There are many different names for the same thing: a blue (or very rarely UV) LED diode covered with a yellow phosphor will create what the human eye perceives to be white light. The invention of practical high-intensity blue LEDs earned a Nobel Prize in 2014 because coating them with a yellow phosphor allowed LEDs to replace all other lighting technologies for humans while significantly increasing lifespan and efficiency.

White LEDs work by covering a high-intensity blue LED and placing a phosphor “cap” on top, usually yellow. When a high-energy blue photon generated by a blue LED strikes one of the phosphor molecules, some of its energy is converted into heat and the rest is re-emitted as a different, lower-energy (redder) color of light. Some blue photons sneak through the phosphor layer, but most are converted to a yellow or red color. This allows highly-efficient blue LEDs to recreate most of the colors that our eyes can see at a significant energy savings compared to incandescent, fluorescent / induction, high pressure sodium and metal halide lights.

The phosphor coating converts 20-40% of the light energy produced by the blue LED to heat to make it look white or “broad spectrum” to our eyes. Even so, “white” LEDs are far more efficient than almost any other lighting technology for humans.

However, the colors of light human eyes preferentially see in the green/yellow range of the spectrum are almost opposite what plants preferentially absorb for photosynthesis in the red and blue areas of the spectrum. Combining red and blue LEDs will always create light more efficiently for plant absorption than a phosphor-coated blue LED ever can.

The so-called “broad spectrum” and “full-spectrum” or “white” phosphor-coated blue LEDs are designed to be ideal for human eyes rather than plants; although they include the colors plants require to grow, they can never be as efficient as the right combination of single-color (mostly red and blue) LEDs for growing plants. White LEDs produce more yellow light than plants can efficiently use, and if they are based on a blue LED they lack UV light which increases plant quality.

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