H.I.D  stands for "High Intensity Discharge"  These are a family of bulbs that produce light by creating an electrical arc inside the bulb.

What are they good for?

They will produce more light for less electricity than any incandescent bulb.  They are naturally bright and powerful and are ideal for lighting large areas.  They can also run for thousands of hours with no maintenance, much longer than any incandescent bulb.  They are indifferent to heat, cold, and vibration.

What are they bad for?

The bulbs are expensive and need separate (also expensive) ballasts to  make them go.  You can't just screw them into any lamp and have them work.  You can't switch around ballasts between different bulbs.  If you are not familiar with electricity you may need to bring in an electrician to do the initial setup.   They may start and restart slowly, requiring a minute or two to come up to full brightness.

The ballast has to push the bulb fairly hard to start it.  This push is is stressful to the bulb.  If you have a situation where your light will be turned on and off many times a day you will not get the full long life out of this kind of bulb. 


There are four basic types:

* Low pressure Sodium

Probably the most efficient bulb money can buy.  Its main drawback is that it produces an ugly pale orange light.  Everything it lights will look pale orange, no matter what its real color is.


* High pressure sodium

Enables you to see a little more color than with low pressure sodium, but at the cost of some efficiency.


* Mercury vapor:

You can see colors, but everything will have a harsh industrial look due to the bluish tint of the light.  These bulbs  are being phased out, so if you are installing a new system you may want to avoid these.


* Metal Halide

The least efficient of the HID lights, but has the most natural color.  The light is a touch greenish.  Is still more efficient that any incandescent bulb.


MY HID light is turning on and off by itself.

This means that the bulb is worn out.  Just put in a new one and you should be fine.


What about for cars?

This is an interesting subject.  Because HID bulbs are so bright, you would think they'd be ideal for cars.  The problem is that if they are not installed perfectly you become a public menace. In the US it is illegal to retrofit an HID bulb into a non-HID housing and then drive on a public road with it.  If you do, you become a cop magnet because it's an easy ticket for them.  In Europe car manufacturers are required to make any HID headlight self leveling and the housing self cleaning so it cannot refract glare at oncoming drivers. 

In the US there are some expensive cars that come with HID headlights.  These have a slight bluish color.  This has led to a trend where people put bluish lights in their car to make them look fancy.  If all you want is bluish headlights, then by all means get them - but don't get real HID bulbs, get an incandescent bulb with a blue tint from any vendor.  You'll have the look you want for only a modest cost.

HID conversion kits are worthless unless they include a new lamp housing to replace your stock one.  The problem with retrofitting HID bulbs into a housing meant for an incandescent bulb, like a halogen bulb,  is that the filament on an incandescent bulb is not the same size and shape as the arc in an HID bulb.  HID lights have housings that are specially designed for them.  If you somehow squeeze an HID light into a non-HID housing you will get a terrible beam pattern that does not light the road evenly, and does not really help you see better.