Which Colors do Plants Use?
Plants use light mostly for photosynthesis and this is done with specific chemicals in the leaves. Examples of the more important chemicals include Chlorophyll A and B. In the absorbance spectrum (measures how much light is absorbed) you can clearly see the peaks in the blue and red regions which means that these colors are used for photosynthesis.Almost no light is absorbed in the green range.This has led to the incorrect conclusion that plants only need blue and red light.
The Myth of Blue and Red
Light wavelengths absorbed by plants for photosynthesis LED
Light wavelengths absorbed by plants for photosynthesis
The idea that plants grow well with only blue and red light is in fact a myth. The above color spectrum is for purified chlorophyll in a test tube and it does not show you what happens in a plant leaf. Photosynthesis is more complex and involves other chemicals like carotene and xanthophyll. A color spectrum of the light absorbed by the whole leaf shows that plants actually use a wider range of wavelengths, including green.
It is true that blue and red are important and represent most of the light used by plants, but other colors, including green and yellow are also used for photosynthesis.
How the Light Spectrum Affects Plants
- Red Light (630 -660 nm) is essential for the growth of stems, as well as the expansion of leaves. This wavelength also regulates flowering, dormancy periods, and seed germination.
- Blue Light (400 -520 nm) needs to be carefully mixed with light in other spectra since overexposure to light in this wavelength may stunt the growth of certain plant species. Light in the blue range also affects the chlorophyll content present in the plant as well as leaf thickness.
- Green Light (500 – 600 nm) penetrates through thick top canopies to support the leaves in the lower canopy.
- Far Red Light (720 – 740 nm) also passes through dense upper canopies to support the growth of leaves located lower on the plants. In addition, exposure to IR light reduces the time a plant needs to flower. Another benefit of far red light is that plants exposed to this wavelength tend to produce larger leaves than those not exposed to light in this spectrum.
What is Color LED Light Best for your Eyes?
The Best Spectrum for Growing Indoors
The spectrum you select tells your plants what to do when by guiding them through the seasons. If you’re growing indoors, you have to completely recreate the sun for your plants through variable spectrum LED grow lights.
Here’s what a typical growth cycle should look like:
Seedlings
If you’re starting from seeds, you want to give your seedlings 24-hour light, but at low intensity. Stick to about 15% red and 30% blue and white. When your seedlings get their first set of true leaves, you can double the intensity until they have more than two sets, at which point they’ve graduated to the vegetative stage.
Clones
If you’re starting with clones, your first goal is to encourage rooting. This takes some effort on your plants’ part, so keep the light intensity low. If you stick to about 25% red and 45% blue and white, your plants is more likely to focus energy on deepening roots rather than expanding upward.
Vegetative Stage
In the vegetative stage, your top priorities for your plants should be root growth and developing nice, tight internodes. For this, a healthy dose of blue light is your best bet. A higher concentration of blue keeps plants a little shorter. You don’t want your plants to shoot up too fast, develop longer internodes, and create a situation in the flowering stage where taller leaves form a canopy blocking light from the buds that grow lower on the plant. Keep your blue and white light levels blasting at 100% and maintain red at less than 60%.
Pre-Flower Stage
The pre-flower stage is when you should start prioritizing bud growth. Remember how plants take the red-light signal from the sun to start flowering? That’s the natural reaction you want to tap into now. An increase in red will inspire your plants to sprout buds. However, you do still want to be careful of bathing your plants in too much red. You should avoid flowering stretch at this stage, and the red light does tend to make plants reach skyward. At pre-flower, your wisest move is to kick the intensity of red light up just a little, to about 80%. Your blue light concentration can remain right where it was.
Flowering Stage
This is the red spectrum’s time to shine, so to speak. Up until now, you’ve been shielding your plants from a blast of red light to prevent stretching, but now your plant needs all the photons it can get. Turn your red light spectrum—that’s red and deep red—up to 100%. This maneuver helps you get those higher-than-ever yields.
The rest of the channels in your variable spectrum can stay at 100% as well. It’s all hands on deck in the flowering stage. Too much blue light will divert energy to the leaves and away from the buds. This will give fluffy buds with a lot of leaves. Very high power in red with a low level of blue is the key to maximizing yield and dense flowers.
Finishing Stage
This is where you manage your potency and chemical profile. As you recall, blue and white light are the heroes when it comes to producing trichomes. Prioritize blue and UVB at 100%, and turn red down to about 50%. This is how you get those sticky buds everyone is looking for.
If you’re new to variable spectrum LED lights, this may seem like a lot to manage. Fortunately, you can actually program and automate the entire growth cycle with technology like the Solar System Controller.
Of course, this is all strictly indoor lighting. If you’re growing in a greenhouse, the considerations are a little different.
Color Spectrum of LED Bulbs
It is important to distinguish between LED bulbs and LED lights. An LED light is the complete fixture and it can contain one or more LED bulbs; usually more than one. The LED bulb is the small individual component that makes light.
LED bulbs exist for specific wavelengths. This image shows the spectra of three bulbs; blue, yellow and red. Note that each bulb produces a fairly narrow spectra. The blue bulb for example is about 60 nm wide, and contains only blue light.
Since many people believe that plants need only blue and red light, many of the lower cost LED lights offer only blue and red LED bulbs. This seems like a perfect solution, especially since blue and red LED bulbs are more efficient and less expensive than other colors.
A lot of the LED grow light pictures on the internet show a ‘burple’ light – the industry name for the color made by using a combination of blue and red LED bulbs.
LED bulbs are now available in more than a dozen different colors.
While they are considerably more expensive than fluorescent bulbs, LEDs use half the electricity and last five times longer, more than paying for themselves in the long run. The average LED bulb from the hardware store is not designed for plant growth, however – you need special , a relatively new technology that is increasingly available from horticultural suppliers.
LED grow bulbs are capable of much greater light intensity than fluorescent bulbs and are available in full-spectrum form. An easy rule of thumb: Fluorescent bulbs are often used when growing just a handful of plants; LEDs are preferable for larger quantities since you can achieve higher light intensity per square foot. Another advantage of LEDs? They produce very little heat compared to other bulbs – an issue that can become problematic when you have a lot of lights in a small space.
Before the advent of LED grow lights, were the main option for large indoor plantings. They are extremely powerful, but are expensive to purchase, consume electricity inefficiently, require special light fixtures, and give off a lot of heat. All that said, they are very effective and are still widely used. If you want to grow large plants like tomatoes or lemon bushes, HIDs are good bet because the light penetrates farther into the foliage than with other bulbs.
There are two types of HID bulbs. High-pressure sodium (HPS) bulbs are best for flowering (low spectrum), while MH (metal halide) bulbs are required to support vegetative growth (high spectrum); the two types are often used in conjunction. Unfortunately, each type requires its own fixture.
One of the most important functions of UVB is that it improves the production of THC. The latter is a cannabinoid, which is believed to be a defense mechanism of the weed. When there is UVB grow light, it has greater UV exposure. The outcome is that it will defend itself against ultraviolet radiation, which is why it can produce a higher level of THC.
