Today we were replacing the standard 120 volt incadescent bulbs in some exit signs with LED bulbs. The new LED bulbs wouldn't work, so we went through the typical tests and found a heat-shrinked "splice" that wasn't passing power to the 2 sockets. We cut the splice off and connected the line wire to the 2 socket wires and the new bulbs worked.

What we thought was just a splice contained a diode soldered in line. I've never seen this before. Has anyone else ever seen this and can you explain the purpose of this diode?

Diodes are usually put in line to keep the voltage from flowing in the wrong direction, or to keep it flowing in the right direction (DC). You sure it wasn't a resistor (to limit current)?. If it was a resistor, you can expect the led lamps to blow pretty soon with that resistor out of the circuit.

Are the exit signs rated for the supply voltage you are using on this application? If not, would explain why the part was making the exit sign not work.

Good Luck!

They use diodes to make bulbs last longer. You only get half the wave (without the heat you would get with a resistor). If you had just turned this around your LED light would have worked OK.

It was definitely a diode, Zapped. Extended bulb life is the only thing we could come up with, Greg, but none of us had seen this done before. It was easier to just remove the diode altogether rather than reversing it.

Seems kind of funny to install a Diode in front of other Diodes (the LEDs);)

I am just poking fun here!

Scott

That is an old trick. Those buttons you dropped in an Edison socket that they used to sell to extend bulb life were diodes. Logic would say they reduce brightness by half but it actually works out a little better than that but it does seem to make the bulbs last longer. I have heard theories that it is the DC aspect but nobody has convinced me.
In the case of LEDs it would have virtually no effect if you had it forward biased along with the LED. You would have another .7 voltage drop but that is pretty insignificant at line voltage.

Are incandescent exit signs still common in the US?

Austria almost exclusively used fluorescent exit signs for at least the past 30 years I think. Now they're switching to LED. I've seen some of them, and they hurt the eyes. The small LEDs are extremely bright, contrasting with a dark background.

I have seen some exit signs where the two bulbs are in series. They don't glow full brightness but they last longer I presume.

Yes Ranger, they still have them, but they are falling out of favor now that LEDs are more available.

Back a few years ago, when I was putting up movie theaters, we were also using "nuclear" exit signs. The glow was actually put out by some sort of reaction - had no power source. Someone here can probably shed some more light on what the actual chemical process was for those signs. First time I saw them glowing in the back of the truck it kinda freaked me out a bit...

Ah, yes, those are sometimes used for retrofit jobs here. I've seen them used at an underground railway station where they obviously didn't want to bust up the walls but were forced to put up exit signs. Maybe they also already knew they were going to close down the station in a couple of years and didn't want to put in any money (I think it's going to be closed in 2009 or 2010).

I think I haven't seen any incandescent exit signs newer than some 50 years here... all newer ones are fluorescent, usually one 8W compact fluorescent, older ones mostly with a small battery, power supply and charger inside, newer ones in large buildings tend to be/have to be on a central battery, depends on the size of the bldg.).

3 years ago I did an internship with an electrical company and one of my jobs was running around in the garage of Vienna's court house and prison changing out old exit signs "because the batteries had failed". They claimed they had a power outage some weeks ago and the signs barely lasted 5 minutes. We used a couple of them as portable work lights and 4 hours later they were still going strong... whatever.

Would that happen to be the Bella Terra Cinemas?

I did the audio racks and rough installs for that cinema.

I have an LED exit sign over the front door in my apt. It has a battery backup built in too. Nifty.

That is an interesting idea with the diodes. I want to try that with one or two of the fixtures in my house to see how that works out.

I have a large, antique sign that says "fire escape" hanging over one of the windows in my house as a joke. (1st floor, right next to a door) I pulled it out of a building that was going to be completely renovated. It has 2 lampholders, which were wired in series. on top of that, the fixture was wired for 120 volts but had 240 volt bulbs in it. It barely glowed at all. It looked cool, though, and the original bulbs are still (sorta) glowing strong.

using 240v lamps was the trick we used to get more life out of a bulb change, we used them in stairwells and exit signs and in some places to shine on the fire extinguishers
line voltage just burned out too fast between annual re-lamping cycles.

I still have a few that I use as night lights on my garage and barn

Yeah, ok, but 240V bulbs in series wired to 120V? That means each bulb only gets 60V... now that'll make for a long life

Zapped:



The Nuclear Exit Signs (or "Self-Luminous" Exit Signs) are typically the "Radioluminescent" types, which use the Radioactive Element "Tritium" inside the sign's tubes.

Some may be, or could have been, "Phosphorescent", which uses the same materials as "Glow-In-The-Dark" stuff does, and may be in conjunction with some type of "Photoluminescent" material - a material which absorbs light, then slowly re emits it.

I am more familiar with the Radioluminescent" types, and more specifically, using Tritium instead of Radium + Copper-Zinc Sulfide Paints.

.........HOW IT WORKS...........

The light is produced by the "Bombardment" of ionizing radiation (beta particles, for example).
When the Tritium decays, it produces light.

