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How does Light Spectrum affect Plant Growth?

Before we begin, first we need to know how much light spectrum we have in the universe. Like showed in figure below, what human eyes can see (visible spectrum) is just part of the whole light bands, and that doesn’t mean plants don’t use lights we can’t see, such as UV and IR.

light spectrum

Based on our knowledge of plants in the nature, most people must think plants need the entire light spectrum from the sun. And correspondingly, the best LED grow lights should be the full spectrum ones too. Really? Let’s see about it.

wavelength of light

So the answer is, NO. The most used light spectrum is blue and red, which has been proved by many studies. This is mainly because the early leafy plants first appeared at low levels in the ocean and above them are the bacteria which used yellow, green and orange spectrums for photosynthesis. So the plants were left only with other spectrums composed mainly of red and blue. So even if we give the plants full spectrum, the yellow, green and orange light will be mostly reflected away off the surface of the leaves. That’s also the reason why the leaves are green.

How do different spectrums affect?

As we can see in the above picture, each plant has so many pigments to absorb different spectrums for photosynthesizing. To simply it, there is only one parameter we need to focus on, the oxygen output, which is an important sign of photosynthetic activity. In this way, we know exact relationship between spectrums and plants growth.

ultraviolet light

Ultraviolet light (10nm-400nm)

UV light includes UVA(320~400nm),UVB(275~320nm), UVC(200~275nm) and UVD(100~200nm). And studies showed slight amounts of UV light, especially UVB, will have good effect on plants taste, color and fragrance.

Blue light (400nm-480nm)

Blue light has a positive help on production of leaf, resin and fragrance in plants, which is very important for flowers and other plants in their pre-flower growth stage.

Green light (480nm-550nm)

As mentioned above, green light is the least light used in photosynthesis. But to some strain, it is a must for normal growth since green light is coordinator to some degree when working with blue, red and far-red light. And chlorophyll doesn’t absorb green, which is most absorbed by Carotenoids deeper in the leaf structure, so it is believed green light has a better penetration into the canopy.

Red light (630nm-680nm)

Red wavelength, especially 660nm, is supposed to have significant effects on plants stem growth, flower production and yield in flowering and ripen stage. This is very important to increase the unit value of flower and other cash crop.

Far red (730nm)

Far red, one segment of infra-red, is not so needed as red light, but still necessary for plants which need low values of the phytochrome photoequilibrium to flower. And it can also help the plants to stretch, so don’t use it to compact desired plants.

What is the optimum Spectrum mix?

The answer is there is NO perfect spectrum mix for all plants or a single plant in different growth stage, in which they require variable spectrum and intensity of light wavelength. So what you really need is an LED grow light with intensity and spectrum programmable, or you will have to move the plants from A to B at different growth stages, or you will waste a lot of energy without the most yields.

Choose the easiest control

Since we need to program the LED grow lights, do you prefer to control it by controller installed on the wall or just on your PC and cell phone? If you choose the latter, then ZSP has what you need.