Just curious 2F...
Originally Posted by 2F/2F
Have you ever closely examined the output from this class of bulbs? I know when I did I found evidence of noticeable blue, green and other wavelengths leaking through or around those bulb's red paint and/or glass tinting.
Try looking at the bulb's reflection on the business side of a CD disc. That's also how I discovered the blue light coming from the red LEDs. I now make this simple check for all of the electronics in my darkroom that sport "red" indicator lights.
The worst offenders get opened up and have small squares of Rubylith applied. A few minutes spent and they then become completely safe for life.
It's also possible that the safelight bulbs to which you refer have been improved since my last look. And admittedly most people will not need 60 minutes of safe exposure. Often 5 minutes or so is sufficient for them.
But its nice to know there is no voodoo involved, and the situation can be easily discovered and mitigated.
excellent idea about the CD test.
So are you saying roscoe "fire" is good to cut blue & green and rubylith is good if you only need to cut blue?
I admit I don't fully understand wavelength & filtering yet but am getting there.
Originally Posted by brucemuir
Both will block transmission of blue and green. The difference is where in the visible spectrum they begin to allow transmission.
The Roscoe #19 Fire begins transmitting in the orange/amber region, also allowing everything lower in frequency (such as red) to pass. Since sodium orange is the color we really want from a Duplex (and nothing higher such as greens and blues) this material is a good match.
The Rubylith doesn't begin transmitting until you get down to red. It blocks everything higher than red, including orange/amber. Since the LEDs are mostly red to begin with, it doesn't matter that the material also blocks orange/amber. It's the red we really want.
The reason for choosing the Roscoe for the sodium light source is that it largely passes the desirable orange/amber, while the Rubylith does not. Using Rubylith on the sodium would unnecessarily darken the orange/amber output for no additional benefit, as both filters equally remove the undesirable greens and blues.
thanks for that.
I need to really study the spectrum so I can recall it and the relationships.
I remember I hopelessly guessed when this came up on a color theory exam once a few years back.
I am finally digesting CMY but that took me awhile also.
No, I have not closely examined the red lights, but they are pretty much all I have used until a week ago when I got a Thomas safelight with bona-fide filters. The only fogging I have had was from my cracked Brownie 0C safelight. I used to use it and the red lamps, but when it cracked and started fogging things, I just tossed it and went to all red. I get them at Freestyle; I'm not talking about "Halloween" lamps from the drug store.
Hi - went on the same quest about a month ago re bayonet dark red 'proper' darkroom bulbs - finally found some at Fotoriesel, Kent St. Sydney. phone 0292998833. Hope you're in Sydney and can go to their shop and pick them up - they're not listed on their product list on their website and so far I've had no luck getting them to post me a couple to Tassie..even though they confirmed they had heaps of them...good luck!
Trish in Tassie
Originally Posted by Ken Nadvornick
How about Rosculux #27 Medium Red?
Edit: Sorry. Nevermind. You answered that in post #13. I should read the whole thread before posting.