a couple questions about light bulbs

weasel · Nov 17, 2020

Finally after about ten years im finnaly setting up my permanent darkroom, yeah! I have a couple questions about bulbs for my safelight, and my enlarger that I have been unable to find concrete informatiion for.
My safelight is a standard kodak model D. It is listed as taking a 25 watt bulb max. My question is, is that because of the light level, or the heat level? Can I put a brighter LED in, and if so does the temeprature range of the light matter?
Same question for my leitz focomat 1c. If I want to put an led in it, will the temperature range of the bulb affect multigrade filters, and if so, what temperature range should the bulb be?

Donald Qualls · Nov 17, 2020

The limitations on enclosed fixtures are usually for heat reasons; a brighter LED won't overheat your safelight. On the other hand, "safe" is relative; if you make your light brighter, you may get safelight fogging. For instance, Kodak specifies a distance from the work, as well as wattage (=> lumen output) and filter; if you move the light closer, it's brighter on the easel or trays, and even in a low-sensitivity wavelength, it may fog.

Put another way, you can look (briefly) at panchromatic film with a dim enough deep green safelight -- because your eyes are more sensitive in that wavelength than the film. But make that green light brighter, or leave it shining on the film too long, and it'll fog the film.

Chan Tran · Nov 17, 2020

For the safelight the limit is for both heat and light intensity. Brighter light of exact same color spectrum still can fog.

pentaxuser · Nov 17, 2020

You can only suck it and see. Try a standard tungsten 25W bulb in it If it gives you enough light and time to do what you need to do in the darkroom then ask yourself if you need to bother with a LED. What you know is that in a Kodak safelight and if the front filter is OK a tungsten bulb is OK

You will of course use more energy with a 25W but given the energy usage in the average house over a year then the saving is very marginal
If you know of an LED bulb that gives a lot more light but is completely safe then isn't this the illusory "something for nothing" which doesn't exist?

pentaxuser

weasel · Nov 17, 2020

pentaxuser, its only something for nothing if the heat is the limiting factor; if I can get a brighter light, assuming it doesnt fog paper, it seems like a win. Now may other question; does the spectrum of the light affect the filtration?

pentaxuser · Nov 17, 2020

weasel said:
pentaxuser, its only something for nothing if the heat is the limiting factor; if I can get a brighter light, assuming it doesnt fog paper, it seems like a win.

Yes I understand but what I was trying to say and apparently failing is that if a certain level of illumination fogs paper then it doesn't matter whether that illumination is tungsten or LED There is nothing about LED light that makes it safer per se

pentaxuser

MattKing · Nov 17, 2020

You may find that a narrow spectrum LED will permit higher light levels, because tungsten bulbs are inherently wide spectrum, and safelight filters aren't necessarily narrow cut.
My 16 foot red LED rope light puts out way more light than any normal (i.e. not Thomas sodium vapour) safelight I have ever worked with.

Donald Qualls · Nov 17, 2020

Well, yes, there is. LED lamps can be very limited in emission range -- some are nearly as monochromatic as a diode or gas laser. Those, if the correct wavelength, can be very safe at rather high brightness, just like the Thomas and Duka low pressure sodium safelights. For instance, if I have LEDs that emit a narrow peak at 640 nm, they can be bright enough to read easily, yet give very long safe times with both graded and multigrade B&W papers.

pbromaghin · Nov 17, 2020

Are you setting up for B&W printing or color? I'm in a pretty similar situation to you and I found a deep-red led indoor grow bulb that emits only between 650 and 750 nanometers. Its safe for all Ilford papers and is really bright. It won't work for anything with red sensitivity, though.

138S · Nov 17, 2020

weasel said:
Can I put a brighter LED in, and if so does the temeprature range of the light matter?

I'd recommend you use a bare red LED bulb, like this one:

This one is dimmable, you may use a dimmer to adjust light level.

Also a RGB bulb may be quite suitable, you may adjust intensity, and you may have white light when wanted,

You may check this interesting video, a safe light may look safe but it may work like pre-flash, having an impact in the print:

mshchem · Nov 17, 2020

Yeah, all the beautiful Kodak safelights done in by Christmas tree lights . I have Thomas safelights that I have picked up used, I even use for color. As Donald says these low pressure sodium lamps have two distinct emission lines that are visible, but paper isn't bothered by within reason. The red LED rope lights sold at Home Depot would be the first thing I would try.
You could put a red LED bulb in your safelight. The thing that stinks about LED lights is they run off DC, the built-in transformer in the Edison socket bulbs can get hot as a griddle.