The half life of Tritium is something like 12 years, so on average a Nuclear Exit Sign using Tritium will last over 20 years.

*** A little Tritium Trivia ***

Tritium ( symbol = T or ³H ) is a radioactive isotope of Hydrogen.
Tritium decays into helium-3 in a single reaction, where the original ³H becomes ³He and releases one electron and one antineutrino.

Tritium cannot penetrate human skin, so the only way to absorb it is by inhailation or ingesting it.

Tritium occurs naturally - from cosmic rays interacting with gases in the atmosphere (Nitrogen, for example); and it is produced in Nuclear Reactors.
It is occasionally a direct product of nuclear fission, and is also produced in reactors moderated with "Heavy Water" (Deuterium).
When the deuterium moderator captures a neutron, a small amount of Tritium is produced.

Tritium is also used with Nuclear Weapons, as the "Fission Primary" (kind of like a Nuclear "Booster" or Blasting Cap), to aid in the detonation of a Plutonium or Uranium weapon.

I have only basic knowledge on this subject - and this information was stored away in my archives, from many years past!
Nonetheless, I might do some research on Tritium + Radiolumenescent materials soon, and post more data later.

Scott

p.s. please pardon any spelling errors!

Thanks for the wealth of info Scott. I think they were definately radioluminescent that I dealt with, as rumor had it that a government agency (nuclear commision?)showed up once when a bunch of the new signs went missing from a storage container on a new build. They interviewed all the company heads and security staff, as I recall.

mxslick - actually, the theaters I was building at the time were Edwards Cinemas. They have since been bought out, I believe by Regal. At the time (around '97 to '00), they were on a building spree, including CA, ID, and Texas. They dumped a ton of money into some very nice theaters, and it's probably what unfortunately buried them. It was certainly fun, however, to get shipped around the country and work with some very cool ECs in different states. We did a lot of the specialized lighting, IMAX, and general finish work. It was a cool gig while it lasted.

Texas Ranger,

it was written that his were wired in series, from my experiences the exit signs were fed with 120v and in Chicago, were ALL fed from a fused panel. but the lampholders were not series'd if that were the case ordinary lamps would have worked just fine for longevity

it was their Code through the late 70s and may still be a requirement

my apologies for adding my own brand of confusing Hoosier gibberish....

It's 2008...and it's still required in Chicago (unless you can get a variance to use breakers).

Yep, but napervillesoundtech definitely had two 240V bulbs series wired to 120V. Pretty dim I guess.

I think the non-electric exit signs I've seen here are photolumiscent rather than radioactive. They're basically flat sheets of some kind of plastic stuck to the wall.

A friend of mine had radioluminiscent paint dating back to WWII in his basement until very recently... now that was cool! Only white walls as long as the lights were on, but in the dark you'd suddenly see a glowing green horizontal line maybe 5 feet from the floor and the word "Ausgang" (Exit) in some script writing painted next to the door.

I saw paint like that on a U.S. Navy ship a few years ago.

A part of the bulkhead was painted with paint that glowed in the dark; and the numbers telling you where you were had been painted in black letters on it.

When the lights went out, you could see the tags easily on the glowing background and knew just where you were in the ship (and how to get where you really wanted to be).

Sorry to go way off topic (to a degree), guys,
I was reading an article in the June 1988 edition of Electronics Australia (yes, I collect these mags) and the article was talking about Geiger counters.

What sparked my interest about this article was that the author mentioned things like clocks and watches that had "glow-in-the-dark" faces and hands.

Now, the author was talking about after WWII when ladies were working in the clock and watch-making factories of places like then-Russia, to apply the paint to the certain parts of the face, etc they would dab the end of the brush on the end of their tongues, to help get the paint (which contained all sorts of nastiness) to stick to the metal.
Thousands of women died later on, at quite early ages, through what was known as "Radium Jaw".

Apparently, if you can find an old clock or watch that has one of these faces on it, you can still get quite a high reading of radio-activity with a Geiger counter.
We never used to worry about this sort of thing years ago, mind you, we have gone digital since then.

My apologies if I've taken this thread too far off topic.

Yes, my dad told me that long ago, the part with the radioluminescent hands... but he also said they only emitted alpha rays already blocked by the glass. Of course if you ingest that stuff or get it into your mouth... ouch!

My current wrist watch seems to have had such hands once... but they don't glow in the dark any more, they just react to UV light. No idea how old it is, it's a quartz wristwatch my grandmother gave to me (it once belonged to my grandfather).

Mike,

Ottawa, Illinois had two factories that painted watches in the same fashion

http://www.roger-russell.com/jeffers/radiumdials.htm

There may be a good reason though. Many LEDs have a PIV (Peak Inverse Voltage) rating which is nowhere near as high as the PIV for a conventional silicon diode. When you run them on A.C., putting a diode in series will prevent the PIV of the LED from being exceeded.

I am guessing the LED exit sign has protective diode inside. I like one forward biased in front of the LED and another reverse biased across the LED but that is a belt and suspenders approach. This was in my "capacitor voltage drop" scheme on an SSR.