LED
Elements of LED technology
Generation of light
In an LED lamp (light-emitting diode) there are, besides negative electrons (-), the positive charges (+). These opposing charges generate, upon their neutralisation, visible light and heat. The LED energy balance is approximately 20% light and 80% heat, i.e. there is hardly any heat radiation in the form of IR light.
The heat produced must, however, be discharged from the semi-conductor material elsewhere, by means of active or passive cooling.
That LED technology does
not involve any thermal load for the luminaire system is, therefore, not correct.
Colour temperature of light
There are two LED type classes: one for ‘warm’ and one for ‘cold’ LED colour temperatures
How is white light produced?
There are two practices applied for generating white light from coloured LEDs.
With the first variant, the light of a blue LED is converted into white light with the help of a conversion layer (mostly phosphorus). The second possibility is the RGB principle and in this case red, green and blue LEDs are mixed to produce white light.
Binning
The method for the formation of colour classes and light flux classes in LED production is called ‘binning’.
A ‘bin’ comprises several LEDs of approximately identical light colour temperature and/or identical light fluxes. Quality-orientated producers design their bins on a very narrow-mesh basis in order to keep the variance of colour temperatures within one bin as low as possible. Binning is a time-consuming and costly process – quality has its price.
Dimmability
LED equipment can be dimmed easily and its colour temperatures (in the case of RGB LEDs) are infinitely adjustable. With this characteristic they provide new approaches for dynamic lighting concepts.
In addition, the full luminous flux of the LED is immediately available upon switching-on, while a discharge lamp only reaches 100% of the output with increasing heating.
Temperatur chacteristic and product life
The light flux of an LED rises almost linearly with the power consumption. Unlike an HIT lamp which, with increasing heating up also emits more light, the light flux of the LED drops off with increasing heating up, as does the product life.
The mean product life of the LED chip, often stated as being 100,000 hrs, plays only a subordinate role in lighting practice. What is important here is the definition of the drop in the light flux over the service life of an LED. This results in real effective product lives of 35,000 – 50,000 hours. In order to achieve this target value, good heat management is an absolutely essential prerequisite.
Brilliance
To produce brilliance, point-shaped light sources are required. With an overcast sky and fog high illuminance can in fact be measured, but overall a diffuse light distribution suppresses any brilliance.
Conventional lamps using halogen/and HID technology have a narrowly defined light centre and are particularly suited to producing brilliants cones of light via exact reflectors.
LED units of higher lumen packages have, in comparison with these point-shaped light sources, as a rule, larger effective reflex surfaces. Seen from this point of view, reflector development also needs to be adjusted to this form of light generation.