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How to choose an LED for lighting
Source:    Addtime:5/29/2009 2:56:00 PM

How to choose an LED for lighting


         With developments made in the efficacy of white LEDs in the past few years, LED technology is driving the future of lighting.

As white light is the main driver for general illumination, there is a particularly strong focus on improving the efficiency of white LEDs, which currently outperform tungsten halogen lamps with efficacies from 45-55lm.

Manufacturing methods have allowed for significant progress to be made in increasing the efficiency of LEDs. Previously, the only way to produce white LED light was by the additive colour mixing of the three basic colours using so-called ¡°multi-LED¡±, ie, three semiconductor chips (red, green and blue LEDs) had to be combined.

Today it is possible to produce white LED light with a single chip.

In luminescence conversion, only a blue LED is used, whose light stimulates a luminescent substance that emits yellow light. With interaction, the system produces the colour white.

White light is generated on the basis of a principle similar to that used in luminescent substance lighting. Depending on the composition of the luminescent substance, various white tones can be realised.

Fine binning for homogeneity

Generally in LED lighting applications more light points are visible next to each other than in applications that employ fluorescent or halogen lamps. The sensitivity in terms of light homogeneity is even bigger as differences between LEDs can be easily identified by the naked eye.

In lighting a corridor, for example, white LEDs might be spaced inches apart to illuminate the walkway and differences in the white light being produced would be very apparent if the LEDs were not from the same sorting grade.

It is now possible to use white LED modules that offer refined quality of white light for applications that demand the highest white colour homogeneity.

The supplier can define the colour coordinates for different sorting grades (binning) within very narrow tolerances. Precisely defined colour coordinates ensure that different LEDs within one white group reliably emit the same homogenous white light, with no visible colour deviations.

LEDs from one particular bin can be used in lighting applications without the need for further checks. Even in critical applications such as diffused or tightly packed light sources they meet stringent requirements in terms of homogeneity. The white tone of an LED is within a range that typically corresponds to a three-step McAdams ellipse.

General illumination

As white LEDs with efficacies from 45-55lm/W already outperform tungsten halogen lamps, general illumination using LED technology is becoming a reality.

In terms of professional lighting, LED luminaires are taking lighting design into a new dimension. With the progress made in white LED technology, the most advanced LEDs are now installed in luminaires that are being developed for general illumination purposes.

A few years ago, LED luminaires were not available as replacement products for halogen lamps used for general illumination, but white LED technology has developed rapidly.

It is now possible to produce a high-power LED with a luminous flux of up to 27lm (100mA/5700k). Not only is it on average 15% brighter than the standard version, it is available in different white tones from 2,700k to 6,500k . This means that different white light colours from warm white to cold white can be achieved and all the requirements from linear lighting applications to strip lighting and surface illumination can be met.

Due to an EU directive calling for the phasing out of products that waste a high amount of energy, conventional tungsten filament lamps will disappear from retail shelves over the next few years and trends within lighting design will have to adapt.

LED technology is already demonstrating itself as a versatile and efficient choice for decorative lighting effects and the scope for using white LEDs for general illumination is enormous through the technological developments that have taken place in recent years.

LEDs are changing the future of lighting and it is estimated that by 2020 LEDs will represent at least one third of the general lighting market.