Photocells are sensors that allow you to detect light. They are small, inexpensive, low-power, easy to use and don't wear out. For that reason they often appear in toys, gadgets and appliances. They are often referred to as CdS cells (they are made of Cadmium-Sulfide), light-dependent resistors (LDR), and photoresistors.
Photocells have a resistor that changes its resistive value (in ohms Ω) depending on how much light is shining on it. Each photocell sensor will act a little differently than the other, even if they are from the same batch. The variations can be really large - 50% or higher. For this reason, they shouldn't be used to try to determine precise light levels in lux or millicandela. Instead, you can expect to only be able to determine basic light changes.
Photocells are a great choice for scenarios like these
To test and see if it’s light or dark out
If there something in front of the sensor (that would block light)
If there something interrupting a laser beam (break-beam sensors)
Which of multiple sensors has the most light hitting it
What are Octopus Electronic Bricks?
Pi Supply Octopus Electronic Bricks can be used to build electronics projects just as easy as piling bricks. You can also connect Arduino compatible boards easily with various digital, analog and I2C/Uart interfaces. The breadboardless connections let you connect expansion modules like potentiometers, sensors, relays, servos, buttons in a plug and play way.