Why is a quartz-halogen bulb so bright

The second difference is the gas inside the bulb. Inside a normal light bulb, the gas is usually argon, but the gas inside the quartz halogen bulb is iodine vapour at low pressure, which has the ability to combine chemically with tungsten vapour. When the temperature is sufficiently high, the halogen 

This type of bulb is called a quartz-halogen lamp because iodine is a halogen element (from Group VII of the periodic table). 

More importantly, the addition of iodine makes it possible to operate the filament at a hotter temperature, with a higher proportion of the emitted light being visible light, although we still form much heat. 

Wien s law offers a simple relationship between the wavelength maximum k(max) and the thermodynamic temperature T  

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