LED - Solid State Lighting Assessment

Solid State Lighting Assessment Technical Information

Visible light is a form of electromagnetic energy, part of a spectrum that includes radio waves, X-rays, ultraviolet and infrared. Visible radiation is commonly called “light”, and is usually described by its wavelength, which is expressed in nanometers. One nanometer is one billionth of a meter, or roughly four ten-billionths of an inch. The relationship of light to other forms of energy is illustrated below. The human eye can only see a part of this energy spectrum – a very narrow band of wavelengths between about 380 and 780 nm. The hue we see as blue lies below 480 nm, green between approximately 480 and 560 nm, yellow between 560 and 590 nm, orange between 590 and 630 nm, and red appears at wavelengths above 630 nm.

Sources of light such as the sun, florescent lamps, tungsten-filament light bulbs and LEDs emit light that is composed of a combination of visible wavelengths. A curve showing the amount of each of the visible wavelengths emitted by a light source is known as its “spectral power distribution”. The hues we see of physical objects are directly affected by the spectral power distribution of their illuminating light sources. And more importantly for motion picture production, the hues seen by film stocks and digital motion picture cameras are also directly affected by the illuminant’s spectral power distribution in distinctly different ways than the human eye.