LED bulb in safelight

mauro35

Member
Joined
May 28, 2013
Messages
219
Location
Finland
Format
35mm
Dear APUGers,

I have a technical question. I was thinking of using an LED bulb instead of a regular incandescent 15W bulb in my safelight with OC filter for black and white printing. The reason being that LED bulbs are nowadays very affordable here in Europe and I particularly like that they run cold and last practically for decades. I could get a 1.8W LED bulb, equivalent to about 10W incandescent, with a color temperature of 2700K, but I am not sure whether the difference in emission spectrum will affect the filter and/or create spikes at specific frequencies that can leak out fogging the paper. Has anybody tried something similar or does anybody know more specifically how LEDs differ from regular bulbs?

Thank you all!

Mauro
 

Paul Howell

Subscriber
Joined
Dec 23, 2004
Messages
9,582
Location
Scottsdale Az
Format
Multi Format
Good question, I have thinking about pulling in amber colored LED in may small safelight with an OC filter and a red compact fluorescent light bulb in my larger safelight with a dark red filter, I use a standard red bulb but CFL will be cooler.
 

M Carter

Member
Joined
Jan 23, 2013
Messages
2,147
Location
Dallas, TX
Format
Medium Format
I use a red "party" spiral CFL in a clip-light and had no fogging trouble - until I got some of Freestyle's cheap "student" RC paper (usually use Ilford RC for tests and setup and contact strips). The Freestyle stuff fogged like mad. I taped some red lighting gel over the fixture to be safe.

I have several now and my darkroom is very bright red, I really love it. No fogging, even with my stash of vintage-ey Lith papers.

If the lamp is cheap enough to take a chance, buy it and test?
 

Ken Nadvornick

Member
Joined
Mar 18, 2005
Messages
4,942
Location
Monroe, WA, USA
Format
Multi Format

If you can get an LED bulb to pre-test, install it into your safelight as you would a normal incandescent bulb. Then turn it on and examine the emitted light as it reflects from the surface of a common CD or DVD recorded disc. The disc will break the reflected light up into narrow bands of discreet colors. Make certain the room is truly dark with no other sources of light.

Look for any blue or green bands or spikes. Look carefully, as these can often be very faint. If you see any, the bulb will not work for your intended purpose. If you don't see any, then follow up with a proper pre-flashed paper fog test to confirm your observations.

You can use the same technique to view normal sunlight, a normal incandescent bulb, and the unfiltered LED bulb to contrast the differences between those various emitting sources. This can be an interesting exercise all by itself.

Ken
 
OP
OP

mauro35

Member
Joined
May 28, 2013
Messages
219
Location
Finland
Format
35mm
Thank you for the replies. The test of light reflected from the surface of a CD is a great idea! I didn´t think about it. I am going to do just that! Appreciating your help.

Mauro
 

john_s

Subscriber
Joined
Nov 19, 2002
Messages
2,135
Location
Melbourne, A
Format
Medium Format
When I was in school a long time ago, in physics class we used a little device through which you could view the spectral breakdown of a light source. The most dramatic were the yellow sodium vapour and cool white mercury vapour lights: their light was clearly bands of single wavelengths. I'm wondering if this sort of thing is findable now. Ken's suggestion above revealed to me the reason why my orange LEDs fogged paper. Now I use very red LEDs, not as nice to work under, but sure is safe for paper!
 

bdial

Subscriber
Joined
Jan 2, 2005
Messages
7,450
Location
North East U.S.
Format
Multi Format
If you will be using a white LED through the OC filter, you probably won't need to worry about spikes much, because the filter should take any out. That spectrum test with a CD is more relevant to situations where you are illuminating directly from the LED, for example, a red one.

OTH, you may not get much light, because the LED spectrum is so uneven, the filter may take out most of the what the LED produces.
Let us know how it turns out.
 

kb3lms

Member
Joined
Jun 24, 2006
Messages
1,004
Location
Reading, PA
Format
35mm
The 15w incandescent in one of my safelights with OC filter burned out. I couldn't find another at the local store but they did have yellow LED party type bulbs that are basically the same size. Installed one of those with the OC filter and it works great and runs cool. They also had red LED bulbs of the same type and they also seem to work quite well, just as the bare bulb.
 

Ken Nadvornick

Member
Joined
Mar 18, 2005
Messages
4,942
Location
Monroe, WA, USA
Format
Multi Format

Was it a diffraction grating?

Ken
 

MattKing

Moderator
Moderator
Joined
Apr 24, 2005
Messages
52,419
Location
Delta, BC Canada
Format
Medium Format

mesantacruz

Member
Joined
Feb 21, 2013
Messages
256
Format
Medium Format
there's a thread i started about something similar.

http://www.apug.org/forums/forum43/119448-best-safelight-99-99-safe.html

I'm still using this safelight. Make sure you order from somewhere that gives you the wavelength reach and that is out of reach of what your paper is affected by. I believe this is a better approach than actually buying a white led and trying to cut the bandwidth that way.

