High Intensity Discharge

Among this category of lighting sources are Metal Halide (MH), High Pressure Sodium (HPS), and Mercury Vapor (MV) systems.  These sources have been chosen for several years because of their high lumen output.  Unfortunately, there are several drawbacks to choosing HID lamps.

While their initial light output is very high, the lamps depreciate quickly, with HPS losing 19% output and MH losing 40% output after 10,000 hours.  Along with the severe light loss, the rated life of most HID lamps is only 20,000 hours.  This amounts to a little over 2 years of constant burn time before replacement.

Another major downside to HID lamps is their sensitivity to vibration and weather.  The electrode inside each lamp is susceptible to breaking when exposed to constant movement (i.e. street light pole on a windy day).  Also, the electrode becomes more brittle in lower temperatures, which lends itself to fracture.

Additionally, while the lumen output is very high, there is a color shift of the light.  HPS lamps usually produce a yellow light, while MH lamps produce a Blue/Purple light.  This color shift is measured by the Color Rendering Index (CRI).  A chart of the CRI of multiple products is available on our Quantitative Comparison page.

Finally, safety is a problem with HID lamps.  Temperatures can reach 1100°C in some lamps and are under extremely high pressures.  When the lamp breaks, it explodes, propelling extremely hot and sharp particles of glass over a large area.  Also, fixtures for these lamps must be rated to contain the fragments if the lamp were to rupture, which means increased price.

While HID lamps have served their purpose well, they have been surpassed by new technology, notably Fluorescent, Induction, and LEDs.  Click here to learn about Fluorescent.

Disclaimer: Information about high intensity discharge lamps has been taken from published catalogs, discussions with lighting end-users, and personal professional experience.  This page is to allow for points of discussion, not points for debate.  For more detailed information about high intensity discharge lamps, please contact the manufacturer.