Describe how does an LDR detects light?

In the light, the resistance of the LDR is very low so it takes very little energy for the current to pass through the LDR, therefore the potential difference across the LDR is very low. Due to the potential difference being shared between components in series the potential difference across the lamp is large so the lamp lights up the screen. When the phone is held to someone ear the LDR is in darkness so it’s resistance rises sharply and it takes a great deal of current to pass through the LDR so the potential difference across the LDR is very high. While less energy is available for the lamp so its potential difference is very low making it very dim, turning the phone screen off.