A photocell changes its electrical conductivity when light shines on it.
When it senses light, electricity flows through it, but when it is dark, and no light shines on it, almost no electricity flows through it.
A photocell changes its electrical conductivity when light shines on it.
When it senses light, electricity flows through it, but when it is dark, and no light shines on it, almost no electricity flows through it.