Personal tools
Navigation






 

Photometry Light Measurement

Scroll down for Photometry-related light meter systems.

Unique human visual perception presents challenges in light measurement

Since the days of wax candles and oil lamps, man has attempted to quantify the light output from such devices in attempts to standardize production and ensure that one oil lamp was as bright as the next. As it turns out, this would prove to be a complicated problem. The visible light portion of the electromagnetic spectrum, sometimes called the optical spectrum, encompasses wavelengths approximately 400 to 700 nm containing most of the colors discernable to the human eye. However, the human eye is not equally sensitive to all wavelengths of light, being most sensitive to green at 555 nm under normal lighting conditions then to other wavelengths. Complicating attempts to measure human light perception is the individual variation in our ability to distinguish, describe, and reproduce color. A summary of average human visual perception of light would be required if any method for measuring it or reproducing its color was to be developed. Enter the CIE.

Human eye response research opens the door to photometry and colorimetry

The CIE or Commission internationale de l'clairage (International Commission on Illumination) is the international authority on matters involving light, illumination, and color. In an attempt to solve the problem of human color perception, the CIE in 1931 developed one of the very first mathematically defined color spaces, the CIE XYZ color space. The human eye contains receptors for short, middle, and long wavelengths, also referred to as blue, green, and red respectively, and therefore a color sensation would have to be defined as three parameters. A specific method for assigning three numbers, also known as tristimulus values, to represent each color is called a color space. Based on direct human eye measurement experiments performed in the 1920's, an RGB color matching model of human vision was developed and from this the CIE XYZ color space was derived. The central color matching function in calculating the CIE XYZ color space was the photopic luminosity function which represents the typical human eye response under normal lighting conditions and is referred to as the standard observer. Scotopic luminosity represents the typical human eye response in dark conditions where no color perception exists and mesopic luminosity is a combination of the photopic and scotopic functions where minimal color perception exists and represents the human eye response in dimly lit conditions. Having developed a basic color space based on a standard observer, we could then quantify the perceptual brightness of a light by direct measurement with devices that have the same response to light as that of the standard observer in a science now called photometry. Photometric light measurement is widely used in many industries to specify, monitor, and control the brightness of task, street, safety, automotive, and aerospace lighting to name a few. It is important to note that the CIE XYZ color space can only describe colors of light itself and not objects since the perceived color of an object will depend on the surface and color properties of the object itself, that of nearby objects, and the ambient and direct lighting properties but it did serve as the foundation for colorimetry, the science of color measurement or reproduction. Many additional color models, measurement techniques and instruments have developed subsequent to this groundbreaking research to objectively reproduce color in a wide variety of analog and digital media.

International Light Technologies covers the gamut of photometric measurement

International Light offers photometric measurement instruments that are unmatched in accuracy, sensitivity, and versatility for photopic and scotopic applications including illuminance and luminance as well as extensive color analysis via the powerful feature set of the ILT900 spectroradiometer.

 

Application Common Sources IL Spectral Range IL Product Options
Click Links Below
IL Measurement Range Units
ILLUMINANCE Office/home lights 220-1050 nm RPS900 SPECTRORADIOMETER Customized spectrum W/m2/nm

Lamp manufacturer 400-700 nm IL1700, SED033/Y/W 1.20e-3 to 1.20e+6 lux

LED's 400-700 nm IL1700, SCD110 3.33e-3 to 3.33e+6 lux

Flourescents 400-700 nm IL1400, SEL033/Y/W 5.98e-2 to 2.09e+5 lux

Halogen 400-700 nm IL1400, SCL110 1.67e-1 to 5.83e+5 lux
LUMINANCE Displays 400-700 nm IL1700, SED033/Y/R 1.16e-2 to 1.16e+7 cd/m2

LED's 400-700 nm IL1400, SEL033/Y/R 5.78e-1 to 2.02e+6 cd/m2

Signs 400-700 nm IL1700, SPD025Y 1.33e-2 to 1.33e+7 cd/m2


400-700 nm IL1400, SPL025Y 6.67e-1 to 2.33e+6 cd/m2


400-700 nm
IL1700, SED033/Y/P9/PIN 5.00e-1 to 5.00 e+8 cd/m2


400-700 nm
IL1400, SEL033/Y/P9/PIN 2.50e+1 to 8.75 e+7 cd/m2
PHOTOMULTIPLIER-BASED FOR VERY LOW LIGHT LEVELS Moonlight 400-700 nm IL1700, SPM068-1/YPM/QNDS3/W 8.70e-5 to 8.70e+2 (HIGH) lux

ILLUMINANCE AND LUMINANCE

Emergency lights 400-700 nm IL1700, SPM068-1/YPM/QNDS3/R 8.07e-4 to 8.07e+3 (HIGH) cd/m2

PHOTOPIC

Phosphorescence
400-700 nm IL1700, SPM068-1/ZPM/QNDS3/W 8.06e-5 to 8.06e+2 (HIGH) lux
SCOTOPIC

400-700 nm
IL1700, SPM068-1/ZPM/QNDS3/R 1.30e-3 to 1.30e+4 (HIGH) cd/m2
FLASH PHOTOMETRY Warning lights 400-700 nm IL1700, SED033/Y/L30 (> 25 ') Flash/Steady 1.39e-5 to 1.39e+4 lux lux & cd
LUMINOUS INTENSITY Runway lights 400-700 nm IL1400, SEL033/Y/L30 (> 25 ') Steady only 6.94e-4 to 2.43e+3 lux lux & cd
(Beam Candela)

400-700 nm IL1700, SED033/Y/H (< 25 ') Flash/Steady 2.02e-4 to 2.02e+5 lux lux & cd


400-700 nm IL1400, SEL033/Y/H (< 25 ') Steady only 1.01e-2 to 3.54e+4 lux lux & cd
SCOTOPIC LUMINANCE / ILLUMINANCE Signs 400-700 nm IL1700, SED033/ZCIE/W 3.33e-3 to 3.33e+6 lux

Displays 400-700 nm IL1400, SEL033/ZCIE/W 1.67e-1 to 5.83e+5 lux

LED's 400-700 nm IL1700, SED033/ZCIE/R 4.45e-2 to 4.45e+7 cd/m2<


400-700 nm IL1400, SEL033/ZCIE/R 2.33e+0 to 8.14e+6 cd/m2
* All Radiometers/Photometers/Spectroradiometers are NIST Traceable.
* If units of measure are not shown please contact us (empirical units also available i.e. fc, fL, nits, lm/ft2).
Document Actions
Copyright © 2002-2010 International Light Technologies Inc. All rights reserved.




Built by Stellar Link