General light measurements in lab
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|
The relation between these four (photometric) quantities is shown in the following drawing
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 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, it 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.