How a powder magazine was lit without an open flame

How did sailors illuminate a powder magazine without bringing a flame near the powder?

The lamp or candle sat outside the magazine in a separate enclosure and shone through a glass window.

Rather than carrying even a small flame into the powder room, the ship placed the light on the far side of a glass window. The lamp occupied its own compartment outside the magazine, keeping heat and sparks physically separated from the powder. The arrangement shows how seriously sailing navies treated explosive safety.