The LED light spectrum

LEDs are not only dominating the lighting market, but also carving out a niche in more and more other applications. They impress with their energy efficiency, minuscule size and steadily increasing power.

The LED’s success story first gathered steam back in the 1960s. When the yield of light-emitting diodes was increased exponentially from less than one lumen per watt to more than 100 lumens. Initially, the only LEDs available emitted red or yellow light. However, the available spectrum has become much broader with the use of new semiconductor materials. First came green LEDs, then ultraviolet ones. Then, from the 1990s onwards, LEDs were developed that could efficiently generate light in the short-wavelength blue range. Nowadays, LEDs are available in practically all the colours of the rainbow. And that is not all: the luminous power of LED technology has dramatically improved since its infancy.

From garage door openers to driver monitoring

The scope of application for infrared LEDs (IR-LEDs) alone is impressive. They have long been used in remote controls for consumer electronics or in garage door openers, light barriers and motion detectors. In surveillance cameras, they enable razor-sharp image quality without the light emitted being perceptible to the human eye. Infrared LEDs in vehicles also help to promptly detect when drivers are nodding off, resulting in an extremely dangerous situation. Other vehicle applications for such high-performance IR-LEDs include seat occupancy sensors, night vision, close-range detection systems and blind-spot monitoring. And they are also used for communication. Using infrared light, data transfer rates of up to 12.5 Gbit/s can be transferred over short distances, with a rate of 1 Gbit possible at up to 30 metres.

Germs – illuminate to eliminate

There are also numerous applications for LEDs in the ultraviolet range at the “other end” of the visible spectrum. Compared to conventional UV light sources, UV-LEDs can be flexibly designed, consume little energy and boast impressively low manufacturing costs. UVA-LEDs emit light in a wavelength range of 315 to 400 nanometres. They are used to cure paints, coatings, varnishes and adhesives, for example.

UVB-LEDs emit light in a wavelength range of 280 to 315 nanometres. They are used for dermatological treatment of skin conditions or to promote plant development and increase crop yields.

The use of UVC-LEDs with their very high-energy radiation in a short-wavelength range of between 100 and 280 nanometres is a particularly hot topic just now.  They offer excellent bactericidal properties, enabling them to disrupt the DNA of micro-organisms. There are already solutions available on the market that use UVC-LEDs to eliminate any viruses and germs present on smartphones.

Yet the performance of the LEDs is now so high that even entire rooms can essentially be disinfected at the touch of a button. For example, manufacturer Binz will be launching the world’s first ambulance with a light-based disinfection solution in autumn 2020. In this setting, the UVC-LEDs are directly integrated into the modular, ceiling-mounted lighting panel inside the vehicle. This enables the entire cabin area of the ambulance to be disinfected very efficiently in as little as ten minutes. And during which both the surfaces and the air in the vehicle are treated.

Laser headlights

As the power of LEDs increased, they were increasingly used for applications requiring very bright light, such as car headlights. So the technology opens up new possibilities by enabling the light beam to be generated by an entire LED-matrix. Every LED in the matrix can be actuated individually based on the data supplied by a camera at the front of the vehicle. As soon as this detects other vehicles or road users, the control unit switches individual LEDs off or dims them. So they can avoid to dazzling other drivers, for example. The high beam remains simultaneously available in all other areas, improving visibility on the road. The latest development in this field involves replacing LEDs with laser diodes.

For instance, Audi has developed a headlight with blue laser diodes and a wavelength of 450 nanometres. They shine a beam onto a rapidly moving, three-millimetre micro-mirror based on silicon technology. This directs the laser beam onto a converter, which converts it to white light and projects it onto the road. The light can therefore be distributed precisely, while varying the dwell times in specific lighting zones enables variable brightness. Furthermore, the laser diodes can be switched on and off intelligently and in the blink of an eye as the mirror moves. This makes broadening or narrowing of the beam dynamic and highly variable. As a result, the road is always brightly lit without other road users being dazzled or blinded. The crucial difference is that the technology has even finer dynamic resolution and therefore an even higher degree of utilisation. Finally, this brings greater safety to road traffic.

The trend towards micro-LEDs

Alongside increasing power and an ever-growing range of available wavelengths, miniaturisation is the third significant trend for LED technology. Manufacturers of consumer electronics in particular are demanding LEDs that are not only suitable for use as backlights. But also for direct presentation of content in natural colours. This is especially the case for mobile devices. After all, LEDs have only really been able to be used as plain-white background lighting up until now. However, in order to display colours directly, three LEDs (red, green and blue) need to be grouped together to form each pixel in a colour display. Yet until recently, these LED groups were too large to be used in display screens.

New production processes now enable microscopically small LED arrays to be manufactured. Combining the necessary colours in a package just a few micrometres in size. These micro-LEDs have an edge length of less than 100 micrometres. Displays incorporating directly emitting micro-LED pixels are considered to be a disruptive development in the visual-display market. And they might even replace LCD or OLED technologies.


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