In the POH of the Cessna 310B, two "ultraviolet lights" mounted in the overhead panel and lighting the instrument panel are described. They have starter buttons, to turn them back off the dimming rheostat has to be momentarily set to zero intensity. But it is left unclear what kind of lights they are exactly - are they real UV lamps, or just normal filament / LED lamps producing blue-violet light through the blue-colored lenses ? If they are real UV lamps, wouldn't you risk getting burned from the UV rays ?
The UV lights were used because they made the white instrument and panel markings glow brightly without affecting your night vision. It was one workaround alternative, after radium paint was abandoned, to get a similar effect of lighting only the letters and markings. Nowadays the same effect is achieved with instrument post lights and internal backlighting of control panels shining through letters.
The lamps would be UV-A lamps, typical "blacklight" bulbs, and back in those days would be gas filled low pressure mercury vapour lamps, like fluorescent bulbs.
Like fluorescents, they require a ballast (a capacitor) to provide an electrical jolt to start them up, which is what the starter button is for.
If you have them shining at the instrument panel, you aren't going to get that much UV exposure, but probably after many hours if you had some of the UV shining on your forearms and hands, you might start to get a sunburn. It would depend on what sort of hood or shield is over the light to control where the light shines.
The issues of extended exposure to UV, and no doubt reliability issues with mercury vapour lamps and the fact they don't provide useful illumination beyond making white things glow, is probably why they faded from use over the years.