A lamp bulb is rated 100w. Why is a time factor not included in the rating?
I found this on the net.
https://answers.yahoo.com/question/index?qid=20080817023758AAmRgMo
The rating of a lamp bulb typically refers to its power consumption, which is measured in watts (W). It indicates how much electrical power the bulb uses when it is turned on. This rating does not include a time factor because it represents the steady-state power consumption of the bulb.
To calculate the energy usage over time, you need to consider the time factor yourself. You can do this by multiplying the bulb's power rating (in watts) by the amount of time the bulb is turned on (in hours). This will give you the energy usage of the bulb in watt-hours (Wh) or kilowatt-hours (kWh).
For example, if you have a 100W bulb and you leave it turned on for 5 hours, the energy usage would be:
Energy usage = Power rating x Time
= 100W x 5 hours
= 500Wh or 0.5kWh
Including the time factor allows you to calculate the total energy consumed by the bulb and estimate its impact on your electricity bill.