Osram lamp, blue, in box. Marked with 'the property of the war department'.

Part of the Bob Gray collection of electrical objects.

This incandescent electric lamp with heavy blue shielding was produced for use during black-out conditions, 1939 - 1945. Blue light penetrates less far into the atmosphere than red and yellow light. These bulbs were therefore used where street lights were banned and inside lighting was not allowed to be visible from the outside. The lamp is marked as property of the war department so was likely produced as part of a contract for military use. The small clear circle at the bottom of the lamp is designed to allow a small amount of clear light to radiate downwards.