The bulb manufacturer talks about LEDS lasting forever, problem is the little power supplies built in to the bulb burn out from the on off cycling.

138S · Nov 17, 2020

mshchem said:
The thing that stinks about LED lights is they run off DC

We may use any socket for the led bulb, the safe light box is not necessary, any lamp may do the work.

Lights from SOX Sodium lamps are interesting because the eye may see better with "less light", but LEDs also substitute a low pressure Sodium lamps (SOW) with advantage

RA-4 paper (Fuji Crystal Ar.) has a deep valley in the spectral sensitivity around 600nm:

but we need a very narrow band which SOX sodium porovides but also LEDs do the same at very low price.

High Pressure Sodium SON lamps are not suitable, only Low Pressure SOX ones are good, but LEDs are an smarter solution

UnderwoodPhoto · Nov 18, 2020

Watch out, for some LED bulbs although they produce less heat than incandescent, the heat they do produce can and will destroy themsekves in an enclosed fixture. It only took 4 hours for a 40 watt equivelent 5 watt bulb to become as dim as a night light. And it never recovered. Limit your bulb to 1 or 2 watts and it might survive.

138S · Nov 18, 2020

Yes... thermal factors are always important... for this reason, instead using a white led bulb, it's better to use a Red led bulb so the there is no need to generate the light/heat that will be blocked anyway by the filter, but a red LED bulb it does not require a box at all, we may use a dimmer or we may simply point the light direction more or less to the wall or using any mechanical barrier to get the wanted effective power.

________

To visually inspect the spectrum of the light we may use a Coking A042 filter or the like

or we may use the reflexion on an audio CD

We'll know the truth from a paper fogging test, but the "rainbow" from the light source will give us a clue about how narrow is the emision bandwidth.

pentaxuser · Nov 18, 2020

What isn't clear to me is: Behind a normal filter such as an Ilford 902 will an LED per se that gives a greater illumination that say a 15/25W tungsten white light bulb intensity be safer than its tungsten equivalent . So if for instance a 25W tungsten in a 902 box is the max for a safelight, can you use a white light LED that gives say 40W equivalent illumination and still be safe?

If so what does the LED need to peak at ( 640nm?) and how do you find out which bulbs meet these standards. What is the safe range?

pentaxuser .

138S · Nov 18, 2020

pentaxuser said:
If so what does the LED need to peak at ( 640nm?) and how do you find out which bulbs meet these standards. What is the safe range?

The "power safe range" depends on safe light to paper distance and in the reflexion in the room...

If you have a tungsten safe light and you want to replace the bulb by a white LED one, and wanting to conserve the same emiting Red Light Power, then you should replace the tungnsten bulb by a white LED bulb of around Watt real 15% of the tungsten power, depending on cold vs warm LEDs and efficiency that 15% can be a 10% or a 20%. (A Cold white LED throws a lower Red share and more power is blocked in the Red filter), so to substitute a 25W incandescent bulb you need a 2.5W to 5W while led, but you may also use a 1W or 2W Red LED bulb, there is no need to generate green an blue inside the box to only reheat it.

If you replace a 25W incandescent bulb inside the box by a 7W white LED that is 40w equivalent then you will have an stronger Red light, of course it will be less safe, but the fogging effect wil depend on what amount of that light goes to the paper and for how much time, at the end we increase the red light to see better until we have an effect in the print... If we have too much light we always can use a dimmer to adjust it, this is convenient because when do some kind of job in what the paper is a long time exposed then we may lower the safelight power. We also may mask a bit the safe light with anything opaque, or we may simnply point the light in a less effective direction, of course...

Personally I'm perfecting a LED source for the enlarger including a controller, I've placed a Relay in the design to power off the safe light while the timer is making the exposure, in that situation we don't need the safe light On and I calculated this may decrease the safe light exposure on paper to 1/3 if I'm fast placing the paper on the easel and moving it to the developer tray (shat is properly shaded).

Also I found that painting in the wall behind the enlarger black (or placing a black thing there) is very benefical, photopaper reflects 90% of the light and if the wall area that's just behind the enlarger is also while then a lot of light comes from there.

