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Basics of LED technology

White LED's

The entry of LED technology in all areas of lighting technology is advancing inexorably and with remarkable speed..


A new product will be accepted only from a customer when it granted him an advantage over an existing product.
This is exactly what happens in the case of LED lighting:
The maintenance costs of the lighting will be reduced by up to 60%.

With a lifespan of over 60,000 hours omitted maintenance by replacing the bulbs. It drop at the disposal of lamps, at the end of the service life, no heavy metals such as mercury or similar to. So it is not surprising that this technique has introduced a fundamental change in lighting.

Construction of a LED

The LED (Light Emitting Diode) is a semiconductor device that can pass current in only one direction.
When current flows in the forward direction, so the LED, depending on the semiconductor material and the doping (introducing foreign atoms), light radiation emits.

Basic structure of a light emitting diode
aufbau led

How is white light generated?

The conventional method for white light to be generated is, that the light from a blue LED and a wide-band luminescent dye is merged

erzeugen weißes licht

Mounting types of LED

There are two basic types of mounting for white LED:

Surface mount components (SMD)
    Die LED wird direkt auf die Leiterplatte gelötet. Im Gegensatz zur The LED is soldered directly to the PCB. Unlike the operation with "wired components" requires the SMD technology requires less space and enable better thermal connection
Surface-mount LED chips (COB)
    The unpackaged (naked) semiconductors are applied directly to the substrate (base material). This method allows a multiple of "density", compared to the SMD technology, achieve. The enormous lighting advantage of COB modules lies in the homogeneity of the light emission. Thus, a consistent light cone and no individual is achieved light points. Will also used as support material Ceramics, the prerequisite for optimum cooling is provided, which helps to increase the efficiency and lifetime.

aufbau smd modul aufbau cob modul

SMD Modul

COB module, clear contours by homogeneous
light emission with COB technology

bild aufbau cob modul

Schematic structure of a COB module

Quality characteristics of LED's

The quality of an LED module is i.a. determined by the failure rate and the decline in luminous flux over the lifetime.

Failure rate
    Under the failure rate of LED modules one understands the percentage of LED modules that emit no more light. The usual failure rate for LED modules is 0.2% per 1,000 hours. That means after 50,000 hours, up to 10% of the modules have failed. The failure rate is indicated by CZ.
Decline in luminous flux (degradation))
    Over the lifetime lose the LED modules, due to chemical and physical changes in illuminating power. The degradation over the lifespan is described with the variable LX. The varable LX indicates which luminous flux according to Rated lamp lifetime of the LED modules will be reached. For example, L70 with 50.000 h means, that after 50,000 hours still 70% of the initial luminous flux can be achieved.

    In addition to the failure rate CZ also the error portion BY is directly related to the Rated lamp lifetime LX. The varable BY specifies the percentage of LED modules, which may fall below the value LX. A common specification is B50. This states that 50% of the modules, for example, after 50,000 hrs., below the value of L70.

    The life span of LED modules is specified so taking into account the gradual (z. B. L70 / B50) and the suddenly lumen depreciation (z. B. L0 / C10). Thus, the effects of aging and the total failure of an LED module to be considered
Luminous flux
    The luminous flux (lm) depends on the amount of current in the operating device (driver). Major driving currents are 350/500/700/1050 mA. The higher the driving current, the larger the light output. Similarly the luminous flux is dependent on the color of light. As "colder" the light (high color temperature) as greater the flow of light.


With efficiency, the ratio of luminous flux L in lumen (lm) to used electric power P in watts (W) is designated. It should be noted that when the power system performance (illuminant plus Control unit) and in the luminous flux, the "warm Lumen" (luminous flux at operating temperature) be used.
An optimized system solution provide thereby coordinated components. Characteristics of the individual components help to make the right choice. The characteristics of the LED drivers are primarily the efficiency factor and the power factor. In this case, the efficiency of> 0.85, and the power factor for equipment should be with a connected load> 25 W at 0.9.

