There are basically three types of grow lights used in horticulture. These are:

• High Intensity Discharge Lights. (HID) These come in two types, the Metal Halide Grow Light(MH) and the High Pressure Sodium Grow Light (HPS)

  Metal Halide.
  Metal halide bulbs are designed for plants during their growing cycle. That is, for non-fruiting or non-blooming plants. Metal halide lighting is therefore the best HID choice for the plants growing phase.

  High Pressure Sodium Lights.
  The HPS grow light is used primarily for plants that are in their blooming or fruiting phase. Modern high pressure sodium lighting can, however, be bought, which is enhanced for blue spectrum (for vegetative growth) and for red spectrum (for flowering growth). This means that they can be used throughout the entire growing process for most types of plant.

  Dual light Systems.
  For optimal performance, switchable systems (400 watt and 1000 watt) and dual light systems (250 watt MH + 250 watt HPS giving 500 watt output, 400 watt MH + 400 watt HPS giving 800 watt output and 400 watt MH + 600 watt HPS giving 1000 watt output) are available. This type of grow light system gives the best all round lighting choice.

• Mercury Vapour Lamps.
  Phosphorous coated to promote both blue and red spectrums these lamps are suitable for both the growing and blooming stages of plant growth. They give off more blue light that red and are a cheap way to get started, however the lamp wants replacing every nine months as it can become volatile. Mercury vapour lights cost more to run and maintain compared to HPS, MH or fluorescents.

• Fluorescent Grow Lights.
  These lights emit less light than high intensity discharge lights and although they can be used throughout the plant cycle their lack of brightness will produce small yields. The light produced tends to be softer and less damaging to tender young plants. For this reason, the fluorescent grow light is popular for seedlings and cuttings, an excellent way to establish young plants.

• Ballasts.
  All of the above types of lights use some kind of a ballast system. The one most people are familiar with is the fluorescent light. This has, a small, built in, ballast. It allows the fluorescent tube to build up enough energy to strike, and excite the molecules within the tube, causing light to be given off.

  Metal Halide and HPS grow lights are usually run from remote ballasts. These are external boxes containing the electronics to pre-heat and run the lamp. The ballast is connected to the lamp holder and to the mains power supply. Each ballast used is rated for the lamp wattage and so it is necessary to have different ballasts available for each of the different values of lamp to be used. HID bulbs should be replaced after 12 to 18 months of use. Although HID lamps will continue to light beyond 18 months of use, they will have lost up to 30 percent or more of their lumen output while consuming the same amount of electricity.

  Mercury Vapour Lights. Most of these lamps, up to a value of 500 watts, require no additional ballast. You just screw them into the lamp holder supplied with your equipment.

  N.B.

  Here is a word of warning about lighting.

  There are an awful lot of companies out there selling lights for the hydroponics enthusiast. As in all walks of life, there are good and bad suppliers and manufacturers of lighting equipment. Always look for equipment made by a reputable company and backed by an official testing scheme. (For example the C E mark in Europe means that the article is up to European standards of safety and quality).

  Cheap, nasty, home made, dangerous lights have dogged the hydroponics market for some years. There are these kinds of light and there are well built, professional grade, horticultural lights on today's market. The first are often death traps, being cobbled together from the cheapest, obsolete, end of the line components that are usually mismatched and wrongly configured.

  To think that these poorly built, badly wired, misconfigured lights are being fitted in damp, humid and sometimes even wet, grow rooms is a very scary thought indeed. The installation of these poor quality, dangerous, lights in your home, where your family lives and plays, is always a very grave risk. All this in the name of a bargain!

  So dont risk your own life or the lives of those who live with you. Buy from a reputable source! Lighting is possibly the most important decision for indoor horticulture, cheap normally represents a health risk. For the sake of saving a relatively small amount of money, is it really worth it?

  You have been warned!

  Copyright (C) 2004, 2005 J R Haughton.
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