"These mini-pyramids scatter 73% of the light that hits them, which gives the material that frosted look. But despite that, it’s surprisingly more transparent to light than regular glass – 95% transmittance compared to the usual 91% of most glass. The team says that makes for a more comfortable lighting not just for people, but plants as well."

Clearly, because they're qualifying its frosting effect - it's frosted, which inhibits the passage of vision, but counterintuitively, it does not stop the transmittance of light, so it doesn't darken a room.