Homebuilt sodium safelight?

MattKing · Sep 25, 2020

If your goal is a safelight for black and white, I've just re-tested my 16 foot red LED rope-light in my new bathroom/darkroom after our move, and it still passes the Kodak Safelight test.
When installed near the meeting of the wall and the ceiling, the illumination level rivals a Thomas, the light distribution is far superior to the Thomas and you can power it using the safelight outlet on many timers. It is also cool and uses very little electricity.
The festive glow from it is a bonus! And in normal years, availability would be ramping up nicely (it is mainly marketed for Christmas use).
I wish they made it with the right spectral emission for RA-4.

Donald Qualls · Sep 25, 2020

I'm much better with a soldering iron, razor saw, and glue than I am with sheet metal tools anyway (been a model airplane builder a couple times, and I've built some ham radio stuff from kits fairly recently). Suitable yellow LEDs are under a buck each, I've got a large surplus of little wall wart power supplies, and I know how to use a multimeter.

@MattKing Yes, safelight for multigrade is trivial -- I've got one already, a 15W red coated bulb in a reflector clamp lamp, used previously in my old darkroom, that I can direct at the (white, textured) ceiling and light at least half of my darkroom quite adequately. It's the RA-4 I'm trying to set up, and with no ability to even buy LPS other than replacement bulbs or actual Thomas safelights (which seem high just to get the electrics), not to mention the ten minute warm-up, I'm pivoting back to yellow LEDs (narrow emission between 475 and 500 nm, knowing they might still need filters).

htmlguru4242 · Dec 30, 2023

Digging up an ancient post here, but I've got a few Low Pressure Sodium (LPS/SOX) lamps, if Donald (or anyone else) is interested in one.

Also, the high-power amber LEDs that are available from LEDSupply and others are around the same wavelength as a SOX lamp (just under 600nm), and are less than $20 for a board that puts out a couple hundred lumens, which is more than enough.

kykr · Dec 31, 2023

Another thought on LPS, I came across it for two situations. One was that a place was becoming a “hangout” for unwelcome guests for late night parties. LPS makes everything monochromatic orange and black so it looks terrible in a normal situation. The parties quickly found other more inviting places…

The other is astronomical observatories. I didn’t read all the posts here but even 20 years ago there weren’t many companies making LPS fixtures, especially compared to normal outdoor and roadway lighting. Today anything out there is probably old inventory. If you have a nearby observatory, maybe see what they’re using these days as another option.

However, the two I’ve seen near me have typical white LED. Another advantage of LED is that you can turn it on and off (and back on) instantly. It’s also easy to dim most fixtures. I don’t know what either does when they’re using telescopes. With LPS, it’s going to need to stay on until you’re done. One more idea, some coastal areas require “turtle safe” amber lighting. That may be similar as well.

rcphoto · Dec 31, 2023

Donald Qualls said:
I'm much better with a soldering iron, razor saw, and glue than I am with sheet metal tools anyway (been a model airplane builder a couple times, and I've built some ham radio stuff from kits fairly recently). Suitable yellow LEDs are under a buck each, I've got a large surplus of little wall wart power supplies, and I know how to use a multimeter.

@MattKing Yes, safelight for multigrade is trivial -- I've got one already, a 15W red coated bulb in a reflector clamp lamp, used previously in my old darkroom, that I can direct at the (white, textured) ceiling and light at least half of my darkroom quite adequately. It's the RA-4 I'm trying to set up, and with no ability to even buy LPS other than replacement bulbs or actual Thomas safelights (which seem high just to get the electrics), not to mention the ten minute warm-up, I'm pivoting back to yellow LEDs (narrow emission between 475 and 500 nm, knowing they might still need filters).

Lots of cheap thomas safelights on ebay right now.

BobUK · Dec 31, 2023

You may have already found the article on Youtube to make your own replacement filters for the Thomas Safelight.
If not, try searching for The Naked Photographer, and then search his Youtube channel for
DIY Safelight Filters for the Thomas Duplex

He gives the combination of filter gels to make replacements for the Thomas.

