1000 watt bulb used for 1 hours would use 1KWh , is easy.
A bit off topic, but when I read the topic title I had to think about the following.
I thought that every electrical device could be revised… I will explain what I mean by that with an example.
You could use a electromotor as a generator, or a speaker as a microphone.
But what is a led? Is a led a light detector? is this true?
To a very small extent, yes, if you shine light into an LED, you would get current.
As I understand it they can make LEDs "sense" light by applying a reverse voltage to the led, which then builds up the capacitance at the LED junction, then once you disconnect positive from that LED you measure how long it takes for the electricity to bleed away. The more light there is the faster the electricity will bleed away.
For anyone looking for an easy experiment to do with this, check out this article in the arduino playground.
I think you cannot ask the specified question. LED light is not produce energy. LED light is requiring electric energy to produce brightness.