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Les langues disponibles
Optics
Fibroptonic
Ref : 202 012
ENGLISH
Figure 27: Curve representing the resistance R of the photoresistor in function of the
distance D from the light source (A: 40 W light bulb, B: 75 W bulb).
2.4 Note:
•
We obtain similar results if the light sources are fitted with colour filters.
•
The wattage of the bulbs (for example 40 W) is an electric power and not a
lighting power.
•
It is also possible to work at a given distance D with bulbs of different electric
power (25 - 40 - 60 - 75 - 100 - 150 W). In this case we measure the resistance R
in function of the electric power of the bulb and the flux emitted.
•
While taking a photo, the quantity of light that exposes the film is adjusted by the
diaphragm; it varies with the area of the diaphragm thus with the square of the
aperture. If the quantity of light is measured using a photoresistor, we deduce
that its resistance is proportional to the value of the diaphragm (a reminder of
these values: 16 - 11 - 8 – 5.6 - 4 – 2.8 – 1.4). This property is used in
photography.
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