Mercury-free arc tube for discharge lamp unit

摘要

A mercury-tree arc tube for a discharge lamp unit including a closed glass bulb in which main light emitting substances of NaI, ScI 3 , and ScBr 3 and buffer substances of InI and ZnI 2 are enclosed together with Xe gas, and wherein an amount of enclosed ScBr 3 is in a range of about 5 wt% to about 24 wt% relative to a total weight of the substances enclosed in the closed glass bulb. The mercury-free arc tube may also include a shroud glass tube, which is surrounds the closed glass bulb and a pair of electrodes, which are disposed to be opposed to each other in the closed glass bulb.