For 10 points, name this substance that is usually incorporated into buildings by windows.
This medium is used extensively in the artwork To Piet Mondrian, Who Lacked Green, which was created by Dan Flavin, an artist who specializes in using it. In collaboration with the MAS, John Bennett and Gustavo Bonevardi created a memorial that displays 88 columns of it. Two slabs of silky smooth concrete that are cut at a 15 degree angle comprise an (*) Osaka chapel named for this entity, which was designed by Tadao Ando. The construction of clerestories and oculi were medieval ways of incorporating it into buildings. On September 11 of every year since 2001, two lines of it are shot into the sky as a memorial to those who died. For 10 points, name this substance that is usually incorporated into buildings by windows.
This medium is used extensively in the artwork To Piet Mondrian, Who Lacked Green, which was created by Dan Flavin, an artist who specializes in using it.
light [Accept any type of light, such as "green light" "sunlight" or "natural light," etc.]