What is the optimal wavelength of light for growing plants (cacti indoors in a northern illinois climate)?

Oz Oz at upthorpe.demon.co.uk
Tue Oct 14 10:19:25 EST 1997


In article <344366CE.3295FDDB at 127.0.0.1>, Jan Andersen <root at 127.0.0.1>
writes
>2) All (nearly) flourescent tubes are made with mercury gas inside - this
>produces
>ultraviolet light, which is converted to visible light by means of an emulsion
>at the
>inside of the tube - a 'gro-light' has in addition to that a filter that takes
>away some
>wavelengths, which by necessity means that a 'gro-light' tube is less efficient
>than
>one without filter.

This need not be the case. There are a very large number of fluorescent
phosphors able to change UV to a wide variety of different colours. A
conventional CRT colour monitor has three different ones, but there are
very many. A *properly designed* gro-light should have high efficiency
phosphors designed to match the plant requirements nearly exactly and
require no filter.

You also stated that chlorophyll did not require any red to function.
This was the generally held view, however I am pretty sure that I
remember a paper (long time ago) that showed higher efficiency when red
was also included. IIRC chlorophyll activated by red light could absorb
blues of a lower frequency than when not, widening the available
spectrum that could produce the first stage in the relevent biochemical
cycle.

However I have some old tube spectral outputs. Let's see.

efficiency (in strange units)
        continuous spectrum     Peaks: output at wavelength
        400   500   600   650   <<(wavelength nm)
Grolux   50    70    10   700   200 at 410, 400 at 440, 250 at 550
Daylight 20    70    70    70    70 at 380, 110 at 410, 260 at 430, 150 at 550
Tropical 20    70    70    30   110 at 410, 230 at 430, 160 at 550

So it looks to me as if grolux are more efficient, and appear to have
had their spectrum carefully tailored. Given the hi-tech nature of
modern greenhouse growers and labs that use them, I would be surprised
if gro-lux type tubes do not offer significant advantages over
conventional tubes.

-- 
'Oz     "Is it better to seem ignorant and learn,
         - or seem wise and stay ignorant?"



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