What is the relationship between intensity of light and resistance?

The relationship between light intensity and resistance is fundamental to how many light-sensing devices work. Here's the explanation:

In photoresistors (LDRs - Light Dependent Resistors): - Resistance DECREASES as light intensity INCREASES - Resistance INCREASES as light intensity DECREASES

Why this happens: - Photoresistors contain semiconductor materials - When light photons hit the semiconductor, they provide energy that releases more charge carriers (electrons) - More charge carriers means better conductivity (lower resistance) - In darkness, fewer charge carriers are available, so resistance is higher

Mathematical relationship: For many photoresistors, resistance follows approximately: R ∝ 1/I (resistance is inversely proportional to light intensity)

Practical applications: - Automatic street lights - turn on when dark (high resistance triggers circuit) - Camera light meters - measure light for proper exposure - Solar panels - though they generate voltage rather than change resistance - Burglar alarms - beam interruption detection

This inverse relationship makes photoresistors incredibly useful for any application where you need to detect or respond to changes in light levels. The effect is immediate and quite dramatic - resistance can change from several megohms in darkness to just a few hundred ohms in bright light!