hour lighting does increase growth, but the catch is that the plants may suffer damage to their food production systems which could slow down growth over time. If you'd like to delve into the science behind continuous lighting, stay tuned.
There are several sources online promoting the use of 24 hour lighting when growing herbs or crops indoors, however, dark periods affect different plant species in different ways. There haven't yet been any studies on how continuous lighting impacts different houseplant species, so it's essential to monitor plants closely if you want to try this lighting technique. Let's have a look at the scientific aspects of how continuous light affects plant growth:
Photosynthesis & Light Intensity During 24-hour Light Cycles
Plants use light to perform photosynthesis, a process where they convert carbon dioxide and water into glucose and oxygen. This process primarily occurs in chloroplasts, specialized organelles within plant cells. Chloroplasts contain chlorophyll, the green pigment that captures light energy. By absorbing sunlight through chlorophyll, the chloroplasts convert this energy into carbohydrates, providing the plant with the necessary food source for growth.
During photosynthesis, plants also convert sunlight into oxygen, which is a sustainable way to improve indoor air quality. Although some plants may grow faster with continuous lighting, they don't keep photosynthesising all day and night during a continuous cycle. Photosynthesis typically follows a diurnal rhythm, meaning it occurs mainly during the daylight hours when light is available, and significantly slows down or stops during the night. This is because the light-dependent reactions of photosynthesis require light to produce energy carriers (ATP and NADPH), which are then used in the light-independent reactions (Calvin cycle) to synthesize glucose.
Consequently, 24-hour lighting doesn't provide continuous benefits for air quality since photosynthetic activity naturally declines during the plant's 'night' period, even if the lights remain on. This is because the rate of photosynthesis increases with light intensity up to a certain point before you reach diminishing returns. Continuous lighting can lead to photoinhibition, which occurs when the photosynthetic machinery within the plant gets damaged due to excessive light, reducing photosynthetic efficiency. This can cause stunted growth and prevent the plant from converting light to energy effectively. Therefore, for optimal growth, it's recommended to provide a balance of 16–18 hours of light and 6–8 hours of darkness. This balance supports both photosynthesis and essential dark-phase processes like respiration and metabolic regulation. If you use continuous lighting with your houseplants, monitor them closely for warning signs such as leaf burn, yellowing, or wilting to avoid photoinhibition. Generally, exposure to high light intensity for extended periods can cause stunted growth and prevent the plant from converting light to energy effectively. For optimal plant growth, it's recommended to provide a balance of light and darkness, typically 16–18 hours of light and 6–8 hours of darkness. This balance allows for both photosynthesis and essential dark-phase processes like respiration and metabolic regulation. Continuous light may accumilate damage over time, potentially leading to plant stress and photoinhibition. If you try continuous lighting with your houseplants, monitor them closely for warning signs such as leaf burn, yellowing, or wilting. We will explore the signs of damage later on in this guide.
Photoinhibition is a reduction in the photosynthetic capacity of a plant due to excessive lighting conditions damaging cells. It occurs when the light intensity exceeds the plant's ability to use the available the light for photosynthesis, leading to damage in the photosynthetic machinery, primarily affecting the photosystem II (PSII). Understanding what photoinhibition is helps in optimizing lighting conditions for houseplant growth to help prevent damage, and to ensure efficient photosynthesis to support the plant's vital functions.
The duration before photoinhibition occurs can vary depending on several factors such as light intensity, plant species, and acclimation to light conditions. Generally, exposure to high light intensity for extended periods can lead to photoinhibition. For example, the Oxford photoinhibition study has shown that Arabidopsis seedlings grown under low light can experience significant photoinhibition when initially exposed to high light for 30 minutes, three times a day. However, these plants can recover and even adapt to the conditions over time. Notably, while initial exposure to high light causes severe photoinhibition, the study has shown that Arabidopsis seedlings can acclimatize within two weeks of continuous light exposure. This acclimatization allows them to resume normal photosynthetic activity, achieving similar yields to control plants under regular light cycles.
In the Oxford study, plants grown under low lighting were observed to have severe photoinhibition at the beginning of the experiment, however, testing indicated that the plants recovered from photoinhibition within a few hours once transferred back to low light conditions. Complete recovery was achieved overnight, and the plants went back to photosynthesising as normal. Testing indicated that over time, the plants became acclimatised to the new conditions, and recovered from photoinhibition.
The plants achieved full recovery from photoinhibition whilst being kept in 24-hour lighting after two weeks of the experiment. After this period of acclimatisation, similar photosynthesis yields were seen to the control plants under normal light cycles. Recovery was achieved by keeping the plants under continuous lighting and allowing them to acclimatise to the new environment over time.
