using arduino to read power useage using an LDR

the electricity meter in my house doesn't give me live power consumption figures it only blinks an LED every 1000th of a KWh.

so i need to make my arduino watch an LDR and measure the time between blinks.
then to work out the power consumption by doing
7.82 seconds between blinks * 1000 /60 ./60 = 2.17222
1000/2.17 = 460W

im not sure at all how to do math in arduino lol

any help would be appreciated.

lol i just worked out that i can just do time /3600 instead of all that

3600 / 7.82 = 460w

so i just need to time the LDR now

An LDR is slow, really sssss-llllll-ooooo-wwwwww.

Use a phototransistor or photodiode.
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