Slightly different question - does anybody do plug in replacement LED
instrument lights? (would seem a very sensible place to put them, given the
tedium of getting the dash off to replace bulbs)
Yes, like that. Unfortunately not the sort I have, but a good try :-).
Good point. If it was just reducing the voltage, and the LED was a simple
LED/resistor combo (which these probably are), then it would work fine. But
if it worked by introducing resistance, and the current draw of the lamps
had changed, it would all behave a bit differently. However it wouldn't fail
like flourescents do.
We've had this discussion wrt getting 12v out of 24v, remember? A simple
potential divider is sensitive to current drawn. If the dimmer is a
potential divider driving a proper voltage regulator, then the LED thing
will work fine - the led current will be roughly proportional to the voltage
(give or take the approximately fixed voltage drop across the LED). If the
dimmer is a simple resistor in series with the rest of the lamps, it will
behave differently, and if it's a simple potential divider supplying the
lamps, it'll be different again. Of course for the latter two cases, they'd
also be sensitive to bulbs blowing.
In article , Clive
Ah...you're talking about a more complex system than I was envisaging.
I'm seriously out of date with modern car systems.
(P.S. The lack of insult in a reply denotes a serious question, not a
TBH I don't know what arrangements are used for instrument light dimmers -
it could be a simple variable resistor as you suggest in series with all the
lights, with all the flaws which go with that. Changing the current drawn by
the bulbs (ie the resistance) changes the behaviour of the dimmer - half
brightness would move to a different position, and potentially it may not
dim as much as before. Eg the resistor required for a 0.05 to 0.1A current
range on 12V (assuming constant load resistance) is 0-120 ohms. Put in a
20mA LED, which has say a 500 ohm resistor to make it work off 12V (2v volt
drop on the LED), and the existing dimmer resistor now only varies the
current between 20mA and 16mA - ie the dimming is much less.
(Mine feels like it's a bit more sophisticated than that (ie it's not a
wirewound pot) - but I don't know what that means in practice.)
I guessed :-) Apart from a mild pisstake at the beginning, I gave you a
serious answer :-)
In article , Clive
It is on the Capper. On some of the trucks I drive, it's a button you
press and release when the brightness is what you want, suggesting some
more complicated electrickery. Same result but one justifies a higher
wage for the designer.
I'm trying to change, honest.
Tee hee. I can see one advantage - only one digital input, the rest solid
state and thus theoretically less likely to go wrong, mechanical bits being
natural failure modes n'all. It might even be cheaper, especially if the
electronics are built into something which is already there. But on the
whole it does sound a bit like overkill :-)
Both, really. I was actually looking at some which have LEDs on the back
(same as those in the example), and clustered around the sides giving
loads of light to the sides. Probably not still legal...
Asthetically? Yeah good point. I'm not into dodgy light mods etc., but I
was wondering if these things had any value.
In article ,
You can of course dim an LED by increasing the series resistance. The
problem is the value of the pot for the original bulbs is too low for
LEDs. If you change all the panel lamps for LEDs you might be able to find
a suitable value one which will fit, or use the original and add some
electronics to get the correct law.
LEDs as you probably know are very bright and so would help when braking, in
They are also directional. Meaning that the light emited will be pointed
straight out of the bulb and very little out of the sides. On a normal bulb,
light emited from the sides would reflect on the lamp-holder and iluminate
the whole of that segment of the lamp-holder. I dont think that this would
happen with an LED brake light. It would be very bright though.
Also, if the bulb is not pointed straight back, or people werent looking
straight at the bulb then the effect would be lost.