Question

The power ratings on lightbulbs are measures of what?

Answer 1

power rating indicate how much power they consume.

Explanation:

for a 100 watt bulb if it glow for 10 hours it will consume 1 KWH.
power is the rate of energy consumption.

Answer 2

Yes, you are correct, except for one miss-spelled word. The power ratings on light bulbs are measures of watts. --What??

Explanation:

One watt is the power required for a 1 Volt electrical potential difference to move 1 Amp of current through the light bulb, and is equivalent to 1 joule of energy per second. --What??
The power unit of watt is named after James Watt, a British inventor.

The power is the result of an electrical potential difference where an area with a high concentration of electrons (high voltage) is allowed to pass through the light bulb to get to an area of low concentration of electrons (lower voltage). The voltage difference causes a current of electrons to flow through the light bulb which is described as a number of Amps.

Power (watts) = volts (V) `xx` amps(A).
1w is described in the (SI) notation as 1 joule of energy per second.

So what? No, not what; the question is why. The reason for defining light bulbs by their power consumption was to give buyers a standard value by which they could choose the appropriate light output for a particular room size or application.
The customer could also readily multiply the power value by the price of a unit amount of power to figure out how much it cost to keep the light bulb turned on. An early conservation measure.

With the introduction of LED light bulbs, the power rating is gradually being replaced by the number of lumens of light output and the number of hours the bulb will last. So far, they still indicate the replacement power consumption in watts.

There are more watts here:
http://whatis.techtarget.com/definition/watt