a bulb is rated 220 volt 100 volt what does this mean
Answers
Electrical appliances are designed for particular power output/consumption based on system voltage. This light bulb is designed to be used in a country or system that uses 220 volts AC in ordinary end user applications, as in a home. Iceland is such a country, in contrast to the USA which uses 110V AC in these relatively low power demand uses. Now power (Watts) is the combination of current (amperage) and voltage. So the 100 W lightbulb has a resistance that permits a current at 220V that gives a power consumption of 100 Watts. If you used this light bulb in a 110V system it would use only half the power and produce less light.
220 Volt systems are considered somewhat riskier than 110V systems however they allow these systems to use thinner conductors, saving costs, or to power higher power appliances. Icelandic tea kettles come to a boil faster than their 110V cousins in North America.