Continuing the discussion from PPFD Grow Light Comparision:
TL;DR (too long, didn’t read): Comparisons of grow lights are necessary and important for consumers but light is a tricky topic. Spreading misinformation willing or unwittingly has the same negative effects. We should do our best to keep basic principles and physics in mind when doing these studies.
Discussing light and lighting fixtures is not a trivial topic. I started my degree in optical engineering 4 years ago and still find myself consulting text books and my notes regarding light. That’s why I think grow light comparison videos are a great way to untangle difficult vocabulary and concepts around lighting for growers and consumers alike. However, after seeing a few of these videos, there tends to be some amount of myth and mystery weaved into each one.
I want to first thank KIND LED for taking the time to put together this video and then share it to the community. I do believe that addressing lighting concerns for controlled environment agriculture is one of the major paths toward a sustainable alternative to traditional ag.
To start, it is indeed important to distinguish between photometry and raidometry. However, the definition for radiometry provided is lacking quite a bit and these two topics end up getting crossed later in the video. Radiometry is the measure of electromagnetic radiation from a source or on a target in space. With radiometry we are able to understand the light distribution from a source or on a target in both angular and spatial extend as well as the transport of light from source to target.
@3:00 there is a quote “Photosynthetic receptors in plants are activated by the photon itself, not the energy contained within that photon.” A photon is a quantized unit of electromagnetic (EM) radiation and has no mass, it is pure energy. A photoreceptor takes incident EM energy and converts it into an internal signal. That signal drives a number of processes, photosynthesis being the most well known.
@9:08 referencing white LEDs and their green/yellow content, you say “Many of these photons will be reflected by the plant.” This is a very dangerous statement in a video such as this. There is a ton of stuff packed into that statement. When light is incident on a surface it can transmit, absorb or reflect. Green light is highly transmissive in leaves! This is how shaded leaves actually survive while trying to grow into better quality light. Saying that “many” of these photons reflect from the surface is very misleading. The amount of light reflected is dependent on the index of refraction of the leaves. Furthermore, there are cartenoids that have absorption peaks in this green and yellow range. With so many variables at play, generic statements like this are dangerous because it’s easy to take these statements at face value.
It’s great to openly discuss various topics and analyze grow light systems but caution needs to be taken with what information is spread. Physics gives us the tools to help us understand how light quality and quantity affect the plants we care so much about, so I just think we should care equally about how we interpret and use these tools.