Instrument lighting

Thought I'd try a post here just in case someone has an answer.

The instruments on my SD1 are white on black in daylight. Look perfectly normal.

At night, they are an early example of back lighting. The faces are made of clear plastic with the fronts printed in black with white lettering, and green lighting from the back, which makes the numbers light up green. Very effective, and unusual when I first saw it. However, over the years the actual needles have got dimmer and dimmer to the point where they are difficult to read. The numbers aren't affected, so to me that rules out the bulbs, etc. The interior of the unit is spotless.

There is no light source to the front of the face, so any light getting to the needles is spill round the edges of the unit. And perhaps reflected by the casing which is white.

My thought is the needles use some special paint which is ultra reflective or reacts in some way to green light. Which has failed in some way - but still looks normal in daylight.

Reply to
Dave Plowman (News)
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My thoughts are of the 1957 (ish) MG Magnette where the panel lighting was a form of ultraviolet, so the hands and numbers were visible but no light was emitted as scattered light. In the one I rode in the speedometer hand was dimmer than the numbers at night, and in daylight it looked dirtier than the numbers. I wonder if the construction led to a build-up of static in the hand which over time attracts contaminants which dulls the reflectivity of the hand, whereas the numbers were on an earthed metal plate where the numbers form a very small proportion of the total surface.

Does yours show this effect? Alternatively, is there an ultra-violet effect from your green bulb which might be lessened by evaporated filament coating the inside of the bulb envelope?

Have you considered replacing the bulb to see if that restores the original brightness?

Jim

Reply to
Indy Jess John

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