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Three photoresistors with scale in mm Large CdS photocell from a street light. A photoresistor is less light-sensitive than a photodiode or a phototransistor. The latter two components are true semiconductor devices, while a photoresistor is a passive component that does not have a PN-junction. The photoresistivity of any photoresistor may vary ...
The ability of a lens to resolve detail is usually determined by the quality of the lens, but is ultimately limited by diffraction.Light coming from a point source in the object diffracts through the lens aperture such that it forms a diffraction pattern in the image, which has a central spot and surrounding bright rings, separated by dark nulls; this pattern is known as an Airy pattern, and ...
The most common sensor applications with a sampling rate of less than 1000 Hz are CCD or CMOS cameras. The sensor is partitioned into individual pixels whose exposure value can be read out sequentially. The position of the light spot can be computed with the methods of photogrammetry directly from the brightness distribution.
For instance, for an f/8 lens (= and %) and for green light (= 0.5 μm wavelength) light, the focusing spot diameter will be d = 9.76 μm or 19.5. This is similar to the pixel size for the majority of commercially available 'full frame' (43mm sensor diagonal) cameras and so these will operate in regime 3 for f-numbers around 8 (few lenses are ...
On the display unit, the measured optical power and set wavelength is displayed. Power meters are calibrated using a traceable calibration standard. A traditional optical power meter responds to a broad spectrum of light, however, the calibration is wavelength dependent. This is not normally an issue, since the test wavelength is usually known ...
The backscattered light has the same frequency as the transmitted light. There are a number of other distributed fiber sensing techniques that rely on different scattering mechanisms and can be used to measure other parameters. Brillouin scatter occurs due to the interaction between the light and acoustic phonons travelling in
Photodetectors may be used in different configurations. Single sensors may detect overall light levels. A 1-D array of photodetectors, as in a spectrophotometer or a Line scanner, may be used to measure the distribution of light along a line. A 2-D array of photodetectors may be used as an image sensor to form images from the pattern of light ...
Array detection of light, i.e. detecting light in a large number of independent detector pixels, is common in digital camera image sensors. However, it tends to be quite difficult in heterodyne detection, since the signal of interest is oscillating (also called AC by analogy to circuits), often at millions of cycles per second or more. At the ...