I'm assuming you mean an LED light bulb since that is what we mostly use today.
An led light bulb uses very little power and my led light bulbs in my house use 9 watts per hour per bulb.
So to run my led light bulb for 1 hour it uses 9 watts so not even a penny to run the led light bulb for one hour.
If I run my led light bulb for 8 hours per day I would use 72 watts of electricity per day which still isn't much but if I run that led light bulb for 30 days it would be 72 watts x 30 which is 2,160 watts of electricity and my cost per kwh of electricity is 10 cents per kwh so that light bulb would cost me around 22 cents per month.
That's pretty cheap and certainly cheaper than the old light bulbs which would cost $2.00 to $3.00 per month per light bulb.
To run that led light bulb will only cost around $2.64 per year to run for 8 hours per day.