In the US, I believe we would say/spell it as "co-louvered." Fresnel lenses in the US with black painted risers were rare but not impossible, although most had a pebble or hex finish on the flat side to further soften/diffuse the beam. For a time, particularly with 8"+ ERSs, the P.C. lens was too expensive, heavy, prone to breakage so step lenses were introduced. Kliegl in particular was notorious for putting them in every ERS. At least Century, Altman, and Capitol only used them where they had to. In theory, removing the unneeded glass should lead to higher transmission. In practice, since the risers needed to be coated in black ceramic paint to control errant spillage, ERSs with step (stepped) lenses projected a bulls-eye target onstage. And R119, 132, and 140 hadn't been invented yet.
