A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction. The physical effect of electroluminescence was discovered by Henry Joseph Round I 1907. But as he was working on a new radio direction finding method for marine vessels this discovery was initially forgotten. Today white LED reaches efficacies up to 40-100 lm/W (efficiency depends on colour temperature and colour rendering) and is used in a vast number of areas, dive lights being one of them. LED offers a whole array of advantages such as low energy consumption, extremely long life, very low early failure rate, smallest dimensions, shock and vibration resistant, low wattage and high colour saturation.