Construction and Operation

Marijuana Horticulture

by Jorge Cervantes

Metal halide lamps produce light by passing or arcing electricity through vaporized argon gas, mercury, thorium iodide, sodium iodide, and scandium diode within the quartz arc tube. After they are in their proper concentrations in the arc tube, the characteristic bright white light is emitted. This process takes about three to five minutes.

The metal halide arc system is very complex and requires a seasoning period of 100 hours operation for all of its components to stabilize. If a power surge occurs and the lamp goes out or is turned off, it will take five to fifteen minutes for the gases inside the arc tube t cool before restarting.

The outer bulb functions as a protective jacket that contains the arc tube and starting mechanism, keeping them in a constant environment as well as absorbing ultraviolet radiation. Protective glasses that filter out ultraviolet rays are a good idea if you spend much time in the grow room, or if you are prone to staring at the HID!

When the lamp is started, incredible voltage is necessary for the initial ionization process to take place. Turning the lamps n and off more than once a day causes unnecessary stress on the HID system and will shorten its life. It is best to start the amp only once a day, and always use a timer.

The metal halides operate most efficiently in a vertical +- 15 degree position. When operated in positions other than +- 15 degrees of vertical, lamp wattage, lumen output, and life decrease; the arc bends, creating non-uniform heating of the arc tube wall, resulting in less efficient operation and shorter life. There are several lamps made to operate in the horizontal or any other position. These bulbs have “HOR” stamped on the crown or base which refers to horizontal.