Light color

This setting is laid down in the "Photo metric Code" and applies to LEDs in the same extent as for fluorescent lamps. Example: 830 is
    8 = color rendering index (CRI)> 80,
    30 = 3000K. If the use of "cold" light color is possible, the efficiency of a lighting system can be further increased.
Information in Kelvin (color temperature), for example.
    3000 K for warm white
    4000 K für Neutral white
    5000 K für Cool white

Color rendering

For calculating the color rendering index CRI have been defined 14 test colors. For calculating the generally color rendering index Ra, however, only the first eight test colors be used.


Colour Rendering Index, CRI > 80

This value represents an average, at the same CRI deviations in the individual colors Ri can be present. Depending on the visual task (Color detection in textiles, office work, working in a control room) are the requirements for color rendering greatly.different
If no specific conditions placed on the color reproduction, which can be used to the benefit of efficiency because, with decreasing CRI value increases the light yield.

color tolerance

MacAdam ellipses are used to determine visual color deviations.
They represent the surfaces in the color chart, in which the comparison colors to a reference color around, be perceived at an equal distance (MacAdam:. American physicist). Up to 3 MacAdam color tolerances are virtually undetectable. For major deviations between color differences are visible, even with the lapse of lifetime may increase.
It can be clearly seen that the MacAdam ellipses in green and yellow region of the CIE color space are significantly larger than in the blue or violet range. This effect demonstrates that the human eye color differences in the green LEDs less than noticed in blue LEDs.

McAdam Elipsen


Production caused deviations of the luminous flux and the color temperature can be caused by tolerances in the smallest LEDs.
To keep these differences to be minimal, the LEDs are divided into tolerance classes (Binning). Thus, the quality is directly dependent on the tolerance limits.

Thermal management

Both the light output as well as the lifetime of a LEDModuls critically dependent on the thermal management.
The heat is dissipated via board and lamp housing (= passive cooling). A large-scale, fixed connection of the printed circuit board and housing aids in heat dissipation.
Some luminaire models larger cooling fins, the surfaceand so reduce the temperature at which other types of construction also air or water for active cooling are used.
Heat dissipation is an important quality characteristic of LED lighting, because without cooling, the life would be reduced to a few hundred hours.

Light Control

Basically, LEDs can be dimmed. As popular technology, the pulse-width modulation (PWM) has been established.
Interfaces for the known Light Control signals 1-10V, DALI, DMX for conversion into a PWM signal to buy or integrated devices are offered.

Pulsweiten modulation

Standards and Guidelines

    LED modules for general lighting
    DIN EN 62031 (VDE 0715-5)
    Here are the requirements for safety and compliance conditions and test methods for LED modules, with and without integral control gear, established.
LED control gear
    IEC 61347-1 und IEC 61347-2-13
    Here the requirements have been defined for the safety of operating devices for LED modules.
Standardized language arrangements for LED technology
    IEC 62504 (CDC stage)
    Here uniform terms and definitions are given, which are to ensure that the LED technology can be carried out similar assessment on the basis a common understanding.
    IEC/PAS 62717 (LED-Module) and IEC 62384 (LED control gears)
Photometric specifications have been drawn up in the technical committees of the CIE:
    - Standards for LED intensity measurements TC2-46 CIE/ISO
    - Measuring the optical properties of LED clusters and arrays TC2-50
    - Measurement of radiation and light density of LEDs TC2-58
    - Optical measurement of high-power LEDs TC2-63
    - Quick test method for LEDs TC2-64

The photobiological safety of lamps and lamp systems:
    IEC 62471, DIN EN 62471 (VDE 0837-471)
    This international standard, which is conducted in Europe under the Low Voltage Directive for Security, describes how to as light sources, including LEDs, LED modules and LED lights, measured and evaluated.

    Considering the continued rapid advances in LED technology should Zhaga, an international consortium of the lighting industry, interchangeability of allow products from different manufacturers.
    Interchangeability is achieved by defining interfaces for a variety of application-specific light engines (combination LED modules and control gears).
    Zhaga specifications cover the physical dimensions, as well as the photometric, electrical and thermal parameters of LED Light Engines (LLE).