I won't put a link here as quite often they do not seem to work. Just have a search for the above.

Good Luck with the project.

eli griggs · Jan 1, 2024

I bought my
Thomas Safe Light filters from a local Barbizon lighting company and they have small swatch books on their filters. https://barbizon.com/

My experience is with the full sheet gels, from which several Thomas gel sets can be cut.

Two different gels needed

Donald Qualls · Jan 2, 2024

rcphoto said:
Lots of cheap thomas safelights on ebay right now.

Downside of a used Thomas is that you don't know the remaining life of the sodium bulb(s), and replacements are pretty much unobtainium these days. Literally no one appears to be manufacturing low pressure sodium lamps in any form factor these days (no demand, with LED pushing out high pressure sodium from area lighting and HPNa already having replaced LPNa), and I don't know anything about their shelf storability -- will a bulb manufactured in 1995 and never powered up have the service life of a newly manufactured one? I'm not sure anyone really knows.

Narrow-band LED at about 585-590 nm seems like a better starting point if you don't already have a Thomas. Plus, LED is dimmable with a fairly simple chopper circuit (a dual 555 chip, a driver transistor, and a few discrete components -- I'm not an electronics guy and I'm pretty sure I could find the parameters needed to build an LED chopper).

koraks · Jan 2, 2024

Donald Qualls said:
LED is dimmable with a fairly simple chopper circuit (a dual 555 chip

'Choppers' are something from the 1950s when they used mechanical means to convert DC into AC.
The 555 is still an option, but I don't think anyone would design a circuit around one these days; I did it a couple of months ago for the sake of it, but realistically, you'd just get any off-the-shelf LED driver that accepts a PWM input and then use a simple microcontroller (or an Arduino board) to generate the desired duty cycle PWM. From there, anything can hooked up to it in terms of control logic/interfaces etc. Here's what I did in my present darkroom: https://tinker.koraks.nl/photography/some-light-to-the-darkroom/
And yes, it also has 595nm orange LEDs for color work - or at least that's what I wanted to experiment with. Which I did, and then quickly concluded that today's color paper really isn't made for safelight use, which is also indicated quite clearly in the datasheet. The 595nm wavelength may work for many B&W papers, but frankly I've never tried it because I use deep red for that.

Donald Qualls · Jan 2, 2024

I did mention I'm not an electronics guy.

"Chopper circuit" is what I've heard for years to refer to anything that just "chops" up the DC into square wave pulses, usually PWM for speed control. And a 555 is what I automatically think of in terms of IC timer/square wave circuits because cheap and easy to control. Arduino (never mind a dedicated microcontroller) and associated assembler-source software is more foreign to me than IC electronics -- it would never occur to me to use something like that for a simple DC light dimmer circuit. Part count (it seems) would be higher than a 555/driver circuit, and it would cost more to build (especially if you don't already have an Arduino/etc. hobby). Last I checked (a couple years ago), 555-derived ICs were still readily available, and custom PCBs are fairly cheap -- cheap enough it's not really worth sourcing the equipment and chemicals to make your own.

koraks · Jan 2, 2024

Donald Qualls said:
"Chopper circuit" is what I've heard for years to refer to anything that just "chops" up the DC into square wave pulses

Yeah, they used to be called that and the name seems to have stuck. Strictly speaking, a chopper is really the sort of mechanically-driven switch I mentioned. You could get them in neat little metal cases with an octal base, like the ones used also beam tetrode tubes (e.g. 6CA7/EL34). They were superseded by purely electronic oscillators, and today it's all PWM. Conceptually, it's still 'chopping up DC', of course.

Yes, 555's are easily available, also in SMD format. And sure enough, one could make a PWM dimmer for an LED with them. It's fairly straightforward, and indeed quite cheap. The parts count would end up similar to a small uC circuit, cost as well. The microcontroller circuit will be way more flexible and it'll be more stable/accurate, since the stability of the 555 circuit will depend on the passives and temperature. For a simple darkroom safelight, this will not matter much.

Donald Qualls said:
custom PCBs are fairly cheap -- cheap enough it's not really worth sourcing the equipment and chemicals to make your own.

