Eight ranges, one coating line

VLT — visible light transmission. The one number a tenant feels immediately. It sets how dark the room reads, and it is the only figure that appears on both the film datasheet and the glass specification, which is why it is the easiest to check and the easiest to mis-sell. A 35% film on 6 mm clear glass and 35% on a body-tinted unit do not produce the same room.

SHGC — solar heat gain coefficient. The share of incident solar energy that ends up inside the space, as heat. This is the number that predicts cooling load. It is not the same as TSER, which measures rejection rather than admission, and it is not the same as IR rejection, which describes a slice of the spectrum.

TSER — total solar energy rejected. A convenient summary, computed from reflectance, absorption and transmission across the solar spectrum. Useful for ranking films against each other on the same glass. Useless as a cooling-load calculation on its own, because absorption is partly re-radiated inward.

IR rejection. Almost always quoted at 900–1,000 nm, a narrow band near the top of the near-infrared. A high figure here is easy to produce and is the most abused number in the category. It tells you about one band; it does not tell you what the film does at 1,500 nm, and it does not predict SHGC.

UV rejection. Typically above 99% for any film with a UV absorber, which makes it the least differentiating figure on the sheet and the most useful thing to say to a client who is worried about fading — with the caveat that visible light and heat cause fading too.