Page 51 - Sensors and Control Systems in Manufacturing

The Role of Sensors in the 21st Century

1.9 The LED Color Chart 15
The LED color chart in Table 1.2 does NOT represent what the LED
light carries. This chart is only to be used as a reference for the vari-
ous types of LEDs being manufactured today, and to show what their
basic properties are.

1.10 The Color Rendering Index (CRI)
The color rendering index (CRI) is a measure of the quality of light.
A measurement of the amount of color shift that objects undergo
when lighted by a light source as compared with the color of those
same objects when seen under a reference light source of compa-
rable color temperature. LED light CRI values generally range from
60 (average) to 90 (best). High CRI equates to sharper, crisper, more
natural-colored pictures, while at the same time reducing glare
(Fig. 1.8).
A measure of the color of a light source relative to a blackbody at
a particular temperature expressed in degrees Kelvin (K). Incandes-
cent lights have a low color temperature (approximately 2800K) and
have a red-yellowish tone; daylight has a high color temperature
(approximately 6000K) and appears bluish (the most popular fluores-
cent light, Cool White, is rated at 4100K). Lamps with color tempera-
tures below 5000K tend to be more yellow/red, lamps rated between
5000 and 6000K are viewed as white, while lamps above 6000K tend
to have a blue cast.

1.10.1 The Foot-Candle
The foot-candle unit is defined as the amount of illumination the
inside surface of an imaginary 1-foot radius sphere would be receiv-
ing if there was a uniform point source of one candela in the exact
center of the sphere. Basically, the amount of light that a single candle
would provide to a 1-foot radius sphere.

1.10.2 Full Spectrum
A light bulb or lamp that produces a light spectrum that covers the
entire range of visible light (400–700 nm) without gaps in its spectral
output. White LEDs are inherently a full spectrum light source.

1.10.3 Intensity
Is a measure of the time-averaged energy flux or amount of light strik-
ing a given area. For bulbs alone, this is measured in terms of lumens,
while for lighting fixtures it is measured in lux (lumens/sq. meter).