Photometry

Unique human visual perception presents challenges in light measurement

Please SCROLL DOWN to review our PHOTOMETERS for use in all types of photometric measurements.

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 discernible 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 (CIE overview is continued at the bottom of this Web page).

 

 

International Light Technologies covers the gamut of photometric measurement

International Light Technologies (ILT) 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 either the ILT950 or ILT550 spectroradiometer.

 

Need Light Measurement Applications Help? Click on THIS LINK to Contact an ILT Light Measurement Expert

 

Application Common Sources Spectral Range ILT System Options
Click Links Below
Measurement Range Units
ILLUMINANCE Office/Home Lights; Lamp Manufacturer; LEDs; Fluorescents; Halogen 380-780 nm ILT350 ILLUMINANCE SPECTROPHOTOMETER 20-10,000 lux & colorimetry
    200-1100 nm ILT950 SPECTRORADIOMETER Customized spectrum W/m2/nm
    250-900 nm ILT550 SPECTRORADIOMETER Customized spectrum W/m2/nm
    400-700 nm ILT5000 Photometer, SED033/Y/W Detector 8.34e-4 to 1.67e+6 lux
    400-700 nm ILT1700 Photometer, SED033/Y/W Detector 1.20e-3 to 1.20e+6 lux
    400-700 nm ILT1700 Photometer, SCD110 Detector 3.33e-3 to 3.33e+6 lux
    400-700 nm ILT2400 Photometer, SED033/Y/TD Detector 3e-2 to 5e+5 lux
    400-700 nm ILT2400 Photometer, SCD110 Detector 9e-2 to 1e+6 lux
NEW! EML Equivalent Melanopic Lux LED Based Lamps, Signs, Headlights, Displays, TVs, etc. 400-600 nm ILT2400 Photometer, SED033/EML/TD Detector 5e-9 to 9e-2 W/cm2 & lux
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LUMINANCE (Brightness Intensity Systems) Displays; LEDs; Signs 400-700 nm ILT5000 Photometer, SED033/Y/R Detector 6e-3 to 1e+7 cd/m2
    400-700 nm ILT1700 Photometer, SED033/Y/R Detector 1.16e-2 to 1.16e+7 cd/m2
    400-700 nm ILT2400 Photometer, SED033/Y/R Detector 3e-1 to 5e+6 cd/m2
    400-700 nm ILT5000 Photometer, SPD025Y Detector 6.67e-3 to 1.33e+7 cd/m2
    400-700 nm ILT1700 Photometer, SPD025Y Detector 1.33e-2 to 1.33e+7 cd/m2
    400-700 nm ILT2400 Photometer, SPD025Y Detector 4e-1 to 6e+6 cd/m2
    400-700 nm ILT5000 Photometer, SED033/Y/PIN4 Detector 5e-1 to 2.5e+8 cd/m2
    400-700 nm ILT1700 Photometer, SED033/Y/PIN4 Detector 5.00e-1 to 5.00 e+8 cd/m2
    400-600 nm ILT2400 Photometer, SED033/Y/PIN4 Detector 2e+1 to 2.5e+7 cd/m2
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FLASH PHOTOMETRY; LUMINOUS INTENSITY; BEAM CANDELA Warning lights; Runway Lights 400-700 nm ILT5000 Photometer, SED033/Y/L30 Detector
(> 25') Flash/Steady
7e-6 to 3e+3 lux lux & cd
    400-700 nm ILT1700 Photometer, SED033/Y/L30 Detector
(> 25') Flash/Steady
1.39e-5 to 1.39e+4 lux lux & cd
    400-700 nm ILT2400 Photometer, SED033/Y/L30 Detector
(> 25') Flash/Steady
3e-4 to 3e+3 lux lux & cd
    400-700 nm ILT5000 Photometer, SED033/Y/H Detector
(< 25') Flash/Steady
2e-4 to 9e+4 lux lux & cd
    400-700 nm ILT1700 Photometer, SED033/Y/H Detector
(< 25') Flash/Steady
2.02e-4 to 2.02e+5 lux lux & cd
    400-700 nm ILT2400 Photometer, SED033/Y/H Detector
(< 25') Flash/Steady
9e-3 to 9e+4 lux lux & cd
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CANDELA/LUX MULTI-POINT SIMULTANEOUS MEASUREMENT SYSTEMS Flashing/Pulsed or CW Light Soureces 400-700 nm ILT6000 Photometer, SED033/Y/TD Detector
(< 25') Flash/Steady
8e-5 to 5e+5 lux & cd
    400-700 nm ILT1010/TD
(< 25') Flash/Steady
3e-2 to 5+5 lux & cd
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SCOTOPIC LUMINANCE / ILLUMINANCE Signs; Displays; LEDs 400-700 nm ILT5000 Photometer, SED033/ZCIE/W Detector 2e-3 to 1e+6 lux
    400-700 nm ILT1700 Photometer, SED033/ZCIE/W Detector 3.33e-3 to 3.33e+6 lux
    400-700 nm ILT2400 Photometer, SED033/ZCIE/W Detector 9e-2 to 1e+6 lux
    400-700 nm ILT5000 Photometer, SED033/ZCIE/R Detector 3e-2 to 2e+7 cd/m2
    400-700 nm ILT1700 Photometer, SED033/ZCIE/R Detector 4.45e-2 to 4.45e+7 cd/m2
    400-700 nm ILT2400 Photometer, SED033/ZCIE/R Detector 1e+0 to 2e+7 cd/m2
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* 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).

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CIE Overview (continued)

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.