Redstone Lamp

"Redstone lamps came to Minecraft in 2012 in update 1.2.1 - which also added iron golems, ocelots, chiseled stone bricks and jungle biomes. They give off a light level of 15 - the same as fire and glowstone - but only when powered by redstone. In fact, that’s how they’re made - by surrounding a glowstone block with four lumps of redstone dust in a crafting table."

- Duncan Geere

A redstone lamp is a block which produces light when activated with a redstone trigger.

Obtaining
A redstone lamp can be mined by hand or with any tool, dropping itself as an item.

Usage
A redstone lamp can be used to produce switchable light.

Redstone lamps are redstone mechanisms and can be activated by:
 * An adjacent active power component, including above or below: for example, a redstone torch (except that a redstone torch will not activate a redstone lamp it is attached to), a block of redstone, a daylight sensor, etc.
 * An adjacent powered block (for example, an opaque block with an active redstone torch under it), including above or below
 * A powered redstone comparator or redstone repeater facing the redstone lamp
 * Adjacent powered redstone dust configured to point at the redstone lamp (or on top of it) or directionless; a redstone lamp is not activated by adjacent powered redstone dust that is configured to point away from it.

A redstone lamp activates instantly, but takes 2 redstone ticks to turn off (4 game ticks, or 0.2 seconds barring lag).

An active redstone lamp produces block light 15. An inactive redstone lamp produces no light.

Although a redstone lamp acts like an opaque block in most ways (torches and levers can be attached to it, redstone dust can be placed on it, etc.), an active redstone lamp is "transparent" to sky light, reducing the sky light level by 1.

Trivia

 * Multiple tiled redstone lamps produce a pattern which closely resembles the truncated square tiling t{4,4}.