Photoresistor vs. Photodiode: Key Differences Explained

This article compares photoresistors and photodiodes, highlighting their differences, advantages, and disadvantages.

What is a Photoresistor?

Introduction:

• A photoresistor is a passive component whose resistance changes in response to light.
• It’s typically a disc-shaped component with two leads, as illustrated in Figure 1.
• When light strikes the disc’s surface, the resistance between the leads decreases.

In darkness, the resistance can be as high as 10 MOhms, while in bright light, it can drop to as low as 500 Ohms. Photoresistors are non-polarized, meaning they offer equal resistance in both directions, making them suitable for both AC and DC circuits.

One common application of a photoresistor is as a light-sensitive variable resistor. The resistance decreases as the intensity of incident light increases, a phenomenon known as photoconductivity. Various circuit symbols represent photoresistors. They come in different sizes, ranging from 5 mm to 25 mm in diameter. Photoresistors can be used to generate variable voltage depending on the intensity of light.

What is a Photodiode?

A photodiode is a type of photodetector that converts light into either current or voltage. It operates in reverse bias, where the electric field across the p-n junction sweeps mobile charge carriers to their respective majority sides, forming a depletion region.

This barrier prevents the flow of majority carriers, allowing only minority carriers to pass, resulting in a small leakage current.

The figure above shows the photodiode symbol and a sample part from OSRAM.

Difference Between Photoresistor and Photodiode

The following table summarizes the key differences between photoresistors and photodiodes: