When selecting the size of mirror for mounting your strobe lights, you should consider both the size and weight of the lights. Generally, it's best to use a mirror that is larger than the light itself so that it can provide adequate support when mounted. Additionally, you want to make sure that the mirror is strong enough to hold up the weight of all your equipment without buckling or cracking. If you have heavier lights, then opt for a thicker and sturdier frame material such as metal or hardwood. Lastly, remember to check with local building codes in regards to any restrictions on wall-mounted mirrors - some areas may require specific types of hardware for safety reasons.