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

Bart Z. Lederman lederman at star.enet.dec.DISABLE-JUNK-EMAIL.com
Tue Oct 14 14:26:39 EST 1997

In article <61vlk3$6k5$2 at news.NetVision.net.il>, Stan Goodman <sgoodman at netvision.net.il> (Stan Goodman) writes:
>In message <pspopeXSPM-1310971949310001 at> -
>pspopeXSPM at shopchicago.com (Scott) writes:
>I am trying to accelerate the growth of my baby cacti by increasing their
>light exposure with fluorescent lamps.  I am wondering what would the
>Plants, for the most part, are uninterested in red and infra-red radiation.
>They do their photosynthesis thing with the light from the sun; in order to do

I used to grow plants under lights, and have read many reference books
(and even own a few), and all of them indicate that the above statement
is wrong.  Plants are sensitive to red and near infrared.

The balance between shorter and longer wavelengths (plants are relatively
insensitive to green) will have an effect on how the plant grows.  Too
much of one or the other will cause the plant either to be very short
and 'stocky' or very long and 'gangly'.  At the moment, however, I
don't remember which excess causes which effect.

The so called 'plant lights', which give off purple (actually magenta)
light may make your plants look nice, but they tend not to be very
efficient compared with regular fluorescents.  However, fluorescents
tend not to have enough red and near infra-red compared with daylight.
Of course, flourescents have been greately improved in the past few
decades, but I suggest doing what most of the better books I've read
on the subject recommend.  This is to use the most efficient normal
white flourescents you can get that are on the 'cool' side (used to
be 'cool white'), and add 10% of the wattage in incandescents to
make up the missing red and near-infrared.  So if you are using
four 40 watt CW lamps, you would add about 16 watts of incandescent,
or say two 7 or 10 watt lamps.

Keep in mind that many plants are very sensitive to the ratio of light
to dark that they get, and if you give them too much light or too little
light in each 24 hour cycle you won't get optimum results.

 B. Z. Lederman   Personal Opinions Only

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