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A nightlight is a small light source, usually electrical, placed for comfort or convenience in indoor dark areas or areas that become dark at certain times.

Contents 1 Use and culture 2 Health issues and controversy 2.1 Cancer risk 2.2 Nearsightedness 2.3 Protection against diabetic retinopathy

People often use nightlights for the sense of security they provide them, and for a solution against nyctophobia (fear of the dark). Besides their usefulness to children in the allaying of their fears, nightlights are also useful to the general public by showing the general layout of a room without turning on a major light, for avoiding tripping over stairs or obstacles, or to mark an emergency exit. Exit signs often use tritium in the form of a traser.

There are a wide variety of nightlights. Most based on incandescent bulbs have a power usage of less than 10 watts; lights based on more efficient technologies, e.g. neon lamps and LEDs, use 1 watt or less. They sometimes have a light-sensitive switch which activates them only when it is dark enough for them to be required. Some others even include an integrated rechargeable battery so that the light will continue to function during power outages.

A 2004 study [1] of childhood leukemia has shown strong evidence that "light at night" (LAN) increases the risk of certain cancers. This may be due to the disruption of the normal production of melatonin, which has shown the ability to protect the body against cancer development.

At least one study [2], at the University of Pennsylvania, indicated that sleeping with the light on or with a nightlight was associated with a greater incidence of nearsightedness in children. A later study [3] at Ohio State University, however, contradicted the earlier conclusion. Both studies were published in the journal Nature.

Another study [4] has indicated that sleeping with the light on may protect the eyes of diabetics from retinopathy, a condition that can lead to blindness. However, the initial study is still inconclusive.