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Misc: Everything Else Lights


Well Known and Active Website User
VOC Member
I have a light on one of my bikes (not a Vincent) that is a spotlight reflector fitted with a twin filament bulb, to get it to work right I had to set up a rig so I could move the bulb in and out to get the sort of spread I wanted, I ended up about 2mm back from the mount, it's an interesting experiment to try on any reflector as a small change can make a considerable difference to the spread.
Indeed Chris. The formula for focus includes X (squared) which means massive changes of area for very small increments. The size of the globe is also important.


Well Known and Active Website User
VOC Member
Astronomers, particularly optical as opposed to radio etc, should know about mirrors, lenses etc. No one has to know about parabolas, spheroids etc but a simple analogy might help. First, consider the light from a distant source, star, street light or similar. If you use a simple lens to try focus an image of the source you will find that different colours come to a focus at different distances from the lens. The easiest way to understand this is to consider the lens as a collection of prisms, with different angles and we all know what a prism does to light. A parabolic mirror does not have this defect and so a point source of distant light will come to a point image at the focus of the lens. Now imagine this in reverse where one puts a point source of light at the focus of the mirror and the mirror will reflect that as a parallel beam of light. If one was to move the point source of light in or out along the axis of the mirror the beam of light would become either divergent or convergent depending upon whether the light source was moved towards or away from the mirror surface. If the light source is not a point of light but is say a few millimetres diameter, like a typical old fashioned filament lamp, then the mirror will try to make an image of the light source on any distant wall etc, If the light source is moved sideways, i.e. away from the optical axis of the mirror the image will be offset to one side or another. That is why old lamps have two filaments. one as near to the optical axis as possible for the head light beam and one offset both sideways and upwards to produce the dipped beam. Ignore here any effect of a lens in the front of the lamp.
Now, if the light source is not a point, or nearly so, any image produced on the distant wall will be large and spread out. I do not claim to be knowledgeable about all the different types of LED light available. For all I know there are now some very small and very bright ones which will produce a decently focused beam. The ones I have seen, which have large LEDs simply cannot produce a sharp beam. Think of it as the point source being moved around and the resulting image also moving. Then there is the problem of incorporating another LED source, near to but offset from the first one, to produce a dipped beam. There are continuous advances in technology and for all I know such LED sources are available, but if they do exist then anyone out there who knows of such a device would help us all by telling us what it is and where they can be obtained. Sorry if this sounds pompous. :cool:


Well Known and Active Website User
VOC Member
VOC Forum Administrator
I would be interested to know if the only change required to convert a USA headlight back to "normal" is the rim and lens. Were the reflectors also different?
US headlights do not have a separate reflector. I think the shells are different, the rims aren’t interchangeable are they?

Texas John

Well Known and Active Website User
Non-VOC Member
I thought the only difference was the bulbs. They have different filament locations, which causes them to dip left or right.

Comet Rider

Well Known and Active Website User
VOC Member
Hi John
It's all in the lenses as to where the dip goes.
When I first built my Comet I fitted a flat dip(no kick up)

Modern lights use faceted reflectors to achieve the same, which with modern plastics and coatings are much cheaper

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