red safelight: colour temperature?

gandolfi · Jul 11, 2008

...:rolleyes:...

for our new photohouse we will make one of the windows into a red safe light.

we found a compagny that can make the glass in any colour we want, so here's the question:

does any of you know the colour temperature in red safelights? in Kelvin.

it has to be red as we work a lot with emulsions, that are sensitive to other tones..

the question is - how red? :confused:

ath · Jul 11, 2008

The concept of colour temperature doesn't work well with these filters.
Colour temperature assumes a continuous spectrum, the temperature gives the relative intensity of the different colours.
For red filters the cut off wavelength is a better measure.
My darkroom is lit by LED bulbs with approx. 650nm. This is safe with all my papers...
A dark red filter like a 29 has a cut off wavelength of 630nm and looks alot like a red darkroom filter.

Gary Holliday · Jul 11, 2008

You could look for safelight gels to place over the window. I imagine this would be far cheaper than specialist glass.

RobC · Jul 11, 2008

Graphic arts store should sell rubylith which can be bought in rolls with one side being adhesive. That should work to a point. But I rekon that you would need several layers to make it dark enough to work well.

http://en.wikipedia.org/wiki/Color_temperature

fschifano · Jul 11, 2008

I've made serviceable safelight filters for a 5x7 safelight with a 15 watt bulb used at least 3 ft. from the paper with 2 layers of rubylith and an appropriately sized sheet of window glass. Lexan would work just as well. Very inexpensive, and very effective.

Photo Engineer · Jul 11, 2008

A reading in Kelvin implies a tilted but continuous visible light source from 400 - 700 nm. In the case of a red light, you are only getting the portion from 600 - 700 nm and therefore the degrees Kelvin would be hard to establish.

If one considers bluish daylight to be around 5000 K or higher, and tungsten around 3000 K or lower, then the red light would have to be below that if you could asign a value at all.

I hope I got all of that correct. I'm winging it from memory. Too tired to hit the books.

PE

df cardwell · Jul 11, 2008

Lee Filters ought to be able to help.

http://www.leefilters.com/lighting/products/colours/

fschifano · Jul 11, 2008

gandolfi said:
...:rolleyes:...

for our new photohouse we will make one of the windows into a red safe light.

we found a compagny that can make the glass in any colour we want, so here's the question:

does any of you know the colour temperature in red safelights? in Kelvin.

it has to be red as we work a lot with emulsions, that are sensitive to other tones..

the question is - how red? :confused:

As I re-read your original question, the light bulb in my head switched on. Are you seriously considering using an outside window as a light source for a safelight? I'd be very careful about that. Daylight is a LOT of light and even the brightest safelights make only the tiniest fraction of that. I'd re-think that and make a way to block light completely from that window, then use a proper safe light.

gandolfi · Jul 11, 2008

fschifano said:
As I re-read your original question, the light bulb in my head switched on. Are you seriously considering using an outside window as a light source for a safelight? I'd be very careful about that. Daylight is a LOT of light and even the brightest safelights make only the tiniest fraction of that. I'd re-think that and make a way to block light completely from that window, then use a proper safe light.

would like to do that also, but alas - here in Denmark, we have to do this!
somebody, somewhere up in the system is afraid that my students will get disorientated, if they can't see out....
(I am willing to bet, that those guys never have been in a darkroom)

I've been in a darkroom with lots of these "windows"! I was very surprised, that it actually worked out fine! and thsy had at least 4 or 5 red glass windows!

I "only" have to have one....

Nicholas Lindan · Jul 11, 2008

gandolfi said:
does any of you know the colour temperature in red safelights? in Kelvin.

Color 'temperature' is the spectra of light emitted by a black-body of the given temperature.
http://en.wikipedia.org/wiki/Planck%27s_law

Safelight filters have _nothing_ to do with color temperature.

If you want to specify the transmission characteristics, they are available on the Kodak web site:
http://www.kodak.com/global/en/professional/support/techPubs/ti0845/ti0845.jhtml

(one more reason to support Kodak by buying their products ....????)

Nicholas Lindan · Jul 11, 2008

gandolfi said:
we will make one of the windows into a red safe light

Cover a regular window with "Rubylith". Rubylith is designed to mask film from being exposed by arc-lights, it will work for filtering sunlight and will work much better than any colored glass you are likely to find. You can find it in most artists' supply stores, and most likely the art department at your school will have some on hand. Several layers may be needed.

gandolfi · Jul 12, 2008

thanks all for your replys.

I feel a little stupid, but now more enlightened (sp?) (pun intended..)

Kilgallb · Jul 12, 2008

I took the minolta colour temperature meter from work into my dark room a few yars ago. The red safelight does not give enough light to register a colour temperature. The Lux value was well below 10.

At high noon in the summer in the northern hemisphere, (here in Calgary) we measured over 5000 lux. That is a lot of light.

Tom Kershaw · Jul 12, 2008

Perhaps you could convince those higher up that you don't need a window based safe light...

Tom

Mick Fagan · Jul 12, 2008

Would I be correct in assuming these same people, have requested windows be fitted to toilets?

Mick.

red safelight: colour temperature?

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red safelight: colour temperature?

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