According to the International Energy Agency, around 2,650 Terra Watt hours each year are being used around the world for lighting. A level of consumption which offers an enormous potential for savings - in comparison to traditional light sources, modern light sources only need a maximum of just less than half of the energy. LEDs are one of highest energy efficient light sources available today consuming just 11% of the power used by normal bulbs. Even conventional energy saving lamps still consume twice as much as LEDs.

LEDs have further advantages in particular over fluorescent tubes and metal vapour lamps: firstly, they do not contain mercury, secondly, they are able to be turned on instantly, even in a very cold environment and in turn are easy to dim, which means lights in the street or in offices can simply be turned down depending on the time of day or level of usage. Thirdly, their low supply voltage with direct current predestines them for use in so-called solar lighting systems.

Light quality

Naturally an Edison incandescent bulb offers a gradient increasing wavelength distribution with a major chunk in the reddish spectrum, this leads to a warm colour tint that is commonly used in living areas. Compared to this white light LEDs are usually based on a blue diode covered with yellow phosphor - a cool colour tone going into the bluish is the result. In order to avoid this Sharp, for example, applies besides the yellow a mixture of red and green phosphor. As a result LEDs can be produced in a greater number of varieties, whereas specific colour temperatures can be changed by altering the amounts of red and green phosphor. The colour temperatures of the LEDs can also be ‘tweaked’ in the range from 2,200 to 11,500 Kelvin.

Illuminants from up to 4,000 K are typically used in the illumination of living areas while illuminants in the middle range of 4,000 – 5,000 K are applied to commercial applications, such as in offices, public buildings and factories. Cooler tones from 5,000 K and upwards are suitable where natural colour reproduction is required in , for example, medical applications, shop lighting and photography.

Over the different phosphor mixes white light LEDs reach a very high colour rendering index, which is important where the appearance of the illuminated objects should not be falsified by artificial light. For this type of application Sharp has developed a range of “high colour rendering” LEDs with CRI values of 80 and over – an important leap in quality when compared to previous products.

In addition to the comprehensive portfolio of white light LEDs for general lighting purposes, Sharp has also addressed the decorative lighting design market with a range of RGB and monochrome LEDs. The monochrome LED range includes LEDs in the standard colours – yellow, red, green and blue – as well as  three “fashion” colours in pastel tones called light blue, lemon yellow and purple.

The three dies on the RGB LED, red, green, blue, can be controlled separately. Specific current control allows a seamless transition throughout the entire colour spectrum from yellow to blue in a multiple of 100.000 nuances, and in turn providing some extraordinary design choices when it comes to architecture and interior design.

Modular design

The compact design of LEDs reduces luminaires to their elementary function: lighting. This provides designers with greater freedom and flexibility in the design of their luminaries. LEDs can be used with tremendous space savings and therefore do not necessarily dictate the overall form of the luminaires. This also means that the integration into, for instance, items of furniture, ceilings, car roof interiors etc., becomes easier to engineer. The smallest components in the Sharp’s white LED portfolio, for example, have an edge length of 1.6 x 0.8 x 0.2 millimetres. Even the Zenigata series, measuring 18 x 18 x 2 millimetres, is much more compact than a traditional light source.

However, LED modules do need to be understood as complex systems consisting of multiple elements: the light emitting diodes, secondary optics, heat sink and driving circuitries. All could have a significant influence on the light efficiency of the finished luminaires. To get the most of an LED Sharp works with a range of partners all of whom are capable of offering optimised solutions for a wide variety of different lighting applications such as the lens as well as the simpler equivalent, the reflector. Their design needs to ensures the light is distributed where it is really needed in order to keep the waste of light at a minimum.

In spite of their low input power, LEDs generate substantial heat which needs to be dissipated. Other than an incandescent bulb, which emits heat by radiation, LEDs need to dissipate heat by conduction via the LED packaging itself onto a heat sink. The rating of the heat sink will be determined by the total power of all LEDs used.

Sharp for instance guarantee a 40,000 hours lifetime (70% lumen maintenance level) at a LED package temperature (Tcase) of up to 80°C. As long as the heat sink performance is accurately adapted to the power which needs to be dissipated, it can be even utilised as a specific design element of the luminaires.

Cost-efficient

Despite the comparatively high initial costs, using LEDs as a light source do pay off throughout their total operational lifetime. According to industry calculations, LED based retrofit bulbs are already at an advantage after around 1,500 operating hours compared to electric filament lamps in terms of costs. Even in comparison to fluorescent tubes, the break-even point for costs is at around 8,000 operating hours, i.e. after a sixth of the operation lifetime of LED lights.

Considering the high maintenance costs for hard-to-access applications such as streetlights, where changing the light source is extremely time-consuming, the total cost savings generated by LEDs in comparison to traditional light sources accumulates to a total of around 38 percent. Given their energy-saving potential and long life cycle, LEDs are likely to rapidly gain in significance as light sources for general lighting.

The crucial elements that will help LEDs achieve a breakthrough into the market will be advantages like: long operation lifetime, compact form factor, high energy efficiency, no pollutants and finally a wide range of different colour temperatures.

Used as light sources in so-called LED based retrofit lamps, it is already possible today to substitute conventional light bulbs and low-energy light bulbs with LED lamps so that consumers can directly benefit from the advantages that the new light source technology is ushering in.

Andreas Biß is head of New Business Development at Sharp Microelectronics Europe

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