BTW, these less are so bright it makes a world of difference!
 
OP
OP

mauro35

Member
Joined
May 28, 2013
Messages
219
Location
Finland
Format
35mm
bdial said:
OTH, you may not get much light, because the LED spectrum is so uneven, the filter may take out most of the what the LED produces.
Let us know how it turns out.
Click to expand...

I did the safelight test with the surface of a CD. I tried both LED bulb and incandescent. They look identical to me, concerning the color of light transmitted by the filter. As bdial suggested, there is some reduction in light intensity with the LED, but I was able to still see quite clearly in the darkroom, so it might be good. Hope to be able to test for paper fogging soon.
 

youngrichard

Member
Joined
Jul 13, 2007
Messages
153
Location
London, Engl
Format
35mm
I put mains voltage LEDs , orange or yellow from Maplins (UK electronic chain) (had to get GU10 or whatever GU number the fitting is) adaptors. See picture. Put them in my Beehive safelights with OC safelights; they are a bit directional so you see the light is brighter in the centre of the safelight glass, but they work a treat, and satisfy my fogging tests.
Richard
 

Attachments

  • DSC_0289.jpg
    255.2 KB · Views: 209

Rich Ullsmith

Member
Joined
Jan 26, 2007
Messages
1,159
Format
Medium Format
I made a safelight from component leds, the data sheet depicted a very sharp peak at 660nm which still fogged rc paper (probably developer incorporated) at 15 minutes with the coin test.

I have tried the CD reflective experiment and honestly cannot tell if other bands are produced, but I imagine a prism would be much more illustrative.

In any event, 660nm should be safe for any paper but I tested it and it is not. Problem solved by bouncing off the ceiling. I also tried 635nm bulbs which also fogged unless bounced off the ceiling.

By tinkering with light placement you can get a room pretty bright with red LED's, cheaply too.
 

Rich Ullsmith

Member
Joined
Jan 26, 2007
Messages
1,159
Format
Medium Format
Barzune, those are the 635nm bulbs that fog my rc paper unless reflected.
 

GKC

Member
Joined
Dec 12, 2012
Messages
222
Location
Fresno, wher
Format
Large Format
I use a string of red led Christmas lights I bought at the end of season close-out at the local CVS. No fogging to report and it gives my inner sanctum a downright jolly, festive atmosphere
 
OP
OP

mauro35

Member
Joined
May 28, 2013
Messages
219
Location
Finland
Format
35mm
Just to report quickly on my experience, at last I had opportunity to print and I used my new LED lamp in the safelight. No problem at all with fogging, although I did not have time to run a full extensive test. I can say no fogging is apparent within normal RC paper handling time (4-6 min.). But the reduced light intensity compared to a 15W incandescent made me a bit tired in the long run. It might be that this is not the best solution for long sessions.
 

Artful Dodger

Member
Joined
Aug 26, 2015
Messages
4
Location
South Coast
Format
35mm
It might be handy to know there are several different types of LED bulb on the market which can sometimes be very confusing.

  1. I bought one red mains LED bulb that was a white LED bulb with red pigment painted on it. This would be a terrible choice for a darkroom safelight without further filtration as it let lots of white light out as well as red.
  2. Some coloured LEDs are actualy blue-ultra violet LEDs with a coloured phosphor that changes the frequency of the emitted light. This would also be a problematic choice since much of the blue-ultra violet still leaks out. This will fog paper.
  3. Some LEDs directly produce a narrow band of red or amber light without also producing blue-ultra violet or white light. My experience is these can work perfectly as a safe light but I have not yet found any mains powered versions.
I use a 1 watt led that I use as a safe light
http://www.rapidonline.com Order Code: 55-2243
It's seriously cheep to buy at £1.61 which is aprox $2.50
There must be plenty of other retailers that stock such bulbs
I run this LED from a six volt battery pack in series with a 47 ohm 1 Watt resistor (cost £0.13 or $0.20) which gives me considerably less than 1 watt of power (170 mW aprox). A six volt dc transformer would also work OK but this would be very slightly more complicated. It is important to regulate the current (eg by using a series resistor) when using such an LED because directly connecting them to a battery or constant voltage supply normally causes them to explode.

I sit my LED on a shelf pointing up at a white painted ceiling. This gives ample light I which I can easily read data sheets and labels by.

To be really safe you could run such a 1 Watt led inside a traditional safe light filter. Since the LED is very efficient and gives out a frequency of light that the filter passes it will probably still be as bright as a normally lit safe light but run much cooler.
As previously mentioned using a diffraction grating or the reflection from a CD is good advice. When tested this way my LED gives out some orange light and a tiny amount of yellow. If you can see any green or blue light in this test you will need either a different LED or additional filtering.
 
You must log in or register to reply here.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…