General light measurements in lab

Recommended product: specbos 1211-2 with two accessories (Integrating sphere, CIE 127 cond. A/B set up)

The following four basic quantities exist in light measurement and can be measured with a complete specbos 1211-2 system:

Quantity Symbol   Unit Simplified definition Used to characterise ...
Luminous flux lm "optical power" into all directions Halogen lamps, LEDs
Luminous intensity cd (basic unit) Point like sources as LEDs and lamps with reflector
Luminance cd/m2 Homogenious sources as monitors and video walls
Illuminance lx Brightness in a certain plane

A street lamp emits a Luminous Flux Φv and a part of this flux will be radiated into a certain angle Ω. The quotient is the Luminous Intensity Iv. This intensity creates the Illuminance/ Irradiance Ev on a certain area on the street and this value generates, in combination with the reflectivity of the street, the Luminance Lv, which is the visual impression for the observer of the street.

These four quantities can also be considered without connection to the human eye, but as physical quantities, then they are called radiometric quantities. Furthermore, each of them can be considered as spectral quantity (quantity per nm) or as total quantity (sum across the whole wavelength range).

An extended scheme with photometric and radiometric quantities can be found in Technical Note 20.

A spectroradiometer measures the spectral radiometric quantities in its operational wavelength range. This radiometric spectrum will be used afterwards to calculate all photometric, total radiometric and other quantities.

The basic unit specbos 1211-2 spectroradiometer can measure spectral radiance and spectral irradiance. It can be combined with an integrating sphere for flux measurements and with a CIE 127 set up to measure the radiant intensity of LEDs. Alternatively, the spectroscopy instrument can measure in this mode using its irradiance data and applying the inverse square law (see the application radiant intensity calculation using irradiance measurement).

Hence this specbos system covers all spectral spot measurement applications in the lab and is therefore best suited as a basic laboratory equipment.

The relation between these four (photometric) quantities is shown in the following drawing

Photometric quantities
Photometric quantities
Spectroradiometer JETI specbos 1211-2
Spectroradiometer JETI specbos 1211-2
specbos 1211-2 (with 500 mm integrating sphere, Radiant Flux)
specbos 1211-2 (with 500 mm integrating sphere, Radiant Flux)
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