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LEDs - an efficient all-rounder

23-10-2014


LEDs: An efficient all-rounder

From domestic households and the catering sector to industrial applications – light emitting diodes (LED) are becoming ever more popular, because high quality LEDs in particular from renowned manufacturers such as the lighting expert Osram feature significant benefits compared to standard light sources. They feature good colour rendering, high energy efficiency and durability, consequently reducing running costs such as power overheads or replacement costs.

The structure and principal of LEDs

Light emitting diodes consist of several layers of semiconductor material that generate light upon the application of DC voltage. In contrast to incandescent lamps an LED is a monochromatic light source, and according to its composition emits light with a specific colour. White-emitting LEDs also initially generate monochromatic light that must then be converted, and this is usually achieved with a combination of blue LEDs with a yellowish phosphor layer or by mixing the light of red, green and blue LEDs (RGB). Furthermore, specific RGB colours can be mixed to create an infinite number of colour tones by varying the mixing ratios.

PET PCBs for greater flexibility

Typical LED modules consist of several combined LEDs, a fixed PCB and various other components. A practical alternative to fixed fibreglass PCBs are flexible materials based on polymers, as these enable the production of LED modules with a high diversity of forms, in turn opening the way to new designs and lighting solutions. Flexible light engines can also be manufactured on rolls, providing simpler handling as well as automatic manufacturing and the reduction of stock keeping overheads.

A robust, non-conductive material with a high optical reflection factor is ideal for producing such flexible PCBs, and the material should also be environmentally compatible and chemically stable. Such requirements are best fulfilled with polyethylene terephthalate (PET) versions. With regard to these advantages, the lighting manufacturer Osram developed its PrevaLED Flex Linear light engine that fully exploits the benefits of flexible PET PCBs. The light engine consists of a thin and pliable copper layer in which the requisite circuit has been etched and sealed between two PET layers.

An efficient direct current solution

Due to the electrical properties of LEDs, their drivers should directly supply a constant current to the module. The reason for this is that in contrast to LED systems requiring constant voltage, other current control components on the module are not needed with systems supplied by constant current directly from the LED driver. This provides efficiency increases of 5 to 15 per cent. A sophisticated system for grouping and mixing the various LEDs (various bins) is used to achieve homogeneous voltage distribution in the LED lines various (also switched in parallel) with simultaneous constant current operation, thereby also avoiding brightness and colour deviations within the partly long and flexible systems. This in turn enables a uniform distribution of light colour and brightness, across each section and the complete module.

Light on a strip

In addition to flexibility, a special benefit of the strip solution is cutting the strip to suit according to the desired length, enabled by switching the LEDs in parallel. With the Osram PrevaLED for example, the strip can be cut after each segment without the module forfeiting any quality of light. One segment has a length of either 93.3 mm equipped with 10 LEDs or 140 mm with 12 LEDs, and the length itself is restricted merely by the supply of current, which must be as homogeneous as possible for all LEDs to create light with high uniformity. In this regard the distance between the current source and the LED is an important factor – the maximal length of a flexible LED module with single-sided power input is currently 1.5 metres, and module lengths of three metres can be achieved with central power input. As a consequence, the length of the light strip can be individually modified between approximately 10 cm and three metres, and installations that previously required the back-to-back switching of several modules can now be produced as one unit.

PrevaLED also cuts installation costs by up to 30% compared to standard lighting solutions. The LED strip can be bonded simply into luminaires or luminous elements, enabling the saving of valuable work time. The broad flexibility of PrevaLED comes to the fore during simple installation and the implementation of sophisticated design projects, and the PET strip can for example be bent to form a circle with a radius of just 15 cm. With a colour temperature of 4000 Kelvin, a good colour rendering index of over 80 and up to 170 lumens per watt, PrevaLED Flex is not only a genuine alternative to fluorescent tubes but also opens up new possibilities for designing light.

strip
PrevaLED Flex module. The flexible LED strip can be cut-to-suit after each
segment to achieve precisely the required length.


 

flexible
New designs can be simply implemented with flexible PrevaLED Flex modules.

Light with savings potential

With regard to power consumption, the emission of greenhouse gases and maintenance costs, LEDs from quality suppliers such as Osram offer high potential for savings without any sacrifices in terms of light quality. If the significantly longer lifespans are also considered, the total calculation is distinctly positive. When upgrading to LEDs, power costs according to the specific system solution can be cut by up to 80%. Incandescent lamps in this regard are characterised by an efficiency of around 10 lm/W, halogen lamps have approximately 20 lm/W and fluorescent sources have 70 to 90 lm/W. Comparable white LEDs achieve an efficiency of between 70 and 100 lumens per watt according to type and light colour, with LED power consumption (according to type) being merely 0.1 to 15 watts. This means that even highly compact LEDs provide powerful lighting.

It's a question of quality

In order to exploit the complete spectrum of advantages inherent in LED technology, when selecting the appropriate light source this mainly concerns the quality of components. The light source manufacturer Osram has upgraded its portfolio, helping consumers to more simply identify high quality LEDs at a glance, and will present its largest LED lamp spectrum until now in the autumn of 2014. More than 90 LED lamp types will be available in the retail market with easy to recognise, uniform designs, and the consistent look of the popular candle, drop-shaped and mainly pear-shaped classic LED lamps will be characterised primarily by their smooth, white heat sinks. The uniform designs of the Osram lamps go beyond similar appearances to also provide a highly practical aspect – all lamps are based on identical modules used in different lamps.

Retrofit lamps are especially suitable for refurbishing classic lighting systems to energy- efficient and durable LED technology. An example are lamps from the Osram Classic A40 series, featuring construction sizes and bases identical to classic incandescent lamps to enable easy replacements.

Light without shadowing

Decisive for the success of a lighting technology is whether the light from a lamp is perceived as being pleasant. This in turn depends on various factors, for example colour temperature and luminous intensity. The distribution of luminous intensity in the so-called far field is also important, meaning where light hits walls, floors or table surfaces for example. Of special importance in this respect is that light is distributed homogeneously and that minimum shadowing or linear structures are seen. The optics within LED lamps are responsible for this task. Because such optics can be seen from the outside with clear lamps, these are not only a functional element but must also be visually attractive. The optic also ensures that the "technology" of the lamp, meaning its LEDs and electronics, cannot be seen from the outside. Optics in the classic bulb-shaped lamps in the new Osram LED portfolio have been designed to largely exclude irregularities such as dark shadow lines in far field light and to achieve homogeneous light distribution, and this is achieved by the particular form of the plastic optic developed specifically for the new lamp generation. The design of the optic was developed with the aid of in-house programmed software due to these stringent technical and aesthetic requirements. Optics in the new Osram LED portfolio radiate at beam angles of up to 300° and also achieve a high level of uniformity in illumination.

retrofit lamp
Retrofit lamp from the new Osram portfolio.

Highly diverse lighting solutions

In addition to high levels of efficiency, the inherent diversity of the compact diodes is also advantageous, ranging from applications for video walls in sports arenas to the illumination of refrigerators. Because of their specific properties such as low heat generation and flat constructions, LEDs can be used in locations where other luminaires may only be installed in compliance with strict conditions – such as in fire protection applications. LEDs also generate no infrared or ultraviolet radiation, making them ideal for use in foodstuff counters and hospitals, and thanks to their tough constructions, LEDs are the ideal light source for applications exposed to high loads such as in the automotive sector. Osram LEDs also achieve very good colour rendering values of up to Ra 95.