How to tell the difference between Metal Halide and High Pressure Sodium Growlights.
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How to tell the difference between a Metal Halide Lamp and
a High Pressure Sodium Lamp in a Grow Light
continued
The shape of the lamp alone often shows the difference between a Metal Halide
and a High Pressure Sodium--but not always. There are a class of lamps
called "conversion bulbs". These are lamps which are specially built to burn in one kind of fixture, but give out the color spectrum of the other kind of lamp.
The key to telling the difference is to look at the glass tube inside the
outer glass tube. All High Pressure Sodium Lamps have a thin frosted
glass tube inside. Metal Halide lamps have a larger tube, usually clear,
sometimes bent or curved inside.
If there is a small pin on the side of the metal screw threaded base, then the lamp is a Metal Halide. More specifically, it is a Metal Halide lamp built to burn in the horizontal position. Often it is stamped "HOR" on the glass. The small pin locks into a special mogul sized base with a cut out to position the lamp. The mogul size is larger than the ordinary socket for household screw in lightbulbs.
All High Pressure Sodium Lamps are "Universal" or built to burn in any position.
