The effect of colored light on plant growth is an interesting area of study for botanists, gardeners and indoor plant enthusiasts. Some preliminary research has suggested that red colored light may promote increased growth and flowering in certain plant species. This article will examine the evidence and theories behind whether red light specifically boosts plant growth.
How Plants Use Light
Plants require light for photosynthesis, the process by which they convert sunlight into chemical energy. Photosynthesis primarily relies on blue and red wavelengths from the visible light spectrum.
Chlorophyll, the green pigment in plant leaves and stems, absorbs red and blue light most efficiently. These two colors of light drive photosynthesis and allow the plant to carry out critical functions like respiration and transpiration.
However, plants also use other wavelengths of light. Green light penetrates leaves further than red or blue and helps under-leaf photosynthesis. Red and far-red light help regulate dormancy and germination. Overall, a diversity of light wavelengths supports optimal plant health.
Research on Red Light Effects
So does red light, specifically, boost plant growth? Initial research indicates some benefits for supplementing white or full-spectrum light with red wavelengths.
| Study | Plant Species | Red Light Effects |
|---|---|---|
| University of Maryland (2014) | Lettuce | Increased biomass and leaf count |
| Michigan State University (2012) | Tomatoes | Increased fruiting and taste |
| UC Davis (2021) | Strawberries | Earlier flowering and fruiting |
These studies saw growth, flowering and yield gains in multiple plants grown under supplemental red LEDs or filters. The gains were most significant when combined with blue light, which enables full photosynthesis.
There are a few hypothesized reasons why red light may spur plant growth:
– Increased light absorption for photosynthesis, as red is a peak absorption wavelength
– Adjusted shoot/root ratios, directing growth above ground
– Stimulation of phytochrome receptors, which regulate growth and flowering
– Changes to the quantity or quality of plant compounds produced
More research is still needed to fully understand the morphological and biochemical effects of red light on various plant species.
Considerations for Using Red Light
While red light shows promise for improving plant growth, there are some important factors to consider:
– **Intensity** – Red light must be intense enough to penetrate the plant canopy and reach lower leaves. High intensity red LEDs often give the best results.
– **Wavelength** – Researchers use pure, 660 nm red light. Colored glass or plastic filters also work but may not isolate the red spectrum.
– **Duration** – The length of daily red light exposure can impact results. Some plants respond best to red light early or late in the photoperiod.
– **Stage of Growth** – Young plants may be more responsive to red light than older, slower-growing plants. The effect can also vary by season or flowering stage.
– **Type of Plant** – Flowering, fruiting and leafy plants tend to show more growth under red light compared to vines, succulents or dormant plants. But responses can vary widely between plant genera and species.
With these considerations in mind, gardeners can experiment with red light to determine if it benefits particular plants. Home growers can use red LEDs or filters, while commercial operations may invest in customized red + blue greenhouse lighting rigs. Proper intensity, exposure times and monitoring will help optimize results.
Potential Drawbacks of Red Light
While red light has advantages, relying solely on red wavelengths can also pose problems:
– **Stunted growth** – Extended red light without blue can reduce plant size and biomass by limiting photosynthesis.
– **Deformed growth** – Abnormal stem elongation and mutant leaf shapes may occur under pure red light, especially at high intensities.
– **Poor color** – Red light causes weaker chlorophyll production, resulting in pale, washed-out leaf color in green plants.
– **Tip burn** – Excess red light encourages leaf tip necrosis, especially in lettuce and greens.
– **Flower/fruit issues** – Too much red light can cause flowering problems, smaller fruits and lower quality yields in some plants.
Optimizing Red Light for Plant Growth
Research indicates red light works best as a supplement to full-spectrum white or blue light, rather than the sole light source. Here are tips for optimizing red light balance:
– Use white or blue light as the primary source for 12-16 hours daily. This enables robust photosynthesis.
– Add red light for 2-4 hours mid-day or at sunrise/sunset. Limit red light to 25-50% of total daily exposure.
– For flowering/fruiting plants, increase red light ratio to 30-60% during bloom stages for maximum yield.
– Use 660 nm pure red LEDs or filters. Avoid colored grow lights that skew more pink/purple.
– Position red light above mature leaves which require more far-red light absorption.
– Adjust intensity to 30-100 μmol/m2/s, raised as canopy thickens. Monitor for tip burn.
– Watch plants closely and adjust red light hours/intensity based on appearance and growth.
With the proper balance, red light can boost plant health, size, flowering and fruit production without abnormalities.
Conclusion
Research suggests red LED lighting can act as a beneficial supplement to encourage faster growth, earlier flowering and higher yields in some plant species. However, excessive red light can also cause deformities and problems if not balanced with a full-spectrum source. Gardeners have the most success using red light strategically during particular growth phases and at moderate intensities below 50% of total exposure. When optimized properly, red light is a useful tool to promote vigorous plant growth. Continued research and controlled growing trials will help refine best practices for using red light on various plant types.
