The photocell sensor switch is fast gaining on the wide usage of the time switch in cases where lights must be ON during night times. It is very widely used in public lighting systems nowadays.
The photocell sensor switch works by using light sensitive cells somewhat similar to the solar cells. These cells are very sensitive to light and when there is light, the cell strips will expand enabling the strip to open two terminals akin to our normal switches. When it gets dark, it contracts to it’s normal length thereby closing the circuit again. With this capability it is able to switch on lights and apparatus when nightfall comes and switch them off automatically on sunrise.
The disadvantage of these switches is the user can never specify the time. It all depends on the sun and the availability of light source. Another disadvantage is because the cells are so light sensitive, the placement of these switches have to be taken into account when installing such a switch. If it is placed too near to the light and is able to absorb the rays from that light, the switch will not perform accordingly.
Those who has observed street lights switching ON automatically on a dark stormy days should not be surprised thinking that the local utilities company is so considerate to switch them on on days like this. It is the photocell sensor at play.
Photocell Sensor Switch other than widely used for public lighting, is also used by business signboards that lights up through the night. However due to it’s limited versatility, these kind of switches can never be used in industries where they need to time start certain machines or equipments.