a hormone during the dark period (night in
nature) which induces the start of the
reproductive (flowering) cycle. When the
hormone builds up to a critical level, flower
growth commences. The number of hours
of darkness required to induce flowering
differs for each variety.
Gardeners have a choice of lamps to
illuminate their garden. Incandescents,
tungsten-halogen lamps and screw in "grow
bulbs" are inefficient sources of light.
Although they are inexpensive to purchase,
their cost of operation makes them the
costliest source of light.
FLUORESCENTS
Until the early 1980’s most indoor
growers used fluorescent lights to illuminate
the garden. These tubes have tremendous
advantages over screw-in incandescent
lights. A fluorescent tube emits about 3
times as much light as an incandescent of
the same wattage and has a light spectrum
that plants can use more efficiently.
Fluorescents have their limitations.
Light is emitted over a large area, the entire
surface of the tube, so it is not
concentrated. Because the tubes are bulky
only a limited amount of light can be
delivered to a given area. The fixtures are
usually placed within inches of the plants so
that the light does not spread and become
less intense. When the light fixtures are
hung they are hard to manipulate and make
it more difficult to tend the garden.
Standard fluorescents have an
efficiency of about 30%. Seventy percent of