While LEDs are full spectrum. They use a blue LED. Blue LEDs are more efficient than red or green ones. But they were really hard to invent. And, only with a phosphorus coating can they create a white LED.
At first, blue LEDS were also expensive to make. But since there is a need for mass-production of white LEDs, they became much cheaper though economy of scale.
Since blue LEDs are very efficient at creating light energy, the energy loss from the phosphorus coating is not that big of a deal.
You may have the notion that LEDs create just a narrow wave length of light. Which is true, but not for the white LEDs. Which makes white LEDs more full spectrum than many traditional lamps, because fluorescent bulbs had narrower peaks, and not a smooth full spectrum. An incandescent bulb also has this, but who uses a 100 watt incandescent bulb in 2025?
There's actually some cool videos about the story of the blue LED.
Grow lights tune the spectrum by adding some red LEDs. They are less efficient in creating light energy out of electricity. But it turns out that plants don't care about the energy level of a photon. Blue photons have more energy than red photons. But red photons have enough to do photosynthesis. Which is why for photosynthetic efficiency, blue light is less efficient.
