- I take 10 shots. 3 of these will come out slightly darker than the others - why is this?
If it's florescent lighting, you're probably using too fast of a shutter speed. The lighting is actually turning on and off at 120 times per second (if you have 60Hz power or 100 times for 50Hz, locale dependent), so fast shutter speeds may be capturing between cycles. Try slowing your shutter speed down to 1/30th and see if that helps.
LED lighting
may flicker, depends on the quality of the bulb. Good quality LED bulbs convert to filtered DC, and provide continuous light. Medium quality bulbs use a full wave bridge rectifier and will flash at 120Hz(100Hz). Low quality bulbs (commonly Christmas lights), use a half wave rectifier, and the pulses of light have the same duration as the "medium" quality one, but every other one is missing so it's flashing at 60Hz(50Hz), but is off half the time.