HID Lights
There four types of commonly used HID (High Intensity Discharge) lamps in hydroponics:
- Metal Halide (MH) The most commonly used kind in indoor horticulture. They emit a full-spectrum sun-like
light (all colours). They have a service life of between 6-9 months, after which time the light output drops by up to
50%.
- High Pressure Sodium (HPS) A lot brighter than MH lamps, they emit mostly a red-orange light.
- Flourescents Provide a full colour spectrum (similar to MH lamps) and emit an evenly distributed soft light
with very little heat. Generally used for rooting clones or smaller plants, as the light is less intensive. Cool White
fluorescents are the most popular for hydroponic indoor growers. Economical to use.
- Conversions Are sodium bulbs that run in MH lights but emit a more balanced spectrum of colour than HPSs.
Less popular due to their expense but their service life is generally 10 times that of MH lamps.
How do they work?
HIDs generate very intense light, enabling plants to photosynthesise at unparalleled rates, increasing growth and
flowering. Requiring ballasts to transform low voltage household currents (240v) into high voltages (480v), a huge
bolt of energy is built up and then fed through the gas filled chambers of the lamp and maintained, creating very
bright light.
What's the difference between Watts and Lumens?
Lumens is a measurement of perceived brightness in the visual spectrum. Watts, in contrast, is a measurement of
lights but not of light itself. For example, a 100w lamp uses 100 watts of electricity to produce the light it emits.
Therefore, there is an efficiency ratio of watts into lumens, and this is a crucial factor regarding horticultural
lights.
So, a typical 100w household bulb can provide about 1,500 lumens, converting each watt into about 15 lumens.
Whereas a standard fluorescent household bulb converts each watt into about 50 lumens. It is therefore a more
efficient light source, providing more light.
At the other end of the scale, HID lamps are a lot more efficient, converting each watt into about 150 lumens.
Plants generally like the most amount of lumens possible. However, lumens diminish the further away the light source
is from the plants. Therefore, theoretically, it would be possible to grow plants under 100w household lamps, but due
to the intense heat produced, particularly from halogens, it is unsuitable to place them very close to your plants.
But, this is only half the story! What about Light Spectrums?
In order to photosynthesise, plants require the full spectrum of light, which extends between two forms of invisible
UV (Ultra Violet ) and IR (Infra Red), incorporating Visible Light between the two. Most lamps only represent about
half of the visible light range, making them less than useful for photosynthesis. In an ideal world of horticultural
lighting, replicating sunlight is the aim, and so it is necessary to span the complete range of light.
White Light fluorescents provide neither of the invisible ranges (UV or IR) but emit a more blue-violet visible
range. Other fluorescents can be bought providing a more warm red visible light, and even uncoated UV fluorescents
are also available today. But, there are no suitable IR fluorescents available, making it impossible to replicate
sunlight for growing purposes.
HPS lamps emit a more warm yellow to IR light spectrum and MH lamps emit a cool blue-violet to UV light range.
In conclusion, fluorescents, due to their affordability, are primarily used for propagating and cloning plants,
whereas a combination of both HPS and MH is the ultimate replication of sunlight to indoor horticulturists and will
produce the healthiest plants with the greatest yields.
I think I understand lights now, but how much light do I need for the space allocated for my Grow Room?
A general rule of thumb is that there is no such thing as too much light for plants to photosynthesise, but the
opposite can apply. If plants do not receive enough light your plants will grow without photosynthesising, making
them 'sparse' and dull, eventually killing them off. This is known as Etiolation. Therefore getting the right amount
of light is paramount to healthy plants.
As a rough guideline, it is generally assumed that when using fluorescent lamps for vegetating and propagating
plants, 50 watts of light per square foot of growing space is ample. For HID lamps, 20 watts per square foot of your
growing area provides enough of the right light spectrum at the correct strength to encourage more vigorous growth and
flowering.
These are, however, rough estimates, and only experience and an interest in how your plants behave to the light
received is recommended!
Finally, temperature and diffusing light in your grow rooms is important as well. Plants will wilt and die under
extreme heat, but diffusing light by reflecting it around the room using reflective sheeting (mylar is recommended)
can only be a good thing.
|
