With all the talk about grow lights, whether for commercial greenhouse lighting or a home project in a tent or in a garage, it can get overwhelming hearing about lumens, lux, PAR, footcandles, and now PPE, PPF and BPF or YPF. All of those terms measure light to know the output of light sources and the spectral range. But what about the actual spectrum output of a light source? Whether a bulb of some type, like HPS or CFL, plasma or LED lighting, what difference does the spectrum it emits make for your plants?
You’ll search and see or hear terms like “daylight spectrum light”, “full spectrum led grow light”, “full spectrum plant lights”, or more specific terms like “full spectrum LED light for plants”. What do they all mean and why should any of this matter to you? A couple questions come to mind: is whatever light source you’re researching made for plants? And what is the actual spectrum emitted by the fixture?
The old adage “intensity equals density” does matter and knowing what your chosen crop lighting requirements are for intensity level and hours per day will most definitely help you on your quest to crush it in your garden. But what benefit does the actual spectrum emitted bring to you and your plants? Whether you have a fancy light meter that measures all of the industry buzz phrase acronyms or just a simple lux meter which can measure intensity fairly quickly and cost effectively, you still need to know what the spectrum is of your grow light and whether that it is actually a full spectrum grow light or just called that. Just called that? What the hell does that mean? Well… in this new wild west-like frontier of grow lighting there are players who make claims and have all the buzz phrases, yet they may not be necessarily forthcoming with truth in their advertising. They all get caught eventually and are called out for it, but many people still get taken for an unhappy ride, buying into marketing hype only to be mad afterwards.
Recognizing and verifying certifications such as DLC or UL800 by looking up what is posted in advertising materials will help you tremendously. Luckily for most of us, we have eyes that can see, and these absolutely wonderful eyes of ours can tell quite well what intensity is and even what the quality of the visible spectrum is of any given light source. When you see a light that is bright and “bluish” once you’ve grown a plant, you’ll know that color family best suits vegetative growth, and that “orangey” intense light is better for flowering plants. Our eyes are not deceiving us there at all, and we can see the bulk of the range that plants actually use…but not all that they need for optimum growth. That’s where a spectrum chart comes in handy. With a spectrum graph or chart you can see if a light source is truly full spectrum or not. So what does a big grow light need to show in order to be legitimately considered full spectrum? The answer is like a good sauce—it needs a little bit of everything to round out the flavors, or in this case, colors or light to fulfill our chosen crops dietary requirements.
That means that roughly from 350nm to 850nm, which is now considered a more accurate horticultural range of what plants actually use, there should be nothing missing. The “doses” of each bandwidth will undoubtedly be argued but all of it must be there to be allowed to be called full spectrum.
An HPS bulb does work (but uses too much power and creates too much heat but that is a whole separate discussion) but upon seeing its spectrum chart you’ll see plenty of bandwidths missing or not represented which clearly shows that they are not full spectrum grow lights.
Granted we all know the sun is the OG of light sources and generally seen as the best for plants, but we don’t stare at it as our eyes can’t handle that intensity. That goes for good grow lights too— never stare at them just like you wouldn’t stare at the sun. With that logical caveat out of the way, we can talk about full spectrum lighting and the effects it has on crop yields and quality.
If you’re growing flowering plants, whether equatorial or from mountain ranges further from the equator, they all need light to grow. All flowering plants have adapted to a specific climate and region for the most part and the naturally occurring spectral range there. Sure, we water plants and give them nutrients in some form or another, but did you know that plants actually eat light? Water and nutrients do help, but they actually eat light to promote photosynthesis, which then induces the plants to “drink” and “sweat”.
Combine true full spectrum horticultural lighting with intensity and your crops will pay you back with better quality and bigger yields. Your choice of full spectrum horticultural light does matter.