'Rainbow' Light Source Developed

GAITHERSBURG, Md., April 29 -- The National Institute of Standards and Technology (NIST) has developed a "rainbow source" that can be tuned across the entire visible light spectrum, from red to blue light. This unique source exploits recent materials advances in LEDs of different colors. By mixing exact percentages of LEDs at different wavelengths of visible light with the desired brightness, the optical properties of the source (such as the color) can be changed and tailored for a particular application.

NIST's new portable "rainbow" source for calibrating color measurement instruments. In the background are a sampling of colors generated with the source. (Photo: NIST)

NIST's traditional light sources, such as incandescent lamps, are thermal. A blue thermal source would need to function at such a high temperature that components would melt. Lack of blue light sources introduces uncertainty when calibrating instruments that measure the color of things like bright stars or the open ocean. Knowing the exact color is important, NIST said, because it allows scientists to, for example, use remote satellites to judge the concentration of plant life in the ocean, which in turn affects global climate.

The NIST source uses commercial LEDs. NIST researchers characterized them and developed the packaging, electronics and software. In addition, the tunable light source is highly portable -- a sphere about 30 cm (1 foot) in diameter that weighs about two kilograms (five pounds). Battery operated versions have been developed for field applications.

NIST researchers described the invention at an Ocean Color Research Team meeting in Washington. The National Oceanic and Atmospheric Administration has ordered a simplified version of the rainbow source to reduce uncertainties in calibrations of a satellite that measures ocean color, as part of a program that monitors the carbon balance between the ocean and atmosphere. The source also could simplify color calibrations in industrial and other research applications.

More details will be presented at a meeting sponsored by NIST, the InterSociety Color Council and the Council for Optical Radiation Measurements, to be held May 10-14 at NIST in Gaithersburg.

For more information, visit: www.nist.gov