Halogen Headlights

The first type of headlights were on the historical cart and horses these were candle powered lanterns.
To be seen and not see oneself. 
It did improve with oil and then oxy acetylene gas powered lighting. Later came the ingeniously electric powered headlamps originally they were sealed beam units which meant when they failed you replaced the whole headlamp. Later came the replacement bulb type which we still use today.
Electric powered bulbs give very high performance for their size and this is enhanced by using chrome headlamp casings combined with glass or Perspex lenses which are patterned to enhance the light direction and give best performance where required. In front of your car and pointing downward.

In the UK the headlamps are positioned with their aim slightly left and the light pattern is a flat one with an upward lift to the left. This is only used to help stop oncoming traffic being severely dazzled by the strong light output. 

Below is a diagram with the yellow area as the beam omitted from a normal UK headlight.

Halogen headlights basically are a bulb which has an electric power passed through a tungsten wire attached to the two electrodes. These electrodes and tungsten wire are encapsulated within a glass bulb filled with halogen gas. 
The gas prevents the tungsten wire burning quickly and hence give long life performance.

There are many different types of bulb but the most common are single and twin filament. The single filament is sometimes used for spot lights. As it suggests the single filament has only one filament but the twin powers both normal and high beam.

Single filamment bulb. Twin filament bulb.

The halogen bulbs are recommended not to be touched with naked skin on the glass. this is because the bulb burns very hot and any skin or oil deposits can cause the bulb to fail due to hot spots where it has had deposits left.


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