Shabbat lamp
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A Shabbat lamp is a special lamp that has movable parts to expose or block out its light so it can be turned "on" or "off" while its power physically remains on. This enables the lamp to be used by Shabbat observant Jews to make a room dark or light during Shabbat without actually switching the electrical power on or off, an act that is prohibited during Shabbat.
[edit] Halakha of the Shabbat lamp
There are various Jewish laws governing Shabbat lamps that allow them to be used during Shabbat.
The lamp itself is muktzah during Shabbat, and therefore, it cannot be moved from its location where it is placed. However, the component that is use to open or close the light is not attached, and under Jewish law, has the status of a lamp shade, which can be moved during Shabbat in order to control the amount of light that is exposed[1].
Shabbat lamps are lit by and only accept a compact fluorescent lamp. These bulbs do not contain electrical filaments like those found in incandescent light bulbs, and therefore, according to some rabbinical authorities, do not constitute a fire, but rather, an electrical appliance that is permissible to move in order to change the location in which it is being used or to free up its space, provided that it is not accidentally unplugged. Regardless, during a Yom Tov that does not coincide with Shabbat, the lamp may be moved if it is not unplugged, as moving a candle on such a day is permitted[2]
The compact fluorescent lamp that must be used also has the benefit of using a minimal amount of energy, as the lamp must remain on for a period of at least 25 hours.
