Have we really defined the "proper" safelight?
I used a couple of 0C Kodak safelight (standard 5.5") for years, until I took John Wimberley's darkroom workshop. He's ADAMANT about stray light in his darkroom and preventing any fogging whatsoever of highlights. He tested the OC filters, and they failed. (I think that his tested is related to the one described by A.A.)
The Red Series 1 Kodak filters passed his test, so that's what he uses. I followed his recommendation and replaced the OC's I've been using.
With that said, purchasing these new is expensive. I waited until two Series 1's became available on EBay for modest prices. They don't come up that often.