Phytochrome and Photoperiod Regulation During Dark Periods
Plants have light sensing photoreceptors called phytochromes that detect light quality and quantity. Phytochromes are a group of photoreceptors in plants that help detect light quality (wavelength) and the amount of available light to the plant for photosynthesis. This light sensing ability allows plants to respond to changes, ensuring that growth and developmental processes occur at the most advantageous times. Photochromes play a critical role in regulating various vital plant processes, such as seed germination, flowering, and shade avoidance, by sensing red and far-red light.
The photoperiod (the duration of light and dark periods) is crucial for these vital plant processes. For instance, long-day plants require longer daylight periods to flower, while short-day plants flower when the daylight period is shorter. Another great example of this is seeds — some plant seeds require long periods of darkness to achieve germination, this is to mimic the natural day-night cycles in the wild at the time of year they would normally germinate. This light sensing feature allows seeds to stay dormant until the environmental conditions are just right for them to germinate and grow, avoiding total failure of germination due to environmental factors.
You may have heard of stratifying seeds, this is a process where the seeds are forced to germinate at the wrong time by providing exacting conditions to replicate those in the wild. This could be a period of low or high temperatures to mimic the seasons, a certain amount of light to mimic the seasons, or moisture to mimic rain after a long dry spell. When you put seeds in the dark to encourage germination by mimicking winter, you are using photoperiod regulation to your advantage as a gardener. Without this ability to sense light, seeds would have to rely solely on temperature or moisture for signs that it's the right time to germinate, which could cause a false positive germination. This would cause the plant to die due to the incorrect environmental conditions to support healthy seedling growth.
Continuous Light Studies
Studies have shown mixed results regarding continuous light. For example, research on Eruca vesicaria (arugula/rocket salad leaves) showed that continuous light (24 hours) at low light intensity increased biomass and nutritional quality. However, the same study noted that the absence of a dark period could lead to stress responses in plants. Several studies have been done on growing crops and herbs, but few have been done on houseplants themselves. It's important to mention that these findings may not apply broadly to all plant species, as we don't yet understand the scientific impact of continuous lighting cycles on houseplants.
Shade Avoidance and Plant Architecture
Continuous light can also affect plant architecture. In a study on tomato plants, continuous light without far-red (FR) light led to shade avoidance responses, such as increased plant height and reduced fruit production. This is because the lack of far red light impacts the phytochrome system in the plants, leading to altered growth patterns. It's important to mention that these findings may not apply broadly to all plant species, as this study was only done on tomato plants.
Practical Recommendations
For optimal plant growth, it's generally recommended to provide a balance of light and darkness. Most plants benefit from a photoperiod of 16–18 hours of light and 6–8 hours of darkness. This allows for both photosynthesis and essential dark-phase processes like respiration and metabolic regulation. Accidentally leaving your grow light on for too long once in a while may not damage your plants too much, and is nothing to worry about. They're likely to recover within a few hours. If you leave artificial lighting on all day, every day, a build up of damage may occur in the photosynthesis machinery, which could cause the plant to suffer from photoinhibition. This could cause stunted growth, and prevent the plant from converting light to energy through photosynthesis. This could ultimately starve the plant to death if it is not remedied swiftly, or if the plant doesn't manage to acclimatise to the new lighting conditions. If you try continuous lighting with your houseplants, make sure to keep a close eye on them for signs of stress.
How To Avoid Damage in Continuous Lighting
Trying continuous lighting for your houseplants can be an interesting experiment, and very tempting when you read about the increased growth. However, due to a lack of studies on the effects on houseplant species, it's crucial to be aware of the potential risks, and how to manage issues if they occur. Here are some visible warning signs to watch for, and the steps to mitigate plant damage:
Light Stress Warning Signs
Leaf Burn: Leaves may develop brown, crispy edges or spots, indicating that they are receiving too much light.
Wilting: Even with adequate watering, plants may appear wilted or droopy due to stress from excessive light.
Yellowing Leaves: Leaves turning yellow, especially the leaves at the top can be a sign of severe light stress. Plants don't kill off top leaves as a part of ageing.
Slow Growth or Stunted Growth: Plants might grow slower or stop growing altogether if they are under light stress. Leaves may grow in smaller than usual.
Leaf Curling: Leaves may curl upwards or downwards as a response to excessive 24-hour light exposure.
Reduced Flowering: Flowering plants might produce fewer blooms, smaller blooms, or none at all.
