| 摘要 |
PROBLEM TO BE SOLVED: To suppress the breakage of glass for a lamp in a process where temporarily formed glass is further worked. SOLUTION: The glass composition for a lamp has a composition containing, by mol %, 70 to 85% SiO2 , 12 to 17% R2 O, and 2 to 8.5% MO (R is at least one kind selected from Li, Na and K; and M is at least one kind selected from Mg, Ca, Sr, Ba, Zn and Pb), and satisfying CaO+MgO>BaO+SrO, and whose brittleness index value B obtained by a Vickers hardness test is 7,000 m<-1/2> . Preferably, the contents of SrO are controlled to be 0 to 0.5%, and BaO to be 0.1 to 1%, and, more preferably, K2 O>Na2 O is satisfied.
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