No matter what companies may say, there’s no way to sum up a growlight’s performance in a single number. Many companies try to express their lights’ performance as just an impressive intensity measurement such as PPF or lumen, but this can’t tell you the whole story. Just like how you can’t compare cars using only a single number, growlights need more than just one impressive statistic to prove itself.
Any measurement can be omitted or manipulated to make a growlight look impressive on paper, but they can’t tell you how well a light can grow plants. Did you know that a 0.005W laser pointer has a YPF and PAR comparable to some of the strongest growlights on the market? This doesn’t mean a laser pointer will grow a plant.
When comparing different growlights, it’s important to consider:
The spectrum of the light:
Ultraviolet, or UV light is important to stimulate production of pigmentation, flavonoids, THC and CBD.
Far red, or near-infrared light is important for hormonal signaling in plants and maximizing photosynthetic efficiency.
The total spectrum is important. The component colors of the light must be present in the correct ratios. For example, too much far red / near-infrared light or too little blue light will cause plants to “stretch” and get leggy. However, using different “vegetative” and “flowering” spectrums actually stresses plants and decreases quality; the ideal light will be able to be used with both states. That also allows you more flexibility in lighting.
The intensity of the light over the entire grow area:
Taking a measurement from a single point is not an accurate way to judge a light’s intensity
The efficiency of the light, relative to its ability to grow plants:
Remember that the most efficient lights possible can’t be used to grow plants, so balance light efficiency and intensity.
Impossible claims the manufacturer / seller of the light makes:
If they are lying to you about one thing, what else are they lying to you about? For example:
Rectangular light configurations which supposedly have a square lighting footprint.
Lights which violate the laws of physics by putting off less heat than the power they consume. The conversion is fairly simple: 1 watt of power equals 3.412 BTU per hour run. So if the seller is claiming their 650W light puts off 500 BTU of heat, something is wrong.
Creating more light using lenses. Lenses don’t create light– if they could, why not just use lenses to grow plants?
Coverage areas that defy belief, for example a 120W LED panel that covers a 4’x4′ area for flowering.
The ease-of-use of the light:
If there are supplemental side-lights for changing the spectrum that are supposed to be turned on daily for a period of time, is it possible to do this with a timer? If you have to manually flip a switch, you have to remember to turn it on and off again every day.
If the manufacturer suggests getting voltage-regulators to “protect” their light from normal household conditions, why didn’t they just build that in to the light?
For LEDs in particular, the design of the light is critical as well:
Without effective heat dissipation, LEDs can burn out within days or months. Passive cooling (without fans) works for 10-20 watts of LEDs in household settings, but running high-power LEDs in close proximity (as needed for growing plants) requires fans to keep the LEDs from degrading.
Primary lenses harvest more light from the LED, making it more efficient. The beam angle of these primary lenses should spread the light over the entire footprint.
Secondary lenses focus the light to give it an impressive PAR, YPF or other intensity measurement, but only at a single point, destroying the light’s total growing footprint and losing about 10% of the light in the process.
Reflectors are counter-productive with LED lights; if a light has a reflector built-in, the beam angle of the primary lens wasn’t chosen properly, or the primary lens is missing entirely.
Even with all these things considered, it still isn’t easy to compare growlights based on product specifications. Searching the internet for legitimate, documented grows can be useful. It’s fairly easy to hang a light above some existing plants to take a picture and make it look like the light works, so single pictures should not be trusted. There are numerous grow journals which cover the first week or two of growing with a light and then mysteriously end; this often happens when the grower gets too busy to continue documenting everything, but if you can’t find a single start-to-finish documented grow with a light, there may be a reason for it.