Practical Tips for Managing Continuous Lighting
Use Timers to Control Light Periods: Automated timers can help ensure that your plants receive the right balance of light and darkness without the need for manual intervention. Set a timer to provide 16–18 hours of light and 6–8 hours of darkness. This helps maintain a consistent photoperiod, reducing the risk of photoinhibition and other light-related stress.
Monitor Plant Health Regularly: Keeping a close eye on your plants allows you to detect early signs of stress and take corrective action promptly. Check your plants daily for any signs of leaf burn, yellowing, wilting, or other stress indicators. Keep a journal to note any changes and responses to your lighting setup.
Adjust Light Intensity and Distance: Ensuring that your plants receive the appropriate light intensity can prevent overexposure and damage. If using adjustable grow lights, increase the distance between the light source and the plants, or use a dimmable feature to lower the intensity.
Implement Light Breaks: Introducing periods of darkness can help mimic natural conditions and give plants time to rest. If you notice signs of stress, turn off the grow lights for a few hours each day. This can help alleviate some of the stress caused by continuous lighting.
Use Light Reflectors for Even Distribution: Reflectors can help distribute light more evenly, avoiding hotspots that can cause leaf burn. Position reflectors around your grow area to ensure that light reaches all parts of your plants evenly. If your hand feels too hot near the plant, it’s a sign the light might be too intense.
Ensure Adequate Watering: Overexposure to light can increase water loss through transpiration, making it important to keep your plants well-hydrated. Water your plants regularly but avoid overwatering. Adjust the frequency based on your plant’s needs and the light conditions.
Gradual Light Adjustment: Gradually increasing light duration helps plants acclimate to new lighting conditions without shock. When transitioning to continuous lighting, increase the light duration slowly over several days rather than making abrupt changes.
Supplement with Shade: Use shade cloths or net curtains to reduce direct light exposure if you notice signs of photoinhibition.
Use Soil Moisture Sensors: These sensors can help you track soil moisture levels, ensuring your plants are neither overwatered nor underwatered. Install soil moisture sensors and check the readings regularly to maintain optimal moisture levels. There are portable moisture meters which you can carry around with you, fixed watering spikes which live in the plant pot for a quick glance moisture reading, or digital moisture meters, which gives you an instant, accurate reading.
Utilize Plant Health Apps: Apps designed to monitor plant health can provide valuable insights and reminders for care routines. Use an app to track your plant’s growth, watering schedule, and light exposure, and receive alerts for any issues detected.
Conclusion
While continuous light can be tempting to achieve faster foliage and root growth, it's essential to consider the specific needs of each plant species and the potential for photoinhibition and stress responses. 24 hour lighting can enhance growth under certain conditions, however, due to a lack of studies on houseplants, there is little information available on which species would tolerate continuous lighting in the long term. A more balanced approach with appropriate light and dark periods is usually the best strategy for healthy plant growth.
The Benefits Of LED Grow Lights vs Other Grow Lights
LED lights are an excellent choice for indoor plant growth due to their efficiency, longevity, and ability to provide the optimal light spectrum for plants. If budget and position within your home is no concern, then they are the best option for indoor plant growth. Here are some key benefits of choosing LED grow lights over other types:
Benefits of LED Grow Lights
Energy Efficiency: LED lights consume less power compared to traditional grow lights like HID (High-Intensity Discharge) and fluorescent lights.
Life Span: LEDs have a longer lifespan, often lasting several years, reducing the need for frequent replacements
Low Heat Output: LEDs produce minimal heat, reducing the risk of heat stress and allowing lights to be placed closer to plants.
Customizable Spectrum: LED lights can be tailored to provide specific wavelengths (colours) of light that plants need for different growth stages (e.g., blue for vegetative growth, red for flowering)
Types of LED Grow Lights
Full Spectrum LED Grow Lights: These lights provide a wide range of wavelengths, mimicking natural sunlight and supporting all stages of plant growth.
Red and Blue LED Grow Lights: These lights focus on the blue and red wavelengths, which are most effective for photosynthesis and flowering.
UV LED Grow Lights: These lights emit ultraviolet light, which can enhance the production of protective compounds in plants, improving resistance to pests and diseases.
IR LED Grow Lights: These lights emit infrared light, which can influence flowering and seed germination.
Choosing the Right LED Grow Light
Light Spectrum: Ensure the light provides the appropriate spectrum for your plants' growth stage (blue for vegetative growth, red for flowering).
Intensity and Coverage: Choose a light with the right intensity and coverage area for your indoor setup.
