DarkroomSource Safelights

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Darkroom Furniture: Safe light

Design
Making a 'can' style safelight
Materials
Tools
Construction
Assembly
Testing a safelight
Testing to see if the room is light tight

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Design

There are several options here, and you need to take into account many different things.

If you paint your room white, you can reflect the light off of the ceiling for more even illumination
You can use a 'can' style safelight which you have either purchased or made
Your safelight might screw into a light socket, like the big red bulbs you can buy
You might want a spot safelight directed at a specific area with higher intensity
depending on the size of your darkroom, you might have one central safelight, one on each side, or more that one on each side

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Making a 'can' style safelight

I don't recommend this if you are not extremely comfortable working with electrical wiring!

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Materials

15 watt light bulb
Light socket, it doesn't matter if it has a switch, you won't be using the switch, but it does need to be the kind that goes on a lamp, so that it has a threaded tail piece. You also need the nut that goes on this piece. The fixture is either permanently attached to, or screws on to a hollow threaded rod. The wires will run through the center of this rod, and nuts on the rod will hold it in place on the bottom of the tin can.
Wire cord with plug - 3' to 6' long
Tin can, big enough for the light bulb to fit into easily when it is screwed into the socket (I used a coffee can)
Kodak Wratten filter OC, round, of a diameter to match your can diameter plus about 1/2"
2 Bolts, 1/4" diameter, about 3/4" long.
2 Wing-nuts to fit the bolts
2 non-locking washers to fit the bolts
2 lock-washers to fit the bolts.
4 bolts, 1/8" diameter about 1/4" or more long
4 nuts to fit the bolts
4 lock-washers to fit the bolts
Strip of metal, 1/4" wide, 1/16" or 1/8" thick, and about 6" long
another strip of metal, 1" wide, 1/8" thick. To figure the length (approximate only) add the diameter, plus twice the length, of the can.
1 can of barbecue spray paint, I used black, but any color will do.
3/16" foam weather-strip, long enough to make the circumference of the can.
Duct tape (it'll fix anything!)

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Tools

Drill and bits, 1/8", 1/4" and one the size of the threaded tail on the light socket
Center punch
Can opener, if your can has not been opened yet!
Tin snips (you can cut the metal with a hacksaw)
Plyers
Metal vise (preferable, you can do it with a couple pair of pliers if you need to)

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Construction

Remove the top of the can, empty the contents, clean out the can (ha ha, want to see more sick humor?)
Use a file to smooth the rough edges where the can opener cut the can, these edges will not be visible, but when you change the light bulb you'll be glad you did this step.
In the bottom of the can, in the center, make a small indentation with the center punch. (Whenever you drill into metal, you want to use a center punch first, so the drill will not slide all over the place)
Drill a hole in the center of the bottom of the can, large enough to allow the tail piece from the light fixture to fit through, but small enough to allow the nuts that fit over the threads to hold the fixture in place. Don't install the light fixture yet.
Drill four 1/8" diameter holes in the side of the can (use the center punch), each about 3/8" from the top (open end), and equally spaced around the edge (90 degree spacing).
Drill two 1/4" holes in the side of the can, 180 degrees from each other (directly across), about 1/3 of the way from the top to the bottom (closer to the top). It doesn't matter where they are in relation to the 4 1/8" holes, don't sweat it.
Drill a 1/4" hole about 1/2" from each end of the 1" strip of metal (2 holes total)
Drill a 1/4" hole in the center of the 1" strip of metal (this will be used to attach the safelight to wherever you put it.
Bend the 1" strip of metal into a square U shape. The center of the U will be the diameter of the tin can, the sides will both be the same length (whatever is left). To find the bend marks, subtract the diameter of the can from the length of the 1" strip and divide by 2. This is the distance from each end that the bends should be made.
Determine the length of each of the 1/4" wide metal filter holders. The equation for this is not pretty:
- A = distance from 1/8" holes in the side of the can to the top of the can (supposed to be about 3/8")
- B = diameter of the filter
- C = diameter of the tin can
- D = thickness of the filter
- L = length to make the 1/4" strips
- L = ( ( B - C ) / 2 ) + A + D + 3/8"
Do NOT cut these to length yet, it is much easier to drill the holes into a 6" piece of metal than into 1" pieces of metal. Do mark the lengths onto the metal.
Drill 1/8" holes into the 1/4" strip, starting 1/8" from one end, and making the next three holes L distance from the previous one.
Cut the 1/4" strip into smaller pieces, with each one now having a 1/8" hold at one end.
Bend the 1/4" strips into a what can best be described as a ? (question mark)
1. the first bend is done so that when the 1/4" strip (filter holder) has it's hole over the hole in the side of the can, the top of the bend will be even with the top of the can.
2. the next bend is done at a distance from the first bend 1/2 the difference between the filter diameter and the can diameter.
3. the next bend is for the thickness of the filter
Bend all four pieces the same.

