Disappearing needles.

[RJH]

On 15/10/2014 23:56, Johny B Good wrote: snip

How does the paint get its 'charge'? If there's sufficient light from the other dash lamps, the needles would show at least a little.

[Dave Plowman (News)]

The speedo and tach have two 2.2w lamps each. Both with light guides to distribute the lighting evenly round the numerals on the face, which are back lit.

Leaving the other three - 1.2w - lamps to illuminate the oil, fuel and temperature gauges - ie one each. No extra lamps for the needles. No LEDs. No fluorescent tubes as needles either. Just one lamp per instrument shown in the pic.

[Dave Plowman (News)]

Here are some pics of the spare unit in various stages of dismemberment. So we can perhaps get away from the idea a bulb has failed. As there is only one to fail...

[JimK]

/Here are some pics of the spare unit in various stages of dismemberment. So we can perhaps get away from the idea a bulb has failed. As there is only one to fail... /q

Er seems obvious but do the needles on the spare unit glow in the dark?

Jim K

[Dave Plowman (News)]

Remember I've had this car from near new. And they didn't then or now.

[JimK]

/Er seems obvious but do the needles on the spare unit glow in the dark?

Remember I've had this car from near new. And they didn't then or now. /q

Er? so do the spare unit's needles glow in the dark or not?:-)

Jim K

[Johny B Good]

I realised, after posting, that I could made it clearer. What I meant to emphasise was that the phosphorescent paint used on analogue clock dials and watches is _not_ suitable. It needs to be a fluoresent paint where it somehow fluoresces a bright geen (or whatever stand out colour) by excitation from the yellowish tungsten lighting of the 1.2W panel lamps.

Fluorescence usually involves excitation from the shorter wavelength radiation energy typically present in the source illumination (the UV content in daylight, even on a cloudy/overcast day provides sufficient shortwave energy to make high vis safety vests stand out).

Since there's very little UV radiation emitted by ordinary filament lamps and virtually none when the filaments are run at lower temperatures for panel lamp duty, I can't see the usual fluorescent paints being effective in this case so I suspect the use of an anti-Stokes phosphor was what was used in manufacture.

Such phosphors can convert the near infra-red energy (so copious in such under-run ultra long life incandescent lamps) into visible light (typically green and red emission spectra with the red being about 2% efficient, about ten times better than the grreen anti-Stokes phosphor).

[Dave Plowman (News)]

Must be some kind of smart dimmer if it can dim the needles but not the numerals - all lit by the same bulb.

[Dave Plowman (News)]

It's a simple wire wound pot. Which works in the same way it always has.

[Dave W]

I suggest you polish up the white backface of the window that covers the dials, as well as the white bulb compartment. The light from the bulb should be reflected down below the dial, onto this white face, and back onto the needle. Also make sure the bulb filament is sufficiently forward to light the whole compartment. It could be that the bulbs you use now have their filaments lower down in the bulbs than the originals.

[Dave Plowman (News)]

I ask again - how can the dimmer affect one without the other?

I ask again - how can that affect one without the other?

Strange I should want to do something about it after 25 years...

It is beyond your imagination that some form of high reflective paint might loose its reflective qualities over time? But then so much is beyond your imagination.

[Dave Plowman (News)]

Always knew you lacked the power of reason. Thanks for confirming it.

[Dave Plowman (News)]

Quite. I've not yet removed that particular part of the cluster to check. However, I did have the speedo/revcounter one out recently to lubricate the trip counter re-set mechanism, and it was spotless inside. As is the spare. Which suggests they're well sealed.

The bulb is very small with a large 'spiders web' filament which virtually fills it. It's not possible for the bulb to be in the wrong place and still work due to the holder design. It would also mean all four had 'altered' in the same way.

[Peter Parry]

Could you touch up the pointer with fluorescent paint and mount a UV LED in the space in the moulding below each of the instruments themselves? That should make the needle visible without affecting the dial illumination.

[Dave W]

Something else to check is the back surface of the dials which might reflect light into the white enclosure. Also the meters should not be too close to the front window. I should think a certain amount of space is needed for the light to get back onto the needles.

[Mark]

so why not try some reflective paint on the spare unit

-

[JimK]

/me /Er seems obvious but do the needles on the spare unit glow in the dark?

Remember I've had this car from near new. And they didn't then or now. /q

Er? so do the spare unit's needles glow in the dark or not?:-)

Jim K /q

Er?? Any news?

Jim K

[Dave Plowman (News)]

Thought I'd answered that. No they don't.

[Dave Plowman (News)]

Plenty of red herrings, though. ;-)

It's a fairly involved job removing and stripping the unit. Besides, I already have a spare unit here - but can't simply swap it as there are slightly different gauges used across the various models.

Not in this case, since no one there has found a cure. Hence asking here. But mine does seem worse than other member's cars - perhaps because it lives outside and always has done. Also, perhaps the majority are only now taxed for the summer months so may not be used in the dark much.

[Dave Plowman (News)]

Still trying to get out of you what sort of dimmer could leave the backlit numerals perfectly normal but affect the needles only - since they both share the same light source, a single bulb.

It might help explain the twisted 'logic' you display with so much else.