Headlamp Focus - Real World Example


There have been many exchanges the past regarding headlamp reflectors, focusing, brightness, etc. This led me to do a little project that was a bit more involved than expected! It seemed reasonable to me that the information would be of more value to the masses if we showed HOW headlamp focusing affects you and skip the how it works part. What follows is my attempt to accomplish that.


The photo above was taken of the light projected on a large sheet of cardboard positioned 5-1/2' in front of my right headlamp. As noted in the photo the first column is without the lens in place to refract or spread the light. The second or right column shows the same focus with the lens in place.

Position #1 - The bulb or filament is adjusted with the screw as loose as possible allowing the bulb to move forward or closer to the lens. What is happening here is only a percentage of the reflector is in use. The functional portion of the reflector is aiming the light in a tight or small circle. This means that only the center portion of the lens is receiving concentrated light to refract or spread. The circle is 12-13" in diameter or slightly larger than the headlamp.

Position #2 - The bulb is at or near it's focal point at 1-1/4". It shows a full concentration of light in the same 12-13" circle. With the lens in place it leaves a fairly sharp line or contrast across the top of the pattern.

Position #3 - The bulb is pulled rearward tight with focusing screw. Again, only a portion of the reflector is useful. The light is being reflected outward. There is a LARGE dead spot in the center. Note the direct light from the bulb is not concentrated enough to provide any direct "fill". The light rays are concentrated or directed to the outer portion of the lens at an angle that can't even refract appropriately. The circle is large!


The point of this is the significance of focusing the lamps. No matter how bright your headlamps are you will at least have dead spots if unfocused. At worst you will be blinding other drivers on the road with the uncontrolled light rays. Please note the focusing is done with high beams on. Obviously the early "H" lamps are focused with the driving lights on (no low or high beams present).

A comparison photo from John Brady (above) shows an overlay of a reproduction reflector over an original reflector. The reproduction shows a much shallower dish or parabola. If the shape is a true parabola (questionable) it should function fine with a couple caveats. First, the focal point will be greater than the original 1-1/4" from the rearmost surface. It may require both a longer focusing screws and spring as well as other modifications to allow the light socket to move forward far enough to focus. In John's case I think his special halogen bulbs were longer and may help compensate for this somewhat.

Brightness a Separate Issue

Proper focus will give you the brightest lights possible with your given configuration. Beyond that you must have good electrical grounding throughout (easy to test) and good electrical contacts at all points. Chrome reflectors will inhibit efficiency. With 50 cp. bulbs chrome reflectors will produce the estimated equivalent of 25 cp. used with silver or special aluminum coatings. There are other alternatives to side step some of these issues such as halogen lights with alternator which may be preferable to some restorers. Which ever your choice Don't forget about the focus!

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©1998 Marco Tahtaras