Depends a bit; the turnaround is too long to my taste. And it's kind of fun being able to DIY.
A bit like photography; I could get a better shot much of the time with my Samsung phone than with my EOS 35mm camera, but where's the fun in that?

There are many ways to skin a cat, as they say.

Donald Qualls · Jan 2, 2024

koraks said:
There are many ways to skin a cat, as they say.

To which I usually reply: Cats hate that expression.

There are always multiple ways to solve a given problem. For me, it's conceptually simpler (even if less stable and versatile) to use simple 1970s tech than something that didn't even exist last time I had an electronics related class. And surface mount is evil, to me -- I lack both the equipment and skill to solder SMD; I'll continue to use through-hole boards and lead wire/DIP package components if available. They'll probably still be around until after I'm likely to want to build anything new...

gdavisloop · Oct 19, 2024

A bit late to this thread, but I also had the Thomas safelight decades ago but it seems it was thrown out. I was interested in LPS light and wanted to recreate that several years ago. I found it wasn't too difficult to get a 35W Philips bulb, but the original ballast was much harder. On a tip, I tried a modern 35W solid-state fluorescent light ballast and that worked perfectly!

The socket does not actually support the bulb so I decided to just solder the ballast directly to the pins. I put the bulb inside a clear plastic 12" pencil box. I put aluminum foil behind it as a reflector which didn't really work because the shape has no accuracy.

I don't have any idea what to do about the Thomas filters, as I was just interested in the light - not the safelight.

I used this ballast from Amazon: Fulham Lighting WH2-120-C. The bulb was from eBay.
--Gary

mshchem · Oct 20, 2024

gdavisloop said:
A bit late to this thread, but I also had the Thomas safelight decades ago but it seems it was thrown out. I was interested in LPS light and wanted to recreate that several years ago. I found it wasn't too difficult to get a 35W Philips bulb, but the original ballast was much harder. On a tip, I tried a modern 35W solid-state fluorescent light ballast and that worked perfectly!

The socket does not actually support the bulb so I decided to just solder the ballast directly to the pins. I put the bulb inside a clear plastic 12" pencil box. I put aluminum foil behind it as a reflector which didn't really work because the shape has no accuracy.

I don't have any idea what to do about the Thomas filters, as I was just interested in the light - not the safelight.

I used this ballast from Amazon: Fulham Lighting WH2-120-C. The bulb was from eBay.
--Gary

View attachment 381336

Neat! I loved sodium vapor streetlights. The LEDs that have been plastered all over our neighborhood are ridiculously bright and white. We live next to a bit of wild land. At night there's a streetlight nearly a mile away so brilliant it could be used for a football match.

MTGseattle · Oct 20, 2024

Here's what may seem like a wacky thought to add;

what about adding the appropriate Roscoe gel sheet/s to the inside of one of the porta-trace light tables? these should be fairly inexpensive used, decent low-profile housing and circuitry already handled. one may have to source some simple brackets and pop-rivets or other hardware, but I think many of us who tinker likely have that stuff sitting around already. The other addition I can think of would likely be an extension cord with a built-in switch unless one wants to re-wire the assembly also.

MTGseattle · Oct 25, 2024

I realize my idea above bypasses the "Sodium" aspect of the thread.

eli griggs · Oct 26, 2024

MTGseattle said:
Here's what may seem like a wacky thought to add;

what about adding the appropriate Roscoe gel sheet/s to the inside of one of the porta-trace light tables? these should be fairly inexpensive used, decent low-profile housing and circuitry already handled. one may have to source some simple brackets and pop-rivets or other hardware, but I think many of us who tinker likely have that stuff sitting around already. The other addition I can think of would likely be an extension cord with a built-in switch unless one wants to re-wire the assembly also.

Thomas safe light replacement "gel filters" sourced from, "Barbizon Lighting Company", here in Charlotte, NC., or elsewhere, are what I use, a combination of two hours, are inexpensive, with plenty of material, enough for a full second set.

Homebuilt sodium safelight?

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