Have you checked your bulbs to see if they are dirty or covered with dust, I had to remove mine and clean them and it made it brighter.
it might be called "Back Light". It looks kinda cool at night. No glare from it either.....Mark
Removing the "black lite lenses" from the cluster is the only way to get to see your speedo and gauges really good. Some remove all lenses and paint the bulbs green or you could only remove a couple to get at least some light to the cluster like I did.
Have found at bulbtown.com a 6251 bulb like the 55 that is 5 watts to replace the 55 which is 3 watt when they arrive I will see how well they work. No reostat on 49 and 50.
there is a reostat on my 50. had a spare light switch and found the reostst was open in the windings and the one in the car was so bad it was useless, thats why i bypassed it.
Before I retired, the motor coaches that I drove and maintained had covers on all the instrument and warning lights of different colors and thats where I got them.