A bulb with an inner quartz bulb which holds a tungsten filament . Usually the
inner bulb contains an inert gas such as iodine or one of the other five halogen gases. The use of a halogen gas prevents the bulb from turning black and thus reducing the amount of light output.Because this type of bulb requires intense heat, a quartz inner bulb is needed instead of glass. As a result, the quartz-halogen bulb produces more light per watt of electrical power. When replacing a quartz-halogen bulb , it is important not to touch the outer bulb with your fingers. The moisture and oils deposited on the glass will cause the glass to break under the high temperature.