Language of Light

3.Instrumentation

3.1 RADIOMETER

Radiometer is a device used to measure the intensity of radiant energy. A majority of radiometers use only single photocell sensors. In order to measure radiation emitted from a specific spectrum or to incorporate the radiometer within a certain spectral response, an optical filter is normally used. Such optical filtering offers a simpler and more cost effective solution.
The industrial applications of radiometer mainly involve irradiance and radiance measurement. In order to quantify the radiation emission from source, radiance measurement is normally used. On the other hand, when the level of exposure is of concern, the irradiance or the integrated irradiance measurement is then carried out.

3.1.1 APPLICATIONS OF RADIOMETER

Radiometer is commonly used in industry to quantify light which is outside the visible spectrum, i.e., ultraviolet and infrared. Ultraviolet (UV) light is widely used in the industry for various applications, for example,
Curing of photoresists in semiconductor manufacturing
Curing of emulsions for printing or plate-making
Colour-fastness testing
Biological application

To conduct UV measurement by radiometer, either radiance or irradiance measurement, the spectral response (wavelength range and peak wavelength) should be specified to match the specific application.
Beside UV, infrared energy is also a common parameter in the field of radiometric measurement. Infrared measurement is useful as all material emits infrared radiation according to their thermal energies. Infrared thermometer utilises the principle of infrared radiance measurement to determine the temperature of object by non-contact means. Hence, such infrared radiometer is also commonly known as “Radiation Thermometer”. Different filters with specific spectral responses are used for different applications and temperature ranges. For more details about temperature measurement by infrared detection, please refer to our publication on ‘The Wonders of Temperature’.