A popular peripheral, originally bundled with the "Master System Plus" pack with Safari Hunt, but also available as a separate peripheral. It is far superior to the NES Zapper, having a better trigger action and futuristic styling. It is also suprisingly accurate too! It plugs into the joystick port of the PowerBase, and is compatable with both models.
The Light Phaser will only work with games designed specifically for it.
When the trigger is pulled, the screen flashes briefly for a split second. What the Master System does is blank the screen to black, except for the sprite you are shooting at, which will become white. The Phaser looks for the reflection of the white sprite; If it senses the reflection of the sprite then it will register as a hit, if not it will be a miss. The Phaser will often work better with the contrast of your TV / monitor turned up slightly to make the white "target" brighter.
I have a spare Light Phaser if anyone is after one.