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

Jan Andersen root at 127.0.0.1
Wed Oct 15 02:49:04 EST 1997


Oz wrote:

> >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.
>

Very interesting. It seems as if you may be right :-) Still, you don't give
any numbers for watt input/lumen gained, and as far as I remember, this
was the interesting thing - the industrial 'cold white' tubes won big here.

A comment about the hi-tech greenhouse growers: they are of course
highly competent in their trade. But this doesn't guarantee that they know
much about this subject - it's like eg. the system administration staff in big
companies - many of them believe firmly that buying eg. Win95 or NT
gives them large administrative advantages over Novell or UNIX. I as
a (IMHO very competent) programmer of all these platforms know it
is not the case. I guess even professionals choose according to their
best knowledge - which isn't necessarily the best there is :-)

So, I'm still not convinced by your arguments.

/jan

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