It would be remarkably convenient if a single number could be used to compare different types of grow lights. Many companies try to express their lights' performance as a single, impressive PAR, lumen, YPF or other intensity measurement, but this certainly does not tell the entire story.

Any of these measurements can be manipulated to make a grow light look impressive on paper, but they don't indicate how well the light will grow plants. A $5 0.005-watt laser pointer has PAR and YPF readings comparable to some of the most impressive grow lights on the market, but it won't grow a plant. Just as a single number cannot be used to fully compare cars, a light's plant-growing performance cannot be distilled to a single number.

By far the best way to compare lights is to perform a side-by-side test yourself; only in this way can you see through marketing hype to the actual relative performance of the light. At Black Dog LED we encourage everyone to try their own side-by-side tests with our lights to see for themselves just how well they grow plants, but we appreciate that this is not always possible.

Three-way side-by-side grow test: Black Dog LED, CMH and T5

When comparing different grow lights, it’s important to consider:

    • The spectrum of the light:
      • Ultraviolet (UV) light is important to stimulate production of secondary metabolites such as pigmentation, flavonoids, THC and CBD.
      • Far red / near-infrared light (NIR) is important for hormonal signaling in plants and maximizing photosynthetic efficiency due to the Emerson Effect.
      • The total spectrum is important. Many LED grow lights include only 2-6 component colors; some attempt to make up for this by using white LEDs to "fill in" the gaps in their spectrum, although this is not the most efficient way to do it.
      • 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.
      • Using different "vegetative" and "flowering" spectrums actually stresses plants and decreases quality. A spectrum which works for both vegetative and flowering also allows for greater flexibility with the lights.
    • The intensity of the light- not just at a single point, but over the entire growing footprint at the recommended hanging height.
    • The efficiency of the light, relative to its ability to grow plants. The most-efficient lights possible can't be used to grow plants, so efficiency alone is not enough- intensity is required.
    • 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 grow lights 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.