Quote:
Originally Posted by dorkdog
I'm looking for a watch with hands and points that will stay lit at night the longest. I do not want a digital watch. Are there any watches out there that use LED technology (like angel eyes) to light the hands/legend at night so it doesn't fade?
Thanks
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By far, the brightest illumination on a watch will be tritium (H-3) tube variety. Next will be what is called Superluminova. Next comes standard lume, which is anything other than the prior two.
After something like 25 years, the luminosity on tritium tubes will fade entirely and the tubes have to be replaced if you still want the glow-in-the-dark functionality. The reason for that is that tritium's half-life is a bit over 12 years. So long as beta-decay is happening, they will glow. Their glow isn't affected by exposure to light; it's an atomic process governed by the "weak force." The more tritium int he tube, the brighter the glow.
Some folks will cite concerns about the fact that H-3 is radioactive. Exposure to radioactive H-3 could cause problems; however UK scientists determined that unless one is directly exposed,
i.e., not through a plastic tube or even a plastic or glass crystal, there is no risk or cause for concern. In other words, don't disassemble your tri-tube watch and then break open the tubes.
Superluminova is strontium aluminate (SrAl(2)O(4) or just SrAlO) that is branded as "Superluminiva." will fade after about 4 hours. Technically, there is some glow out to about 10 hours, but you need pretty good vision to detect it. After the glow fades, it needs to be "recharged" by being exposed to daylight. I don't know how many years it takes for the glow-recharge-glow-again capability to entirely disappear, but as the half-live of Sr is nearly double that of H-3, I would imagine that one can repeat the process for longer before having to replace the SrAlO coating.
As SrAlO coatings go, there is a noticeable difference in the brightness of higher and lower quality coatings. The brighter ones will be made from coatings (paint essentially) having larger SrAlO crystals.
How can you tell who uses coatings with larger crystals and who uses smaller ones? As a practical matter, short of asking the manufacturer to tell you the crystal size or to tell you who made the coating for them so you can then ask that manufacturer, I have no idea. Academically speaking, there are probably several ways to tell, all of which involve things like light meters, measuring sticks, magnifying glasses and microscopes.
Prior to SrAlO, copper activated zinc sulfide (ZnS) was used to provide luminosity in lieu of H-3. I don't know the half-life of ZnS, but I have several watches that are ZnS driven lume and that are are 10+ years old. I can't see squat on those dials in the dark. It doesn't matter whether they are pricey watches or inexpensive ones. If I want to read them in the dark, I need an external light source of some sort. By my best estimation, they all stopped glowing somewhere around three to five years into my time of owning them. As a practical matter, this matters to me only when I wake up in the dark and there's neither a light nor electric clock nor cell phone I can use instead. In other words, I don't give a sh*t.
All the best.