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How to Compare Different Grow Lights

It would be remarkably convenient if a single number could be used to compare different grow lights,lumen or other intensity measurement can not decide the light is good for growing or not.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. 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.

When comparing different grow lights,side by side growing will help you or the following information is important to consider:

• The spectrum of the light:

1.Ultraviolet (UV) light is important to stimulate production of secondary metabolites such as pigmentation, flavonoids, THC and CBD.

2.Far red / near-infrared light (NIR) is important for hormonal signaling in plants and maximizing photosynthetic efficiency due to the Emerson Effect.

3.The total spectrum is important. Many LED grow lights include only 2-6 bands colors; some attempt to make up for this by using white LED to "fill in" the gaps in their spectrum, although this is not the most efficient way to do it.

4.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.

5.Using different “vegetative“and “flowering”spectrum actually stresses plants and decrease 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.


• 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:

1.Rectangular light configurations which supposedly have a square lighting footprint.

2.Lights which violate the laws of physics by putting off less heat than the power they consume:1 watt of power equals 3.412 BTU per hour run.

3.Creating more light using lenses.

4.Coverage areas that defy belief.

• For LEDs in particular, the design of the light is critical as well:

1. 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.

2. Primary lenes 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.

3. 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.

4. 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.

Lumens: Why They're Not That Important

Luminous flux is a measure of the amount of light that is visible to the human eye, and lumens are the unit used to describe this measurement. So, why don't lumens matter when it comes to growing plants? Basically, lumens will show you how well a human eye will be able to see under a given light source... but plants don't have human eyes.

Plants have a variety of pigments that use the energy in light to convert carbon dioxide and water into sugars (this process is known as photosynthesis). Different pigments use different wavelengths of light to accomplish this task: Chlorophyll a absorbs red and dark blue light; Chlorophyll b absorbs orange and light-blue light; Carotenoids absorb blue, purple, and ultraviolet (UV) light; and green/yellow light is essential for phytochrome response. While there is some overlap between the wavelengths of light useful to the human eye and those useful to plants for photosynthesis, different wavelengths are more important for each function. For example, the human eye is most sensitive to yellow light, so the measure of lumens is weighted with respect to that particular range of wavelengths, while photosynthetic plants make the most use of red and blue light. Another important consideration is that many plants utilize non-visible wavelengths of light. For example, UV light stimulates the production of defensive chemical compounds in many plants and specifically trichome and terpenoid production in cannabis. Lumens don't provide any information about the UV or far red (FR / NIR) or infrared (IR) content of a light source.

Lumens will give you some information about the power of a light source, but it is more important to pay attention to the combination of Photosynthetically Active Radiation (PAR) and Yield Photon Flux (YPF). Measured in micromoles per second and per square meter (µmol s-1m-2), PAR shows how many photons in the 400 to 700 nanometer (nm) range of wavelengths are being emitted by a light source. The number of photons emitted is useful because photosynthesis takes place when a photon of light is absorbed by a reaction center located inside a photosynthetically active pigment. PAR still isn't a perfect measure of how a grow light will perform. YPF is a weighted measure of photon flux between 350 and 800 nm, meaning that it takes into account which exact wavelengths of light are most useful to plants and assigns those wavelengths a greater value of usefulness. YPF includes wavelengths outside of the visible range of light, which can cause the production of useful chemical compounds in some plants. A combination of wavelengths, including outside the visible range, is beneficial when growing plants under artificial light.