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 As
a rule of thumb we recommend that lamps are replaced every 12
months. After 14 months there is an appreciable drop in lumen
output leading to a loss in crop yield.
HPS (High
Pressure Sodium) bulbs are the most
efficient bulbs that are available for grow
lights. They are high in the red and yellow
parts of the light spectrum and low in the
blue, this imitates the autumn sunset.
Because of this spectrum some plants that
are grown with HPS (High Pressure Sodium)
lights can grow elongated and rather leggy,
while many other plants are not affected by
the limited light spectrum. For plants that
normally bud and flower in the fall an HPS
(High Pressure Sodium) is usually the light
of choice because it's light spectrum
promotes flower production. Usually, plants
that produce fruits or flowers will require
18 hours a day of blue spectrum (metal
halide) lighting in the growing phase and 12
hours a day of orange lighting (high
pressure sodium) in the flowering phase.
Metal Halide bulbs are in the white/blue spectrum which
emulates bright summer sunlight and promotes short, compact
growth in plants. They are normally used in the vegetative
period with the user switching to sodium bulbs in the flowering
period. Some larger growers use the ratio of three sodium bulbs
to one metal halide bulb in the flowering period to achieve a
wider light spectrum and claim that this method achieve larger
yields.
Metal Halide Bulbs arc tubes are filled with argon gas which
allow the arc to start easily, This allows the small arc to jump
across the starting electrodes. The small arc heats a drop of
mercury that then vaporizes in the arc tube. When there is
enough mercury gas, the main arc lights up.
Metal Halide Bulbs are only rated for 10,000 hours and should
be replaced every twelve months as the MH arc tube slowly etches
itself into the quartz tube over time and blackens it. As the
metal disappears into the quartz tube, it supplies less gas for
the arc to ionize, and so less light is produced and the PAR and
the lumens drop off.
Grolux bulbs are sodium bulbs that contain 15% more blue than
a standard sodium which allows you to use them through both the
growing and flowering periods.
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