Discover Lighting!

There are three basic types of HID lamps, all operating on the same general principle but producing dramatically different results:

MERCURY
Now has limited use due to its older technology. It has about twice the efficacy of incandescent; however, it has poor to barely acceptable color. Being relatively inexpensive, it is therefore still used where low installed cost is required. Most common application is the familiar “barn light” one can see when traveling country roads at night. One quirk of these lamps is their survivability. They don’t seem to expire like other lamps – they just keep going and going, continually losing light output and changing to a repulsive greenish color. It’s a characteristic similar to old soldiers – they never die, they just fade away!

METAL HALIDE
Developed around 1960, this technology is an outgrowth and improvement of the mercury lamp. The color rendering is improved, with CRI ratings from 65 – 90 and a choice of color temperatures is available. Here’s where metal halide has found a home:

Indoor
Retail stores
Atriums
Warehouses and Industrial facilities
Airport terminals

Outdoor
Street lighting Area Lighting Sports stadiums Parking garages and lots	Building façade lighting Bridges Tunnels Airport exterior gate areas

HIGH PRESSURE SODIUM (HPS)
This variant was developed in the mid-Sixties and is quite different from the previous two. As the name implies, it uses sodium (and mercury) to produce light with a characteristic golden yellow color. If you have ever flown in an airplane over a large city at night, then you have seen HPS (and lots of it!). HPS has the highest efficacy of all popular light sources, but still is limited in use due to its poor color (CRI in the low 20’s). Finding your blue car in a parking lot could be a challenge. Not all applications require good color, so HPS is still quite popular, although as metal halide continually improves, it is taking over some of the jobs from HPS. Where is HPS used?

Indoor
Warehouses
(That’s about it for indoor!)

Outdoor
Street Lighting
Parking garages and lots
Building façade lighting
Area Lighting
Airport exterior gate areas

There are some specialized sources in the HID family that have gone unmentioned, but you should get the drift from this and see that HID provides us with another useful tool in our basket of lighting tricks.