why iodine-tungsten lamp volume small, brightnesshigh, the life is long?

The iodine-tungsten lamp principle is similar to the incandescentlamp, only is inside it breaks in the idodine vapor, the idodine vaporhas a nature, is in the low temperature (relative) with the tungstenand, if decomposes in the high temperature, like this, is located thelamp tube other parts, already sublimated the tungsten and fell, againdecomposed on the lamp silk, like this let the lamp silk not be ablebut fast to burn down because of the high temperature. This is theiodine-tungsten lamp compared to the why ordinary incandescent lamp tobe able to achieve a bigger power the reason.