1. Introduction to Measurement Quantities Training Level: BASIC
Dr. Richard Young
Optronic Laboratories, Inc.

2. 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.

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

4. 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”

5. 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”

6. 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”

7. Techniques & Types of Measurement
Photometry & colorimetry
Radiometry
Spectroradiometry
Types
Total Flux
Light emitted in ALL directions
Quantities end with “flux”

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

9. 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”

10. 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”

11. 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

12. 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)

13. 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)

14. 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)

15. 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.

16. 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

17. 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

18. 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