Sign on the wall at the armoury at Brecon. "Have you switched off your sights?"yet the US military still felt the need to make the changes and it still cost them a new rifle each time they did.
Presumably you mean batteries in the sight?
The original SUSAT had an etched aiming mark with tritium illumination, so 10 year(ish) ‘battery‘ life but it’s still functional without the illumination, just less effective in low light (but still vastly more effective than iron sights)
The UOR ACOG used a combination of fibre optic and tritium light source to illuminate an etched reticle, so same deal as the SUSAT except the illumination in daylight never goes away.
The current Elcan uses batteries to illuminate an etched reticle, so again, your aiming mark doesn’t go away if the battery runs out (plus they last for thousands of hours and are small)
So in all cases;
In daylight, effective range unaffected
In low light, effective range reduced slightly but still far in excess of iron sights in the same conditions.
Except that STANAG 4172 was the new hot thang and all our SLR's were shagged from being ancient?Again... swap the SUSAT for the SUIT on the L1A1 and you're miles and pounds ahead.