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Assembly

Attach the threaded rod to the light fixture, if it is not already attached.
Thread the wire cord through the two threaded rod nuts, then the hole in the bottom of the can, then through the threaded rod, tie an overhand knot in the wires, so they can not be pulled back through the rod (make sure you still have enough wire to attach to the light fixture), and attach the wires to the light fixture. Put in a light bulb and test the wiring.
Put one nut onto the threaded rod, push the rod through the hole, up to the nut, put the other not onto the rod, and tighten.
Check the wiring, make sure nothing is frayed, and no bare wires are touching the can.
Insert the 1/4" bolts, from the inside of the can, through both the can and the U bracket, and put on the wing nuts.
Put the 1/8" bolts into the holes for the filter holders, from the inside, and tape them in place with some duct tape. Put three of the filter holders over the bolts, and secure with nuts. FINGER TIGHTEN ONLY.
Slide the filter into place and install the last filter holder
The foam can be used, if necessary to stop light from getting out around the edges, by attaching it to the edge of the can, and then the filter will press against it, or you can use duct tape wrapped around the edges of the filter and the can, in which case you needn't make the filter holder pieces at all - your choice.
Screw or bolt the safelight in place
Plug it in

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Testing a safelight

There are several methods proposed by many different people, I am very conservative with my test, and here is how I do it.

Focus the enlarger, with no negative
Put a piece of paper in the enlarger easel
Cover all but a 3/4" strip of the paper with piece of opaque material
Expose for 1 second
Uncover another 3/4" and expose for another 1 second.
Repeat the uncover and expose until there is only 1 strip left unexposed
Place an opaque object across the paper so that it will cross all the exposure zones created above (a pencil or wood ruler for example)
Let this set in the glow of the safe light for 10 minutes (if you have more than one safe light in the room, turn them all on)
Develop and fix the print fully, wash briefly.
In very good light, look at the print, you should see columns of changing levels of gray on the paper, if there is any indication of the opaque object on the paper, your safelight is not totally safe, or you have a room light leak, or you opened the door during the test.
Note: There is one part of the paper that is never exposed to any light, this is the junction between the last strip, which received no exposure from the enlarger, and the long opaque object, that kept room light from hitting the paper. If this part of the print is not pure white, then you have a problem with either paper pre-fog or over development in the print, or over concentration in the print developer.

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Testing to see if the room is light tight

Recently, in a newsgroup, some one was asking about paper fog, and it occured to me that you could get fog not just from the safelight. So here is another test, this for more general fogging.

Turn out all the lights. Count to 300 (1 one thousand, 2 one thousand, etc) to reach 5 minutes.
Hold your hand about a foot away from your face. Can you see your hand? or an outline of your hand? If you can then you are allowing too much light into your darkroom.
Remove a sheet of paper from the packet. Place it on the enlarger easel. Put a key on it. Count to 300.
Turn the safelight on. Put a coin on the paper. (don't move the key) Count to 300 again.
Develop and fix the print fully, wash briefly.
In very good light, look at the print, if you can see the coin, your safelight is not safe. If you can see the key, then your room is not safe.

Kodak's safelight test procedure.

Visitor Comments

The comments stated below are not necessarily the opinions of Andy Hughes or DarkroomSource

You should sensitize the paper before making the light test. Give it a blast from your enlarger just enough to give it a very slight gray. Then make the test with the keys and coin. I would then keep it three minutes at the enlarger position, three-five more minutes at the developer tray position. (Light might be significantly different there)

Contributed by on 2001-11-12 00:00:00

As I am building up my darkroom as economically (note, I did not say cheaply) as possible, I found a safelight that you can get at any hardware store. While the particular price, brand and model may differ, I got mine for 1/4 what the photo store sells them for.

Value-Bright utility bulb, Red ROJO (model) ($1.89)

I tested it and it works great, at least on Ilford multigrade deluxe.

Contributed by on 2001-12-10 00:00:00

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