Whenever there is observed movement of charge carriers in a substance, there is an electric current. Current is measured in the terms of the number of electrons or holes passing single point in 1 second.
Usually, many charge carriers go past given point in 1 second, even if the current is small. In a household electric circuit, a 100-watt light bulb draws a current of about six quintillion charge carriers per second. Even the smallest mini-bulb carries quadrillions of charge carriers every second. It is ridiculous to speak of a current in terms of charge carriers per second, so generally it is measured in coulombs per second instead. A coulomb is equal to around 6,240,000,000,000,000,000 electrons or holes. A current of 1 coulomb per second is called as ampere, and this is the standard unit of electric current.
When a current flows through a resistance-and this is the case because even the best conductors posses resistance-heat is generated. At times light and other forms of energy are emitted as well. A light bulb is designed deliberately so that the resistance causes visible light to be generated. Even the best incandescent lamp is inefficient, generating more heat than light energy. Fluorescent lamps are better. They produce more light for the given amount of current. Or, to put it the other way, they require less current to give off a certain amount of light.
Electric current flows very fast through any resistor, conductor, or semiconductor. Actually for most practical purposes you can consider the speed of current to be the same as the speed of light: 186,000 miles per second. In fact, it is a very less.