I think the image must have been too large but it probably would not help anyway. There are two gauges in one housing. The illuminated portion of each face is 1 3/4 X 1 1/1/4 inches. The stepper motor is 1 1/8" diameter. Without extending the shaft, there's less than 1/4" (5-7 mm) between the motor and face. A COB panel will nicely fit in the space between motor and face and that's the reason I posted this thread.
Because the gauge is back lit, much of the light is attenuated by the gauge face. Multiple LEDs are needed but their light is spotty and they are too tall to fit in the space. I've experimented with several LED types. The COB strips that are sold as running lights work great except they must be cut to fit. When placed side by side to illuminate the full face, light is not evenly spread because of the void between strips. Since the strips work fine after being cut I am pretty sure that a small (1/16" or less) hole will not damage the COB. For example, the common conductive strip between individual rows of LEDs is almost 3/16" wide so the hole for the motor shaft could be through this strip.
Couldn't the brightness be adjusted with a simple rheostat or potentiometer?
So what about heat? There is always talk about the heat that LEDs and COBs generate and how the COBs have a conductive base to dissipate heat. The COB strips I have get warm (in open air) but they feel cooler than a single instrument bulb when touched. If sealed into an instrument housing with some ventilation holes, will a COB get too hot? If so, what can be done to cool them?