LED has revolutionised the lighting landscape; high light flows ensure superb efficiency and economy, with a life span of tens of thousands of hours. From what was previously the domain of decorative accent lighting, LED technology has evolved into a practical, general lighting option. Fagerhult are developing luminaires specifically for LEDs, creating viable solutions across the whole spectrum of a lighting project. Drawing on over half a century of lighting know-how and innovation, this approach has focused on softening the intensity of the light to create a harmony between efficiency and comfort.
How LED works
A semi-conductor that emits light
An acronym for Light Emitting Diode, an LED is a semiconductor that radiates light when subjected to electrical impulses. It runs on direct current (DC) and often requires a separate electrical ballast. LEDs are very small; the active light-emitting surface is no bigger than 1–2 mm². A single diode can rarely produce enough light for a given lighting situation. For the unit to work, it must be mounted on a circuit board, with multiple LEDs combing in a cluster to form a LED module.
The colour of the light depends on the materials the LED is made of. The main colours are red, orange and green, and a variety of shades of blue. The most common way to create a white light is to apply a phosphor-based coating to a blue diode. The phosphor converts the blue light to white light in a range of colour temperatures. The quality of the white light is affected both by the choice of LED and by the properties of the phosphor.
Comparison of light sources
Comparison Lamp
TThe way LEDs emit light when stimulated with electricity differs from traditional light sources, in which the light is a by-product of the filament being heated or of a gas discharge. Because LEDs do not emit ultraviolet (UV) or infrared (IR) radiation, the technology is extra well-suited for lighting in sensitive environments.
In contrast to traditional light sources, LEDs achieve full brightness immediately when switched on and, in fact, the life span of the diode is increased by frequent switching on and off. Equally the light flow increases at lower ambient temperatures, so luminaires with LED technology are the ideal choice for cold rooms and outdoors. LEDs do not contain any moving or fragile parts. Therefore, a properly designed LED luminaire is well-equipped to handle vibrations and other mechanical stress.
Ballast
The importance of the correct driver
LEDs can be powered in two ways: with constant current or constant voltage. The ballast is the heart that drives an LED. Different luminaires uses different ballasts and if the ballast is unsuitable, or improperly connected, it can damage or even ruin the LED luminaires connected to it. Although some LEDs can run on conventional transformers, although these can lack certain kinds of safety features, such as short-circuit protection, which can lead to injuries.
The Future
Looking at the future
Advances in the LED field are astounding. Efficiency has doubled in just a few years, while costs have dropped dramatically. This development is likely to continue, even if the rate may slow. It is not unreasonable to expect that LED systems that produce 100 lm/W today may be up over 150 lm/W in a year or two.
The average annual increase in efficiency is estimated at about 10% by 2015. As volumes increase, costs will fall - but how much more uncertain. A joint standardisation effort called Zhaga is under way in the lighting industry. The aim is to facilitate the replacement of LED components (LED module and ballast), greatly simplifying maintenance while providing the option to upgrade to the latest technology. The first standardised modules are expected to be ready in 2011.
