Photometer
From ArticleWorld
A photometer is an instrument that is used to make measurements of the various parameters associated with the visible range of the electromagnetic spectrum. The comparison may be done by using either visual or photoelectric methods.
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Classification of photometers
Photometers may be classified under two categories:
- Laboratory photometers:
Such photometers are used for conducting optical experiments under laboratory conditions. They are usually fixed in position and are used by scientists to come up with results of high accuracy.
- Portable photometers:
Such photometers are used in the field and are designed for more rough use. They give results of lower accuracy. Photometers, either laboratory or portable, are further divided into two subclasses: Visual and photoelectric.
Measurements taken by photometers
Photometers, depending on their functionality are used to take measurements of the following important parameters:
- Luminous intensity, which is measured in candelas or candlepower.
- Luminous flux.
- Illumination, also termed as illuminance.
- Luminance, which is a measure of photometric brightness.
- The distribution of light.
- The reflectance and transmittance of light.
- The color of light.
- Spectral distribution.
- The level of visibility in the surroundings where light is incident.
Applications of photometers
Apart from the scientific research applications of photometers, these devices find applications in the following areas:
Astronomy
Photometers are used in astronomy to measure the brightness of stars and other celestial objects. A photoelectric photometer is used to record the electric current that is generated when light from a celestial body falls onto a photosensitive surface. An electric current which is given out is then amplified to measurable levels by a photomultiplier. It is possible to measure the intensity of light at various points of an extended object like a distant nebula or a galaxy with the help of CCD detectors or an infrared array.
Sport
The photometer, also referred to as a light meter, is commonly used by umpires in international cricket matches to ascertain if the intensity of light is suitable for continuation of play in overcast or poor light conditions.