[Community_garden] light tubes and seed starting

[Jim Flint]

Susan and community garden friends,

A few notes to add on light tubes and seed starting ....

Fast growing seedlings like tomatoes like to stretch to get as
close as possible to their light source. If the light source is
more than one to two inches from the seedlings, the plants are
more likely to become spindly. Keeping the fluorescent lights
close to the plants will help plants to develop stockier stems,
along with periodically rotating the plants under the lights.

>From physics, light intensity (as measured in lumens) decreases
with the square of the distance from the light source. At a
distance of 3 inches from the light source, plants receive 1/9
the light intensity as compared to a distance of 1 inch. At a
distance of four inches, light intensity decreases to 1/16 the
lumens of a distance of 1 inch.

Another factor affecting plant growth is the quality and
spectrum of the light source. Gardeners may remember the
acronymn ROYGBIV, which represents the colors of the light
spectrum (red, orange, yellow, green, blue, indigo, violet.)

In a general sense, the blue portion of the spectrum influences
plant growth, while the red portion influences flowering. Cool
white fluorescent tubes have high light output in the blue
spectrum. Warm white tubes have high light output in the red
spectrum.

Some people recommend using one cool white tube and one warm
white tube per fixture, but a better solution is to use wide
spectrum fluorescent tubes, which have a pink light that
combines high output in the red and blue spectra. Full spectrum
fluorescent tubes are an effective but more expensive choice
that tries to replicate sunlight by balancing out light energy
across the spectrum.

During the past few years, I've tested plant growth with several
light tubes and fixtures, including T-8 light tubes and T-12
tubes. In the tests, the overall most reliable and cost
effective performance in seed starting came from 40-Watt T-12
GroLux Wide Spectrum tubes. A close second in performance were
the full spectrum 32 Watt T-8 tubes. These tubes use 20% less
electrical energy but their smaller diameter (as compared to the
T-12 tubes) resulted in a bit less dispersion of light.

If you're interested in building your own indoor garden with a
T-8 light fixture, I've posted plans on our web site at
http://www.burlingtongardens.org/classic_indoor_garden.html. If
making a homemade unit, look for a light fixture with a larger
reflector and at least 3 inches distance between the tubes. The
greater the dispersion of light, the less rotating of plants to
promote even growth.

Friends of Burlington Gardens sells four models of Vermont
Indoor Gardens with wide spectrum light tubes. The models at
http://www.burlingtongardens.org/IndoorGardens.html have
excellent light fixtures with wide spectrum bulbs, are priced
affordably, and shipped via UPS. Proceeds from indoor garden
sales are used to help develop new community gardens in Vermont.

Seed starting can be great fun, and I hope that many community
gardeners will give it a try.

Jim

Jim Flint, Executive Director
Friends of Burlington Gardens
180 Flynn Ave Studio 3
PO Box 4504
Burlington, VT  05406-4504
802-861-4769
www.burlingtongardens.org


Message: 3
Date: Sat, 31 Mar 2007 06:10:59 -0700 (PDT)
From: Susan Shear <s_shear at yahoo.com>
Subject: Re: [Community_garden] flluorescent bulbs
To: community_garden at list.communitygarden.org
Message-ID: <557634.1016.qm at web31304.mail.mud.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"

I just took a seed starting class at the University of
Connecticut.  The instructor told us that he uses shop lights
that hangs from chains and reguluar flluorescent bulbs.  He said
the key was to keep the light 3" from the top of the seedlings
(thus the need for the chains) because light that is too far
away from the seedlings causes spindly growth.

  - Susan