It is the abbreviation or acronym of “Light Emitting Diode”, a semiconductor device made of a “wafer”-like structure with a P-N junction emitting a single-colour light when direct current (Vf) polarises it and an electric current (If) passes through it.
As a semiconductor, it is composed of silicon, a grain of sand emitting light when duly “doped”and sent through by current.
Although the first findings about electroluminescence emerged from the studies of the English scientist Henry Round around 1907, evidence of the first LED component dates back to 1962, when Nick Holonyak, a physicist working for General Electric, presented the American Institute of Physics an element composed of Gallium arsenide (GaAsP) whose emission is visible in the red spectrum. Holonyak’s invention paved the way for the construction of the first component for light signalling devices and then the earliest screens of watches and pocket calculators in the Seventies.
Since the Seventies, LED applications have increasingly developed thanks to innovating materials and the continuous evolution of semiconductor production technology. Such studies led to a higher light emission, improved efficiency and a wider range of colours by means of new phosfor lining and compounds deriving mainly from substances like Indium and Gallium.
The introduction of LED technology in the Lighting sector brought about numerous advantages to consumers. If light means emotions, LED supplies a more effective, efficient and dynamic light. Other major advantages include a rather longer service life compared to the traditional light sources, high reliability and reduced energy consumption. The above mentioned aspects all lead to“Energy saving” -minimum need for maintenance and effective light control, that is to say operating savings and protection of the environment.
Yes, we can! LED can be considered as an eco-friendly technology as it is mercury-free, unlike HID and fluorescence bulbs. The new Directives for the design and construction of lighting equipment expressely prohibit the use of hazardous substances while providing for characteristics such as environmental friendliness, reduced energy consumption and longer lifecycle. Directives such as RoHS 2.0 (Directive 2011/65/CE for the restriction of use of certain hazardous substances), WEEE (Directive 2012/19/CE about electric and electronic waste disposal), ecoDesign (Directive EUP 2005/32/CE and Directive ERP 2009/125/CE) and Energy Labelling 2010/30/CE regulate the placement of products on the market and protect consumers and environment from the potential risks of low cost products and/or imported products not entirely responding to the Laws/Regulations or engineering and good technique standards issued by standardisation bodies.
Absolutely. For instance, LED devices are switched on and off with no delay, thereby eliminating any annoying initial flashing; in addition, the number of on-off cycles does not deteriorate LED lamps, which is not the case for fluorescent lamps.
Weakness is not the right word here. Actually, it’s about a good sense of manufacturers who take special measures for consumers to enjoy all benefits offered by LED technology. In a nutshell: LED devices generate heat just as all electric components using current, although less than the others. In order to make an LED live long, it is advisable to equip emitters with wide surfaces able to dissipate such heat. The lower LED junction temperature, the longer its service life. By doubling LED junction temperature from 75°C to 150°C, service life is more than 70% shorter. For instance, keeping LED at 90°C means 90,000 hour life, while at 110°C , service life drops to about 65,000 hours. Besides, the higher the temperature with the level of current and voltage unchanged, the lower the light emitted. Other factors to consider when choosing “trouble free” products include the kind of power supply unit or driver, which should be manufactured according to long life criteria (5 year warranty) and key electrical characteristics, such as > 0.9 power factor (cosfi) and protections against overvoltage, overcurrents and overtemperature.
As regards electric safety, lamps must comply with LVD Directive (2006/95/CE), while electromagnetic compatibility issues fall within EMC Directive (2004/108/CE). Only the products which are 100% compliant with Community Directives and European standards (EN standards) can be marked CE and marketed in the European Economic Area (EEA). Thus, manufacturers must certify their compliance with Directives and applicable standards by undersigning a certificate of conformity making reference to the design criteria, components used, and tests performed collected in the Technical File and made available to the Supervisory Authority.
Light quality and colour stability are ensured by accurate LED selection processes. It is essential to guarantee even colours from different LED lighting devices and characteristics remaining unchanged over the years according to the different environmental conditions. As LED cannot reproduce exactly the same colour temperature, light quality depends on how accurate manufacturers are when matching components. Such process is called “binning” and considers any deviation from Mc Adams ellipses. The wider the allowed deviation, the lower the quality of light. As no difference is perceived in colour up to three deviation steps, high quality products are equipped with LED complying with such restricted tolerance range.