If you want to grow all-year-round, in many
climates it will be necessary to grow indoors under artificial lighting.
This requires careful practice because it is difficult to replicate the
performance of sunlight.
following equipment is required for artificial lighting (see
Depending on the application, either High Intensity Discharge lamps (HID)
or fluorescent lamps are typically used for indoor growing (Fig 4.1).
This is used to ignite then regulate current to the lamp (Fig 4.2).
Ballasts are broadly categorized as either digital, electronic or
magnetic. This choice can have a large impact on the longevity, efficiency
and output of lamps.
- Shade (or
require a shade to direct light towards the plants. This usually
incorporates the lamp holder or socket.
This is needed to switch the lamps on and off.
occurs within the visible light spectrum, wavelength range 400 to 700nm.
Within this range, 445nm (blue) and 650nm (red) are needed most.
HID’s are generally used for the vegetative and flowering/ fruiting phases
of heavily fruiting plants. Their popularity is due to their high lumen
per watt rating. They produce ~5 times as many lumens per watt than
The following types of HID
are commonly used:
MH lamps produce light that
is predominantly ‘blue’ in color. Blue light is ideal for producing strong
vegetative growth such as larger leaves and thicker stems. MH is
also ideal for producing shorter, dense plants which have shorter
internodal spacing. Plants of this shape utilize light more efficiently.
High Pressure Sodium (HPS):
HPS lamps produce more
‘red’ light. Red light promotes flower onset and fruit production. HPS is
therefore more suited to the flowering/ fruiting phase.
Unfortunately, MH and HPS
lamps each require a different ballast and lamp holder. Due to this
expense, it is common practice to use a HPS lamp for both vegetative and
flowering. This is particularly common if plants have a very short
vegetative phase. However, as a general rule, the use of a HPS lamp
throughout can promote tall and spindly growth.
Blended light lamps:
To prevent the need for a
separate lamp kit for both the vegetative (MH) and flowering (HPS) phases,
“blended light” lamps are available. These produce a more balanced
spectrum of ‘red’ and ‘blue’ light.
Fluorescent lamps produce
less lumens per watt compared to HID lamps. Hence, their use is limited to
plants needing low to medium light intensities, such as seedlings, clones,
herbs, orchids and lettuce. Unlike HID lamps, they generate minimal heat
and therefore require little or no ventilation.
Fluorescent lamps are
broadly categorized as either ‘strip’ fluorescents (SL) or ‘compact’
fluorescents (CFL). They are available in different wattages and color
temperatures. Those of high color temperature (known as “cool white”) are
more ‘blue’ in color and suited to vegetative growth and the development
of seedlings and clones. Fluorescent lamps with lower color temperatures
(“warm white”), are redder in color and therefore better for flowering.
CFL’s are generally available in higher wattages than SL’s and are
therefore suitable for plant species needing higher light intensities.