MattKing · Nov 18, 2020

pentaxuser said:
What isn't clear to me is: Behind a normal filter such as an Ilford 902 will an LED per se that gives a greater illumination that say a 15/25W tungsten white light bulb intensity be safer than its tungsten equivalent . So if for instance a 25W tungsten in a 902 box is the max for a safelight, can you use a white light LED that gives say 40W equivalent illumination and still be safe?

If so what does the LED need to peak at ( 640nm?) and how do you find out which bulbs meet these standards. What is the safe range?

pentaxuser .

The filter is there to block the unwanted wavelengths of light. It isn't perfect - if the installed bulb emits too much green light (as an example) some will get past the filter. That, along with heat concerns, is why there are limits specified for tungsten bulbs.
With tungsten bulbs, the distribution of light is fairly consistent over the spectrum. If you switch bulbs to another with the same rating, there won't be a lot of change.
With LED bulbs, there is more variation between two different bulbs - one may have more green (as an example) than another.
So the "equivalence" numbers aren't particularly reliable when your intent is to only use a small part of the spectrum.
It works much better if the LED bulb you put in already does much of the spectrum limiting for you.
I've had best results from red LED bulbs, but as availability and choice improve, you may find it easier and cheaper than it once was to find an LED bulb that has the narrow spectrum in the amber range that the Ilford 902/Kodak OC filter is designed to provide.

pentaxuser · Nov 18, 2020

MattKing said:
I've had best results from red LED bulbs, but as availability and choice improve, you may find it easier and cheaper than it once was to find an LED bulb that has the narrow spectrum in the amber range that the Ilford 902/Kodak OC filter is designed to provide.

Thanks Matt. My problem here in the U.K. is that there is a vast range of LEDs available and has been for a few years but they are not aimed at the darkroom safelight market which frankly is by any normal standards for the lighting market almost non existent so spectrum and wavelength appears to be near impossible to find via a search engine. Out of interest I did a search a couple of nights ago and wavelength and spectrum just weren't there

N American members who may know what to look for and have found suitable bulbs in the U.S. may not be able to help a lot if at all on stockists other than in N America

pentaxuser

MattKing · Nov 18, 2020

My red LED rope light is aimed at the Christmas market

pbromaghin · Nov 20, 2020

I got a red grow light made to encourage flowering. It should be save for all Ilford papers.

Here is the claimed light distribution (sorry it's so big):

Here's their contact info from their website:
ABI® LED Lighting is a division of JacobsParts Inc.
8227 Northwest Blvd Ste 120
Indianapolis, IN 46278

Email: info@abilights.com
Phone: 800-738-7120

138S · Nov 20, 2020

Yes... ilford new RC V is stated to have this spectral sensitivity:

Anyway always a fogging test has to be made to see the light power that has an impact, of course...

weasel · Nov 21, 2020

Well, to answer part of my own question; I put a 40w equilavent led bulb in my safeight with an oc filter. It hangs about 16 inches down from a ten foot ceiling, and I hung it so it faces up to better spread the light. Passed fogging tests with the paper I have on hand.

138S · Nov 21, 2020

weasel said:
a ten foot ceiling

Just I would remark the distance effect... effective direct power falls proportional to distance2

if 25w were safe at 1m then at 3m a power of 25x32 = 25x9 = 225w would be equally safe !!!

That calculation is not exact if wall are not perfectly black and reflexions play a dominant role, but it shows how important is distance...

RalphLambrecht · Nov 21, 2020

weasel said:
Finally after about ten years im finnaly setting up my permanent darkroom, yeah! I have a couple questions about bulbs for my safelight, and my enlarger that I have been unable to find concrete informatiion for.
My safelight is a standard kodak model D. It is listed as taking a 25 watt bulb max. My question is, is that because of the light level, or the heat level? Can I put a brighter LED in, and if so does the temeprature range of the light matter?
Same question for my leitz focomat 1c. If I want to put an led in it, will the temperature range of the bulb affect multigrade filters, and if so, what temperature range should the bulb be?

as long as you use 'warm-white' you should be OK as far as wavelengths and filtration go but, the increased brightness alone demands a new safelight test

138S · Nov 21, 2020

Better explained, impossible...

a couple questions about light bulbs

weasel

Donald Qualls

Chan Tran

pentaxuser

weasel

pentaxuser

MattKing

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Donald Qualls

pbromaghin

138S

mshchem

138S

UnderwoodPhoto

138S

pentaxuser

138S

MattKing

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pentaxuser

MattKing

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pbromaghin

138S

weasel

138S

RalphLambrecht

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a couple questions about light bulbs

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