Pp Ldr Camera Control

Using an LDR to control the brightness of a photograph

The resistance depends upon the amount of light

The light must be right to take good pictures

Too little

Too much

Photographers need to control the amount of light used to take the picture Most modern cameras do this automatically

Really good cameras also allow you to do it yourself so you can get better pictures or clever effects

The resistance of an LDR gets less as more light falls on it

Resistance / Ohms

They can do this using Light Dependent Resistors LDRs

Dim > High Resistance Bright > Low Resistance

Brightness

The light detector is mounted in the front of the camera

The amount of light can be controlled by adjusting the size of the aperture (shown in red)

It can also be controlled by how long the aperture is open for light to enter

The battery, LDR & resistor are wired in series The LDR and resistor share the cell’s voltage As the light intensity changes, the voltage across the resistance changes The resistors voltage controls the brightness Aperture opener and Closer

V

B

= VLDR

+

VR

LDRs also have other uses where the brightness of light controls something happening Another example is controlling streetlights so that they turn on when it gets dark.