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Comment by tifik | Hacker News Reader

I don't think we currently know of any practical way to _arbitrarily_ change the wavelength and frequency of electromagnetic waves (within the same medium), and even if there was, it would likely take so much energy that it would never be efficient to spend the energy this way.

Somehow submerging the plants within a different medium to change the entire spectrum would also likely not achieve any gains either, because by doing that you can only reduce the total amount of energy in any part of the spectrum, not shift it elsewhere (afaik).

edit: added 'arbitrarily' - as replies point out, moving towards the lower-energy end of the spectrum is not hard.

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Fluorescence is pretty easy and cheap, we use it all the time. Yellow fluorescent material is added to blue LEDs to make white LEDs; blue fluorescent material is added to paper, clothing, and laundry detergent to make whites appear brighter under UV light.

Shifting frequency the other direction is much harder; some materials exist that can double the frequency of light (known as second harmonic generation), but it's not as cheap as fluorescence. They are used in green laser pointers to turn infrared light into green light.

> I don't think we currently know of any practical way to change the wavelength and frequency of electromagnetic waves (within the same medium), and even if there was, it would likely take so much energy that it would never be efficient to spend the energy this way.

Isn't this the entire principle behind using quantum dots in displays?

i.e. The quantum dots absorb light from the backlight and then re-emit it as a very specific color band.

What? Yes we do. It's called fluorescence.

If you find a color range not being used effectively, it's easy to drop the frequency down to a better one.

Sorry, I should have written 'practical way to arbitrarily change...'. One of the sibling comments to yours touches on the topic of increasing the frequency, which is what I was getting at with the practicality and energy consumption.

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