The oldest and most widely used method of converting electricity into light is to connect a metallic resistor or a filament into an electric circuit. Filaments are usually made of wolfram, which is the most heat-resistant of all the known metals. When the filament heats up, it begins to radiate light. Light bulbs that produce light this way are called incandescent light bulbs. 

Because the function of the incandescent light bulb is based on a heat resistor, it produces more heat than light. This means that a lot of the electricity used to produce light is wasted. This is why incandescent lightbulbs are rarely used today.


Incandescent light bulbs.