In article ,
Ron wrote:
I read about some NASA experiments with blue and red LED's for growing
vegetables in space.

Anyone here who has experience with this?

In times when everybody is complaining about the price of electricity it
seems natural to think about replacing all kinds of lamps with LED's.

But then there is the question of effeciency and wave lenghts.

I read that in principle plants only need blue and red light to grow and
prosper. If I remember correctly it was 450 nm and 675 nm light that was
most suitable.

But what about IR and UV? No other wave lenght? Plants don't need that at
all?

Many plants use the shifting balance between 'red' and 'far-red', i.e.
near IR to 'measure' day length and 'decide' when to initiate flowering.
For vegetative growth, most plants have auxiliary pigments that let them
get substantial benefit from wavelengths outside those that chlorophyll
is most responsive to. This is especially apparent in aquatic plants that
usually grow in water tinted brown or yellow, and in understory
plants that get heavily filtered light. So to some extent, it's
the total amount of light, more than the frequencies, that counts.

And if this information is correct, what is the right balance between those
2 components. I have seen conflicting information. In one case they said the
red-blue ratio should be 3:1, while others say almost the opposite.

Depends on the plant, and whether you're after vegetative growth or
flowering. People grow plants under all kinds of artificial light
with considerable success. I grow all the transplants for my garden
under cool white fluorescents, which have a terrible spectrum --
mostly green wavelengths, although they look white to the eye, and
they do very well -- as well or better than with the 'plant lights',
expensive fluorescents that mainly emit blue and red wavelengths.
Commercial growers use sodium and metal halide lamps, which also
have skewed spectra.

I want to run some small tests with some very fast growing plants,
preferably edible. Any suggestions what vegetable/herb would be most
suitable?

I'd suggest lettuce -- it's fast growing, you don't want it to flower,
and you can eat it. Buttercrunch is a small Bibb type that grows
well under artificial light, at least for me. One winter I grew a
lot under cool whites, just for something to try. Lettuce does best
under cool conditions and doesn't require as much light as many other
edible plants.

I've seen panels of white LEDs, too. They are being used here
experimentally as auxiliary street lights, and they are remarkably
bright. Note that most LED lights these days actually emit UV, and
phosphors are used to create the 'color temperature' or wavelength
pattern, as with fluorescents.

My guess is that LED lighting will replace compact and standard
fluorescents in the fairly near future, once they get marketed to
consumers and economies of scale kick in. I don't know whether
they will replace MH and HPS before or after for commercial growers.

Note that if you want to compare different combinations of blue and
red, you'll have to compensate for different amounts of energy that
actually reaches the plants' surface, since most wavelengths can be
used to some extent, and some phosphors are more efficient than others
in converting UV to the desired wavelength. If the color is produced
by filtering through a colored coating, the difference will be even
more extreme. So a light meter, at least, will be important for
your experiments. You don't want to conclude that one color
combination is better than another when what's actually happening is
that the better combinations are just providing significantly more
total energy than the others.

Good luck, and let us know what you find out!