25 year LEO veteran so I have some ideas from experience.
- A single CR123A battery, lots of large doubles already out there.
- Mechanical switch only no parasitic drain. Batteries must be able to work after a couple of years in the light without fail.
- Tough as nails and potted to handle recoil over and over. Revolvers have sharper recoil impulse over semi-auto’s, must handle both.
- 300-500 lumens, needs good spill for peripheral viewing of area.
- Very waterproof, good hinge and sealed.
- Quick attach, tight if a coin screw is used or very low profile if a throw lever.
- 5000k light color, higher gets more glare, less gives lower output.
- Gold plated contact areas. Anodized housing inside and out.
- Removable inserts for UNIV-1, UNIV-2, 1913-1, 1913-2, 1913-3 compatibility.
- Short as possible for use on compact pistols such as Glock-19’s
Battery inserted from a removable light head if o-ringed and still very waterproof possible. CR123A is still the battery of choice as they are extremely reliable. Rechargeable less than 100% reliable batteries turn items from tools to toys and should be avoided.