Energy Consumption: Consider the power consumption and ensure it fits within your budget and electrical capacity.
Adjustability: Look for lights with adjustable settings to fine-tune the light output as your plants grow.
Using full spectrum lighting is highly beneficial because the light colour mimics natural sunlight. This provides a balanced range of wavelengths that plants need at different stages of their growth cycle necessary for photosynthesis, ensuring that plants get the energy they need to grow and thrive. Full spectrum lights also support the production of chlorophyll, which is crucial for photosynthesis and healthy, vibrant foliage. When plants don't get enough light, they can lose their patterns and colours as they try to produce more chlorophyll (the green parts) in their leaves.
Providing the right type of lighting for your houseplants ensures that they keep the patterns that you fell in love with when you purchased them. Full spectrum LED lights can help prevent uneven growth by providing consistent light quality, which can reduce the risk of plants becoming leggy or weak Some full spectrum lights also include UV (ultraviolet) wavelengths. UV light can benefit plants by stimulating the production of protective compounds, enhancing their resistance to pests and diseases. Traditionally, this has only been used in the production of indoor herbs, but more research has been done recently which shows the benefit to all types of houseplants. Growing plants under a UV spectrum can lead to stronger, healthier foliage with better overall resilience. However, it's important to use UV light in moderation, as excessive exposure can harm plant tissues and cause bleaching of the leaves. Ouch!
When choosing grow lights for indoor plants, LED setups are the most efficient and provide the most plant growth indoors. Although supplementary lighting can help, to achieve true plant growth rates, it's essential to match the plant's individual species requirements. This may mean adding several high-powered house bulbs, or one big grow light, depending on your budget, setup, space, and plant's individual needs. When selecting a LED light, we always recommend going for one with the highest wattage that you can get, as this is the direct correlation to light output, which helps plants to grow. We've had great success in our shop using numerous high-powered house bulbs, but if you can purchase one big unit, it can be easier to maintain over the long term.
Supplementary Lighting Summary
Artificial lighting is a great way to supplement light levels in your home for houseplants. We've explored what kelvin is best for plants, what light colour does to plant growth, and the benefits of adding artificial lighting. We covered LEDs, fluorescent lights, high output house bulbs, and grow light alternatives. While artificial lighting can significantly enhance the growth and health of indoor plants, it's essential to strike a balance between light and dark periods to avoid stress and photoinhibition. Adjusting grow light distances, or using tools like timers, light reflectors, and plant health apps can help manage light exposure effectively. By understanding the specific needs of each plant species and implementing practical strategies, you can create an optimal environment for your indoor plants to thrive.
Edited & Fact Checked By: The Houseplant Shop
Article Published: 11th December 2024
About The Houseplant Shop:
Independent Houseplant Nursery
Horticultural Specialists
Managing Over 250 Houseplant Species Onsite
Over 15 Years Of Experience With Horticulture
As head of horticulture, Sarah manages the care and propagation of over 250 plant species at a commercial houseplant nursery. With over 15 years of experience in horticulture, specializing in houseplants, Sarah has extensive expertise in plant biology, soil science, and integrated pest management. She continually reviews and integrates the latest research into her plant care guides. Dedicated to educating others, Sarah has spent years diagnosing houseplant care issues and sharing her real-world experience. Her commitment to scientific accuracy and helping people diagnose plant health issues has established her as a trusted authority and expert in the field.
The Houseplant Shop is a dedicated houseplant nursery, growing all of their own stock from their botanical library of over 250 houseplant species. The nursery staff are horticultural experts who have dedicated their lives to cultivating and nurturing over 250 different species of houseplants, focusing on Aroids, tropical plants, and NOID collectables. All their plants are grown in house in Britain to be more environmentally friendly. The nursery is proud to have been featured by the Royal Horticultural Society (RHS) as a 100% peat free nursery.
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How We Reviewed This Article:
Our horticultural experts continually monitor the houseplant space, and we update our articles when new information becomes available. We are committed to providing current and reliable information. If you have some information that you think would be helpful in this article, we'd love to hear from you. Our team works hard to revise articles for factual accuracy, and we regularly update our pages with new information, techniques, tips, images, trade secrets, and real world experience from the team here at the houseplant nursery. You can find a list of the article updates below.
Written By: Sarah Brooks, Head of Horticulture
Article Received: 8th December 2024
Copyright: The Houseplant Shop (https://thehouseplant.shop)
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List of Article Updates:
20th December 2024: Minor UI updates
Author Bio:
Author: Sarah Brooks,
Head of Horticulture at The Houseplant Shop