A quick look at photoresistors 

Good tutorial. Another common way of detecting light is to use an LED as a sensor ! Not a lot of people are aware that they can also act as simple photo diodes. Lots of examples on RU-vid of their application in this way :)

Another thing about the photoresistors, is that majority of them, being of usual Cadmium Sulfide, are actually slow at reacting to anything compared to photodiode and phototransistor which is easily discoverable with LED flashlight that you know has higher frequency PWM (beyond 10kHz) and an oscilloscope.

you are exlant man thank you

Awesomesauce Paul, two videos on the trot with a new gadge, a project and little or no cost, thank you kindly - my marriage is saved, again... 👍🏻💡🐍

Thank you for this great video my friend.

I am trying to figure out what is the best resistance values and size for a sun tracker.. using Arduino.

Simplest method to implememt this application. Also, and correct me if I'm wrong, but the slight increase in LED brightness when u first move your hand over is due to the *proportional* voltage increase in the trans base? Nice effect compared to strictly on/off from a non-pwm pin.

Hi. I did it without the transistor. What’s the use of the transistor in this setup?

Thanks for another fun circuit. I seem to remember something like this in one of Forest Mimms books. Cool stuff.

What are they made of in Le Europe?

Do you need to use a transistor?

How could I build this circuit myself??

If you have enough of these connected together in parallel would it work as a solar panel?