Tritium Backlit LCDs

[abem]

Greetings,

I recently got an inexpensive, but nice Fairchild LCD watch (NOS, around $25 with box etc), made around 1977. Even thought the half life of Tritium is only about 12 years, almost 3 half lives after this watch was made the display still glows faintly. It must have been something when it was 10 or 20 times brighter.

It appears to the eye a very pale green, much like a phosphorescent substance. The phosphor activated by the Tritium beta radiation is probably very similar to that found in "glow in the dark" materials although it doesn't seem to be activated by light - anyone know the answer to this? It's too faint to be able to read the time by, but it shows nicely in a long-ish exposure (~30 seconds) photograph. It sure would have been neat to see one of these when they were new!



-abe.

[Handy]

It may be worth seeing whether you can get it re-lumed with Superluminova. It'll glow like a torch then.
Cheers,
Ian

[rewolf]

I have the very same watch, with its backlight at the same level: very faint, just visible in darkness, but not enough to read time.
The tritium phosphor is encapsuled in two flat glass tubes which sit under the semi-transparent silverish reflector underneath the LCD. On your photo it appears that the lower of these tubes is still brighter than the other.
I too noticed that the phosphor is NOT activated by light, but I don't know anything more about it.

Here's an old discussion about Tritium backlight: http://dwf.nu/viewtopic.php?t=1546&highlight=tritium

[abem]

Correction: The phosphor IS activated by light. The effect is slight enough that I missed it at first, but it is most definitely there.

-abe.

[LEDluvr]

Abe, if you could get that watch re-lumed it would be quite a feat!
I don't doubt you are looking into it as I type this message.....

[morelite]

A UV light will activate the phosphor but only while present, it will not charge it like normal lume.

If you can get to the tritium vials (tubes) and measure them I may have some that will replace them.
I have some new flat tubes that are 20mm x 2.5mm x .75mm in green and orange.

[morelite]

[rewolf]

A UV light will activate the phosphor but only while present, it will not charge it like normal lume.

If you can get to the tritium vials (tubes) and measure them I may have some that will replace them.
I have some new flat tubes that are 20mm x 2.5mm x .75mm in green and orange.

Sounds very interesting! Today is "new battery day" for some of my watches, the Fairchild is among them, so maybe I can tell you tomorrow.

[abem]

Yes, I certainly did look into it...

Danger, warning!... do not do what I did. The old mantra about feline curiosity comes to mind. Here is the result:
http://www.dwf.nu/viewtopic.php?t=3945

-abe.

[rewolf]

Oh sh..

I didn't change batteries yesterday (got better offers for the evening ), but will some time this week.

[clockace]

tritium is a radioactive isotope. it does not need exposure to light to activate. the reason it is sealed in the glass tubes is because there is a danger to ones health if it is ingested, either by inhaling or other means. it is for this very reason that watch hands are no longer radium. same problem, radioactive. i would be very careful with these. peter

[LEDluvr]

it is for this very reason that watch hands are no longer radium. same problem, radioactive

Yes, but I sure miss those radium dial watches. The kind that glowed even in the middle of the day! Surely it wasn't enough readium in those old-time watch faces to give you wrist cancer? The workers applying the radium paint, well... that's another story.

[charger105]

Looks like someone has hijacked your image Abe:

http://cgi.ebay.com.au/Vintage-Fairchil ... 2a07b7d919

Rgds.

[rewolf]

If you can get to the tritium vials (tubes) and measure them I may have some that will replace them.
I have some new flat tubes that are 20mm x 2.5mm x .75mm in green and orange.

2 vials, 18mm x 3.4mm x <1mm each.
20mm length would just fit, but not in the original vial holder. I'll post some photos later.

[abem]

Note: The person who hijacked this image did so with my permission. She's the seller who I bought my watch from. I sent her a set of photos because she was trying to sell these watches using some murky indistinct images and not having any luck. I had some decent images available, so I thought I'd help her out a bit.

-abe.

[J Thomas]

[LEDluvr]

Yes, that was mighty kind of you Abe. But aren't you interested in buying the watch yourself for the replacement module?

[rewolf]

If you can get to the tritium vials (tubes) and measure them I may have some that will replace them.
I have some new flat tubes that are 20mm x 2.5mm x .75mm in green and orange.

2 vials, 18mm x 3.4mm x ~1mm each.
20mm length would just fit, but not in the original vial holder. I'll post some photos later.

Click images for full size:


The LCD is direct driven (not multiplexed), 39 segments + 1 common.
Note the two extra segments between the seconds digits - they are used for the nice DOW display (M,Tu,W,Th,Fr,Sa,Su).


The "glow" photo was made with 15s exposure time @ F2.8 and a rather poor camera.

[morelite]

After seeing that vial holder tray I think it may be better and easier to fill it with Glow Inc's glow powder mixed into clear epoxy.

[abem]

Hmmm, this is promising...

The tray holding the vials is 20mm wide, so clearly the vials will need to be 18mm or so to fit in the little tray:


However, the little tray seems completely optional. It fits neatly in a little space in the module behind the display. So, it seems that the 20mm vials could be placed in that space minus the tray with no problem:


How much do the 20mm tritium vials cost?

-abe.

[morelite]

These two people sell them.
http://www.cpfmarketplace.com/mp/showth ... ht=tritium

http://www.cpfmarketplace.com/mp/showth ... ht=tritium

I bought them from one of them, can't remember which one I got the flat vials from because neither have that size listed right now and I've bought different sizes and shapes from each them over the years.

IIRC they were around $12 or $13 each.

I wouldn't choose any color other than green for backlighting, the other colors are cool but not near as bright. Even the flat green vials are much dimmer than the round vials because they are so thin and don't contain as much tritium.

[morelite]

The tray may not be needed but it might be helping reflect or direct all the glow toward the LCD.

Does it look like thicker vials could be used? The round vials are much brighter and easier to get. They are smaller but we could install more of them.