We encounter light-emitting diodes (LEDs) in many areas of life, where they offer clear advantages in comparison with conventional light sources. LEDs save energy, help preserve the environment due to their long lifetime, and do not contain mercury.
Based on their potential for higher levels of illumination, LEDs can increase safety on roads. LEDs are suitable for office applications, as well as ambient lighting at home. The automotive industry is relying more and more on LEDs. Last but not least, LEDs are used as a light source in liquid crystal displays, such as in TVs and mobile phones.
White light: The phosphor principle
White light is a combination of all colors in the visible spectrum and highly valued in day-to-day applications. However, LEDs are based on single semiconductor chips that emit a single color of light, and it is not possible to generate white light directly. To achieve white light, additional light-converting materials, phosphors, are needed.
Phosphors are micro-sized inorganic crystals and contain rare earth metals like yttrium and lutetium. Usually, a blue LED is combined with one or more light-converting materials. The luminescent phosphors are mixed in a matrix (for example, silicone) and placed around the LED chip. The converted light can produce any single color or a combination of colors and can generate all variations of white light.
The basic operating principle of a light-converting material is based on the physical principle of luminescence. Light is emitted after the activator within the phosphor crystals is excited by the energy of the blue or near UV light from the LED chip. This process transports an electron from the ground state to a higher energy level. During relaxation, the electron releases its energy by emitting light and returns to the ground state. The wavelength of the emitted light depends on the material and the activators and covers all colors from cyan to deep red. Combinations of different phosphors are used to emit white light.
High-performance lighting materials
isiphor® high-performance phosphor materials are essential to unleash the LED technology's full potential in terms of light quality, energy savings, and long lifetime. The quality and properties of the lighting material determine the efficiency of the LED and enable different color points (for example, correlated color temperature, CCT). The CCT describes the appearance of a white light source – from cold and neutral to warm white.
Our color-on-demand concept makes it possible to achieve the desired color points of LED and fulfill a wide range of customer requirements in a tailored solution.