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.
A proper safelight for a given paper is one whose transmitted wavelengths are visible to the human eye, but invisible to the paper when exposed to them for the time it takes to process that paper. Whether that safelight is a purpose-built commercial device or DIY is pretty much irrelevent. The light is either safe for a given paper for a given period, or it isn't.
As mentioned earlier in post #27 (before this thread unfortunately went horribly off track), try performing the simple CD/DVD prism test with any safelight you are using. It's quick, it's easy, and it's cheap. I've found it to be a reliable indicator that you only need to look at to see if your safelight is transmitting any grossly non-safe wavelengths.
In other words, no matter what, you know that blues and greens are bad. Oranges that may fall slightly outside of a b&w paper's sensitized range are more problematic. But at least you can visually eliminate the obvious low-hanging fruit with relative ease before following up with a proper pre-fogged safelight test.
I've tested my 0C filters and they passed. This is the bottom line about the absolute need for testing - it accounts for other variables.
Originally Posted by Neil Poulsen
While this is undoubtedly true, in isolation it can only give the tester a binary result. Either the safelight is safe within the parameters tested, or it is not. It says nothing regarding why the safelight may not be safe. And more importantly, if the reason the safelight is unsafe might be an easily and inexpensively correctable flaw.
Originally Posted by David Brown
The case in point is, again, those expensive Thomas Duplex units. How many darkroom workers have in frustration replaced this unit with another different expensive unit because "it's too bright and it fogs my paper," when a quick visual check with a CD would have shown the real reason it was fogging paper had nothing to do with brightness? And that a $6.49 sheet of Roscoe theatrical filter would solve the problem without the need to junk the entire unit?
It's not that testing isn't the final word, it's that more information is always better.
Ken: I agree.
Originally Posted by Ken Nadvornick
If a safelight tests "safe", fine. However, if there's a failure, there could be any number of reasons why. 0C filters can fail, for instance, because they have faded to the point of being ineffective, or they may not be suitable for the paper in question, or it may be something else. It is entirely possible that a safelight test can fail when the safelight itself is OK, but there was stray light from the enlarger, or even another source that was not accounted for.