collect the light bill
The Spanish phrase 'cobrar el recibo de la luz' translates into English as 'collect the light bill'. It is a common phrase used in Spanish-speaking countries to refer to the action of receiving payment for the electrical services provided. This could refer to a professional who works collecting these payments, or it could also be used in a more general sense to indicate the necessity to pay for your electric bill.
We have to pay the light bill before Friday.
This sentence suggests that the speaker and possibly other individuals have the responsibility of paying the electricity bill before the specified day in the week, which is Friday.
If you don't pay the electricity bill on time, you will be without electricity.
This is a warning or advice that the immediate consequence of not making prompt payment of the electricity bill is disconnecting of the power supply.
Have you been able to pay the electricity bill this month?
This sentence is a question inquiring whether the second party managed to pay for the electricity bill of this particular month.