Most Plant Grow Lights are Human Lights in Disguise

Every artificial grow light technology on the market was originally designed to provide light for people. Some lighting technologies such as fluorescent / induction, HPS, MH, CMH / LEC, plasma and white LEDs happen to include enough of the right colors of light to be able to grow plants; others such as LPS (Low Pressure Sodium) work OK for people but can't be used to grow plants at all. The truth is, plants and human eyes have almost opposite needs when it comes to colors of light. This is not a coincidence at all: our eyes evolved to help us see plants, so we're most sensitive to the yellow and green colors plants reflect the most and use the least.

The graph below shows this:

• The yellow-green line shows the relative color sensitivity of the human eye, showing how our eyes are most sensitive to yellow and green light. This is also the lumen weighting function which is used to measure lux / lumens for a light source.
• The green line shows the relative color sensitivity of plants, which is lowest in the yellow and green region of the spectrum.
• The orange line shows the spectrum of a High Pressure Sodium (it's even a "blue-enhanced agricultural" HPS) light; you can see how most of its light is in the range people are most sensitive to, and plants are least sensitive to.
• The purple line shows the Black Dog LED Phyto-Genesis Spectrum™, with most of its light being generated in the colors plants want most, but that people are least-sensitive to.

You can play around with graph to add other lights' spectrums and see how most so-called "grow lights" are more ideal for humans than for plants.

Comparing Human and Plant Light Preferences with Various Grow Light Spectrums

Wasted Light Means More Heat

So how does all this light plants can't use affect them, if they are't using it to grow? Any light that isn't reflected is absorbed and turned into heat, warming up the leaves, which affects how the plants grow. Our experiments show that the wasted light colors from commonly-used HPS grow lights can keep leaves 10-25 °F warmer than the ambient air temperature, depending on plant type.

Leaf Surface Temperature Affects Growth

Plants grow best when their leaves are at a specific temperature, as the metabolic reactions proceed best at a particular temperature. If the leaves are too cold or too warm, these reactions are slowed down and the plant won't grow as well. Things like the plant type and CO₂ supplementation affect what the ideal leaf surface temperature is, but if the leaves are cooler or warmer than this ideal, the plant won't grow as well as it could.

Most indoor gardeners know that they need to keep the air temperature in a specific range to get the best performance from their plants. Growers have figured out the ideal ambient air temperature through years of experimentation, all done with grow lights that were actually designed for humans. So, if the ideal air temperature for growing a plant under HPS is known to be 75 °F, its ideal leaf surface temperature is actually significantly warmer than that.

Black Dog LED Grow Lights are Designed for Plants, not Humans-- and that Affects Ideal Growing Conditions

Single-color LEDs allow complete control over the colors (spectrum) of light produced. By combining the right colors in the right ratio to create our plant-optimized Phyto-Genesis Spectrum™, we can give plants all the light they crave without wasting energy on light they can't use. Even though the Phyto-Genesis Spectrum™ is a "full spectrum" grow light in that it has every visible color in the spectrum, the light doesn't look white to us because it has less of the colors are eyes are most sensitive to-- the colors plants don't use much.

Without the colors of light that plants can't use heating up the leaves, the leaf surface temperature is lower compared to the ambient air temperature than with other artificial lights.

To get the ideal leaf surface temperature when growing under Black Dog LED grow lights, the ambient air temperature in the room must be higher than if you were growing with another artificial light.

What Does this Mean for Growing with LED Grow Lights Optimized for Plants?

• In side-by-side tests with the same air temperature, the plants under Black Dog LED's Phyto-Genesis Spectrum™ aren't as warm as they need to be for optimal growth.
  
  For example, most growers aim for a 75 °F air temperature when growing Cannabis under HPS lights without CO₂ supplementation, which results in a leaf surface temperature of about 88 °F. In a 75 °F room under Black Dog LED grow lights, Cannabis leaf surface temperature is only 81 °F, too low for the plants to be performing their best. In order to get the desirable 88 °F leaf surface temperature with the Phyto-Genesis Spectrum™, the ambient air temperature in the room needs to be 84-85 °F. To fairly test the lights on their merits, different ambient air temperatures are required for each type of grow light.
  
  Failure to adjust the ambient air temperature would be like growing Cannabis under HPS at 65 °F: it is just too cold.
• You don't need to ventilate or cool grow rooms powered by Black Dog LED grow lights as much as you would need to with other grow lights.
  
  Excess heat is one of the most common issues indoor gardeners have to deal with. By allowing plants to achieve their full potential at warmer ambient air temperatures, Black Dog LED grow lights can eliminate the need for cooling in many small setups, and greatly reduce the need for it in larger operations. This saves you money in cooling equipment sizing and operating costs. If you're supplementing CO₂, eliminating or reducing ventilation will save on your CO₂ bill.

But I'm Growing in a Cold Area and Rely on the Heat From my Grow Lights?

Using electricity to generate light to warm up your plants is about the least-efficient and most-costly way of warming up your growing environment. If you're using artificial grow lights exclusively, the cheapest option is simply to insulate your grow room better. For greenhouse growing with supplemental artificial lights, natural gas or propane heaters are much less expensive to run than using electric heaters.

Learn More

For a more in-depth discussion of how different artificial lights affect leaf surface temperature, see the full article here.