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.
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 don't 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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A partner in a thriving retail hydroponics supply business, Rickie Haughton is the owner of hydroponics-gardening-information.com/">hydroponics-gardening-information.com which aims to cater for all levels of expertise in the field of hydroponics gardening. The website is packed with good content about all aspects off hydroponics gardening and offers a free newsletter to all subscribers.