Lighting is the most important factor in indoor gardening, and often
the biggest financial investment. Outdoors, the sun provides more than
enough light energy for plants, but growing seasons and conditions vary
widely in different parts of the country. Plus, many people simply don't
have the space for an outdoor garden. As long as you have adequate light,
an indoor garden can provide you with fruits, vegetables and herbs year
round...regardless of what is happening outside.
Types of Grow Lights
The main types of lighting for indoor gardens are fluorescent and high
intensity discharge (HID).
Fluorescent lights are excellent for starting seeds or rooting clones.
Fixtures and bulbs are inexpensive, and the low heat output lets you
put them just inches away from your delicate plants. The disadvantage
of fluorescent bulbs is the low light intensity--they can grow a plant
that is 8-10" tall but then the light simply can't penetrate any
further. If the plant grows taller and you keep raising the bulb, lower
sections of the plant will not receive adequate light. Using a "full
spectrum" fluorescent bulb will give your plants all the necessary
wavelengths of light.
High Intensity Discharge (HID)
High Intensity Discharge, or HID, lights have revolutionized the indoor
gardening industry in the last 20 years. These bulbs require special
ballasts (transformers) and sockets to operate. Many types of light
bulbs fall into the HID category, but the two best choices for plant
growth and maintenance are Metal Halide and High Pressure Sodium.
Metal Halide (MH)
Metal Halide lamps are the best single source of artificial light
for indoor gardening. Their balanced light spectrum, similar to the
tropical sun, contains the important blue and red wavelengths that
plants need for rapid growth. You can grow your plants from start
to finish under a metal halide lighting system. MH lamps come in
175, 250, 400, and 1000 watt sizes.
High Pressure Sodium (HPS)
High Pressure Sodium lamps emit light which is heavily concentrated
in the red and orange region of the spectrum. This heavy red light
promotes excellent fruit or flower production (as much as 30% more
than a metal halide lamp), but the lack of blue spectrum light can
sometimes make a plant stretch or become "leggy" during
the vegetative growth stage. This type of light is ideal for supplementing
sunlight in a greenhouse or sunroom. A High Pressure Sodium system
is the most efficient HID light because it has the highest number
of lumens per watt (roughly 10-15% more than a metal halide bulb
of the same wattage.) HPS lamps come in 150, 250, 400, 600, and 1000
watt sizes. The ideal lighting system would include both a Metal
Halide and a High Pressure Sodium lamp. This would produce extremely
fast growth as well as increase flowering by 40 percent. To avoid
the expense of purchasing two separate lighting systems you can use
a conversion bulb.
High Pressure Sodium Conversion bulbs are specially designed to run
off a Metal Halide ballast but they put out more lumens, more red spectrum
light, and they run off less electricity. Start your crop under the
MH bulb and then switch to the HPS conversion bulb when it's time for
flowering. Bulbs that convert MH into HPS come in 175, 250, 400, and
1000 watt sizes. Metal Halide Conversion bulbs allow you to take the
opposite approach: grow your plants under the conversion bulb during
the vegetative stage, then switch to your regular high pressure sodium
bulb for flowering. HPS to MH conversions are only offered in the 250,
400, and 1000 watt sizes. If you only want to deal with one bulb through
all stages of growth, another option is to use an enhanced or "corrected" bulb.
High Pressure Sodium Son Agro bulbs are engineered to provide 30% more
blue spectrum light than a standard HPS bulb. These are available in
160, 270, or 430 watts. Agrosun Halide bulbs, exclusively from Hydrofarm,
are engineered to provide more red spectrum light than a standard halide
bulb. The Agrosun Classic provides 38% more red light, and the Agrosun
Gold provides 49% more red light. These are available in 175, 250,
400, or 1000 watts.
Replace metal halide bulbs after 1 to 1 1/2 years of use, and replace
high pressure sodium bulbs after 1 1/2 to 2 years of use. The bulbs will
continue to light beyond this point but have lost as much as 30% of their
lumen output while still consuming the same amount of electricity. When
replacing your bulb, it is critical to get the right one for your ballast
and reflector configuration.
You can use an automatic light mover to increase the coverage area
and efficiency of your light without using any more electricity. Since
the light is always in motion and does not rest above any part of the
garden, you can move the light closer to the plants and take advantage
of maximum light intensity. As the reflector moves, it directs light
into the garden at many different angles, giving you excellent penetration
through the plant canopy and ensuring strong development at lower levels.
AHL carries a variety of linear and circular light movers to accommodate
almost any garden.
Another way to get the most from your light is to hang reflective Mylar
around the sides of your garden. This highly reflective polyester film
redirects light back to the plants instead of absorbing and wasting it.
This salvaged light often strikes the plants at a different angle, helping
to increase the efficiency and penetration of a stationary grow light.
Mylar can be as much as 98% reflective, while flat white paint is only