I always thought the needles in today’s dahsboards are lighted by something similar to total internal relection (how fiber optics works). But, my dashboard doesn’t light properly, and the needles partially illuminate - dark from the midpoint to the tip. So, this makes me wonder just how are the needles lit? Very teeny tiny bulbs? Maybe it should be obvious, but it eludes me.
I always thought that they were light pipes (like low tech fiber optics) but I suppose they could also be illuminated with tritium, like a Luminox watch.
Generally, there are small bulbs behind the dashboard display, one per pointer, and the light shines up the shaft and illuminates the pointer. Modern cars may have something more sophisticated.
Here’s a picture of the back-side of the dashboard illumination circuit board.
ETA:
Oh, and if all your pointers are dark, that circuit is probably bad, and they are only getting light from the general dashboard illumination.
I used to have a 1987 Porsche 944 that I purchases new. About six years into ownership my dash was so dim you couldn’t see the dials at night. Come to find out Porsche choose to get the soft backlighting by using 3 bulbs behind the dash and a reflective surface under the dials. This reflected the light in such a way that it produced a very pleasing glow. I also found out that the reflective material was notorious for breaking down at the 5-7 year mark. The only way to fix the problem was to purchase a brand new instrument cluster, from Porsche. Lets just sat the replacement cost was expensive, over a grand if I remember right - ouch.