The door handles are self-illuminating. They do not require an external power supply, e.g. batteries or bulbs. The Betalux will remain continuously illuminated, even during prolonged periods of darkness. Illumination is powered by Betalights, gaseous tritium light sources that provide an absolutely reliable luminance throughout their practical life of 15 years. They contain no loose parts or unsustainable components (such as batteries, bulbs or switches). Betalux door handles are suitable for use in hazardous atmospheres and will operate normally in adverse environmental conditions, even when immersed in water. They are calibrated for operation in temperatures of -60C to 80C.