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Why do we include ultraviolet (UV) in our LED grow light spectrum?


Ultraviolet (UV) light has a wavelength shorter than 400nm and contains more energy per photon than light in the 400-700nm Photosynthetic Active Radiation (PAR) region of the spectrum.

There are plenty of reasons to leave UV light out of an LED grow light. UV LEDs cost 10 times more than LEDs in the PAR region of the spectrum. UV light doesn't count toward PAR / PPFD measurements. And because UV photons are more energetic than PAR photons, it takes more electricity to create them- we get fewer photons per watt out of our UV LEDs than we do out of any other color LED we use.

In other words, if we replaced our UV LEDs with other LEDs in the PAR spectrum, our lights could be made cheaper and our PAR measurement statistics would look even better on paper. So why do we bother to include UV in our LED grow lights?

At Black Dog LED we believe in making lights that provide the best possible grow results, rather than lights that look good on paper. Ultraviolet light grows higher-quality plants and increases canopy penetration, so we include it in our spectrum.

UV light stimulates several different photomorphogenic responses in plants. Plants exposed to UV light create higher levels of natural sunscreen compounds, such as terpenes, antioxidants, flavonoids, THC, CBD and vitamins. Trichomes are also a natural mechanism for providing protection from UV light, so plants produce more trichomes containing these natural sunscreen compounds when exposed to UV. By including UV in our spectrum, we grow higher-quality plants with richer qualities of what you're growing the plants for.

UV grow lights for plants also help increase canopy penetration, allowing for more productive plants as well. Although UV light does not count toward PAR directly, it helps deliver more PAR-spectrum photons lower into the plant canopy. Plants are incredibly inefficient at capturing and converting PAR light into energy that they can use. Most plants only utilize 3-4% of the photons that hit each leaf. Some photons pass through leaves completely, while many others "bounce" off molecules in the leaf and are not successfully captured and used for photosynthesis. These "bouncing" photons typically lose a little bit of energy each time they bounce, which shifts their color more toward the red end of the spectrum, and towards a longer wavelength. For example, if a 660nm red photon bounces inside a leaf on its way through, it would lose a little energy and may become a 750nm infrared photon, and therefore no longer directly usable for photosynthesis (but still possibly helpful due to the Emerson Effect). A photon starting at the top of the canopy as a 440nm blue photon may degrade to a 520nm green photon on its first bounce, then to a 600nm orange, then to a 660nm red, giving it more chances to be successfully absorbed and utilized for photosynthesis on its way through multiple leaves in the plant canopy. Because UV photons start with even more energy (and a shorter wavelength), they pass through more leaves in the canopy before degrading to an energy level the plant can no longer use.

Ultraviolet light increases plant quality and helps deliver more PAR to lower leaves, even in dense plant canopies. That is why we include substantial amounts of UV light in our spectrum. It lowers our photon flux efficiency numbers but actually helps grow better plants. Some competitors claim to have UV in their spectrum, but they don't quantify how much they produce, because it is a trivial amount.

Growing with UV light costs a little more, but we're sure you will agree that the better actual growing results are worth it!