In our last post, we talked about the significance of lighting for pant growth in terms of light intensity, photoperiodism and light quality. In plant growth, light intensity is expressed as photosynthetic photon flux density (PPFD). It depends on both the optical design of the fixture and the number of photons emitted by the light source.

So what are the advantages of LEDs over conventional lights in providing sufficient light intensity for plant growth?

Let’s suppose there is a plant growth environment, where the plant is growing in the nutrient solution right under the lighting fixture on the ceiling. Only the light downward can reach the plant surface and be absorbed, while the upward and sideward light cannot. Figure 1 describes the light paths of traditional light sources and LEDs without optical design. Let’s say these four lights emit the same amount of photons, and the light from a traditional fixture, due to its broad viewing angle, is largely compromised and wasted if without any reflection accessories. Moreover, the reflector itself has an absorption rate that causes light loss. If the fixture requires small viewing angle, the reflecting angle must be small too. So for a light bulb or a tube light, the light upward and sideward is reflected multiply between the reflector and the fixture, leading to huge light loss and low efficiency. While when it comes to the LEDs, it is different. The LED itself has a small viewing angle, making the utility rate much higher, even without any additional reflectors. Besides, the LED dissipates small amount of heat, so optics made of low-priced resin can be added directly onto the light source, instead of any additional reflectors. In this way, the original 120° viewing angle can be decreased to any angle smaller (which is normally 15° on the market).