Quote Originally Posted by David Brown View Post
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.
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.

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.