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**Introduction to Measurement Quantities Training Level: BASIC**

Dr. Richard Young Optronic Laboratories, Inc.

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**Techniques & Types of Measurement**

Several types of light measurement are possible. These define WHAT you measure. For each type of measurement, there are several possible techniques. These define HOW you measure.

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**Techniques & Types of Measurement**

Techniques=how Photometry & colorimetry Radiometry Spectroradiometry Types=what Total Flux Angular Intensity At a surface At the source

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**Techniques & Types of Measurement**

Photometry & colorimetry Types Total Flux Angular Intensity At a surface At the source How does it look to humans? Quantities start with “photopic” or “luminous”

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**Techniques & Types of Measurement**

Radiometry Types Total Flux Angular Intensity At a surface At the source How much energy is produced? Quantities start with “radiometric” or “radiant”

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**Techniques & Types of Measurement**

Spectroradiometry Types Total Flux Angular Intensity At a surface At the source How is the energy distributed? Quantities start with “spectral” or “spectroradiometric”

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**Techniques & Types of Measurement**

Photometry & colorimetry Radiometry Spectroradiometry Types Total Flux Light emitted in ALL directions Quantities end with “flux”

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**Techniques & Types of Measurement**

Photometry & colorimetry Radiometry Spectroradiometry Types Angular Intensity Light emitted in SPECIFIED directions and angles Quantities end with “intensity”

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**Techniques & Types of Measurement**

Photometry & colorimetry Radiometry Spectroradiometry Types At a surface Light falling onto areas of an object Quantities end with “irradiance” or “illuminance”

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**Techniques & Types of Measurement**

Photometry & colorimetry Radiometry Spectroradiometry Types At the source Light emitted from areas within the source Quantities end with “radiance” or “luminance”

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**Quantities and Units unit: lumen unit: Watt unit: Watt/nm**

Photometry + Total Flux = Total luminous flux unit: lumen Radiometry + Total Flux = Total radiant flux unit: Watt Spectroradiometry + Total Flux = Total spectral flux unit: Watt/nm

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**Quantities and Units unit: candela = lumen/sr unit: Watt/sr**

Photometry + Angular Intensity = Luminous intensity unit: candela = lumen/sr Radiometry + Angular Intensity = Radiant intensity unit: Watt/sr Spectroradiometry + Angular Intensity = Spectroradiometric intensity unit: Watt/(sr nm)

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**Quantities and Units unit: lux = lumen/m² unit: Watt/m²**

Photometry + At a surface = Illuminance unit: lux = lumen/m² Radiometry + At a surface = Irradiance unit: Watt/m² Spectroradiometry + At a surface = Spectral irradiance unit: Watt/(m² nm)

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**Quantities and Units unit: candela/m² = lumen/(sr m²)**

Photometry + At a source = Luminance unit: candela/m² = lumen/(sr m²) Radiometry + At a source = Radiance unit: Watt/(sr m²) Spectroradiometry + At a source = Spectral radiance unit: Watt/(sr m² nm)

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Conversion of units The preceding units are SI units, currently the favored units by all National Standard Laboratories (NIST etc.) Sometimes older standards or conventions may require values to be reported in different units Quantities that are of the same technique and type can be converted by multiplying with a constant.

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Conversion of units Sometimes the conversion is because the quantities use different standard units E.g. using inches instead of meters for measuring length Sometimes the conversion is because the quantities use sub-units E.g. millimeters instead of meters

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**Conversion of units Common sub-unit prefixes**

femto (f), multiplied by 1E-15 pico (p), multiplied by 1E-12 nano (n), multiplied by 1E-9 micro (µ), multiplied by 1E-6 milli (m), multiplied by 1E-3 centi (c), multiplied by 1E-2 deci (d), multiplied by 1E-1 kilo (k), multiplied by 1E3 mega (M), multiplied by 1E6 giga (G), multiplied by 1E9 tera (T), multiplied by 1E12

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**Conversion to older units**

Conversion of units Conversion to older units Convert from to multiply by cd/m² lux (lm/m²) cd/in² footlambert ((cd/ft²)/p) Lambert ((cd/cm²)/p) stilb (cd/cm²) Footcandle (lm/ft²) phot (lm/cm²) 6.4516E-4 2.9186E-1 3.1416E-4 1.0000E-4 9.2903E-2

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