Why LEDs are more efficient than light bulbs

Over the last ten years, LED lights have dominated the market and brought new innovations in the field of lighting. It has slowly begun to replace more than a century of used incandescent light bulbs and fluorescent lamps. Why have LED lights started to gain such massiveness only now, and what is it that makes LEDs more efficient than a incandescent light bulb or a fluorescent lamp?

The low efficiency of the incandescent light bulb is very easy to understand. In a glass flask from which air is extracted, there is usually a thin tungsten fiber which is heated by the passage of an electric current. The fiber needs to be heated to 1730 to 3030 °C. As a result, only 5% of the energy is radiated in the visible spectrum and the rest is converted to infrared radiation and heat.^[1]

The fluorescent lamp works on the principle of a glow discharge of gases under low pressure, most often argon and mercury vapor, which fills a long glass tube. This discharge generates ultraviolet radiation, which is transferred to the visible area by a phosphor on the inner wall of the fluorescent lamp. As a result, the fluorescent lamp heats up significantly less than an incandescent lamp, converting approximately 22% of its energy into visible light. Thanks to the longer life, which is 10 and 20 times longer than the life of the incandescent light bulb, the fluorescence is significantly more economical.^[2]

The principle of operation of the LED is based on a PN junction, i.e. a combination of a P-type semiconductor that has a shortage of free electrons and an N-type semiconductor that has a surplus of free electrons. If the PN junction is connected in the forward direction to a voltage source higher than the diffusion voltage of the PN junction, the free electrons pass from part N to part P. If one of these free electrons fits into a hole in the P semiconductor, it naturally moves to lower energy level. This releases energy in the form of radiation, which depends on the impurity in the semiconductor material, i.e. the impurity affects the color of the resulting radiation. The radiation has a very narrow spectrum and LED light, unlike light bulbs, has minimal losses in the invisible spectrum. Due to this phenomenon, LEDs are approximately 10 times more efficient than a incandescent light bulb and 2 times more efficient than a fluorescent lamp. Furthermore, LEDs have many times longer life than incandescent light bulbs and fluorescent lamps and in the price/performance ratio it has no competition in conventional lighting.^[3]

Although the physical effect of LEDs has been known for more than 100 years, the technological complexity of production and ignorance of the necessary materials caused a shift in mass production until the 1970s and practical use in the field of conventional lighting until the 1990s. Today, LED lighting has conquered the market and, thanks to advances in smart technologies, has brought hitherto unexplored possibilities of use and interesting prospects for the future.^[4]