I built a similar light back in 1983 using a low-power red LED, a Kodak film canister, switch, resistor and two N-cell batteries. I used it for close-up map reading and other stealthy navigation while preserving my night vision. I still have it but clipped the batteries out long ago. I was going to put in actual holders rather than endanger myself soldering to the batteries again. Would probably also replace the LED for a little more output.
One neat aspect was my "no-roll" solution for a round object. The batteries were off-center. It would rock but not roll.
I'm sure it would get me in severe trouble these days. It looked alot like a remote trigger from an action movie!