Color rendering is very important when reading topographical maps with an LED flashlight or when an electrician needs to discern wire colors with an LED flashlight. In museum illumination, a high color rendering index is vital to the perception of color in paintings and other works of art.
When poor color rendering is evident when illuminated by white LED’s, it is because the green and red components are weak. Sunlight has output at all visible wavelengths with relatively gradual and smooth transitions when graphed as power vs. wavelength; all colors can be determined equally well in sunlight. With fluorescent lamps and phosphor-pumped white LED’s there is not the smooth output-versus-wavelength curve or transition that is found with natural sunlight, hence the colors viewed by the eye will not be true.
The LED chips have been available for many years and the concept demonstrated by many different LED companies. The problem has been color stability. Red and amber LED chips have a high wavelength and intensity shift over ambient temperature compared to green and blue LED chips. Without proper compensation over temperature shifts, the white light will become warmer (more red) at low temperature and colder (more blue) at high temperature.
Within the last few years LED controllers specifically designed for multicolor LED arrays have come onto the market at a reasonable price. With the introduction of these controllers, the “light engine” market for multi-color LEDs has increased significantly. These controllers also allow for creating any color of interest from violet to red.
Advantages & Applications
LEDs for monochromatic applications have huge advantages over filtered lamps; the wavelength spectra is better defined than what can be achieved with a white light source and filter. For general lighting applications, the energy savings can easily be 100 times the cost of using a filtered incandescent lamp. This creates huge dividends in applications such as architectural lighting and traffic signals. Low-power portable highway LED signage can easily be powered by a small solar panel instead of a large generator, offering a distinct advantage.
LEDs are more reliable than lasers, generally cost less, and can be driven with lower cost circuitry. The European Union has now joined with the U.S. in classifying LEDs as a separate entity. Fortunately, LEDs do not carry the same eye safety concerns or warnings that lasers and laser diodes often have. On the other hand, LEDs cannot be made into extremely small, highly collimated and optically dense spots. In applications where extremely high power density within a small area is required, a laser is almost always required.
For more information, visit: Light Emitting Diodes - A Primer