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I know, I know, this is a really naive question. I do know that lume is a substance painted onto watch hands and hour markers to make them visible in the dark, but what I'm getting at is just what is that substance and how does it work? Does it somehow take on light when exposed to it, slowly losing its visibility when deprived of light? What's the story here?
 

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http://en.wikipedia.org/wiki/Phosphorescence

An extremely simplified explanation is that in pretty much any material, electromagnetic radiation will bombard electrons and excite them, which will then give off the energy again in electromagnetic radiation. Thus a desirable substance for a watch luminescant is one whose electrons will be excited by radiation which is relatively abundant in the environment, will release the energy via radiation in the visible spectrum, and will do so slowly.
 

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Great references, spluurfg and Mike. Thank you. It would appear that (a) the lume on almost all watches is the RC Tritec product Super-LumiNova and (b) that this product is strontium aluminate. My understanding from these references is that the strontium aluminate, which is free of radioactivity, becomes activated by exposure to light, with the activated molecules then emitting light, via a slow-degradation process, for a number of hours, until the activated particles become deactivated, with the cycle begun again only with exposure to light.

I've noticed the lume on my watch dial decline in brightness through the night, starting out very bright, but much less so by morning. One factor, I guess, would be how much exposure to light the watch gets during the day. In the fall/winter/early spring seasons, I generally wear long-sleeve shirts, with the only real exposure to much light occurring when I pull my sleeve back to see the time. Does anyone know just how much exposure is needed to get the lume sufficiently activated to produce visibility in the dark for a whole night (say 8 hours)? If the watch is kept in a drawer, does the lume simply produce no illumination whatsoever until a period of exposure to light?
 

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It depends on the luminova/superluminova compound chosen by the watchmaker at the time they spec the dial as to whether it will glow for the entire night. Some lume will charge and glow many hours with as little as 30 seconds exposure to incandescent light at a distance of 300mm. Remember that your night vision is part of your peripheral vision. Looking directly at your watch once your eyes have accustomed to the dark is a mistake. You will be trying to focus on the face with your "day vision", in essence a blind spot, at night. Also, the inverse square law applies as it relates to electromagnetic radiation. That means that after some hours if you hold up the watch close to your eye the brightness will double as you halve the distance to your eye. No point in trying to read the dial at arms length if you can get a proper read simply by bending your arm and bring the watch closer to your optical nerves. :)

As for tritium coated dials, the lumi is not charged by exposure to light. It is a constant emitter but at lower levels then you will see with newly charged superluminova dials. It is however constant over the entire nighttime period so is predictable once you understand its performance and how to get a read off the dial using peripheral vision.

I hope this answers some of your questions.
 

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Remember that your night vision is part of your peripheral vision. Looking directly at your watch once your eyes have accustomed to the dark is a mistake. You will be trying to focus on the face with your "day vision", in essence a blind spot, at night.
Well that's reassuring! I always thought the centres of my retinas must have been damaged, as on watches with very limited lume I find it a little hard to make out the 'double dot' at 12.

Tom
 

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The technique is to let your eyes relax, literally unfocused (as if trying to see the tip of ones nose), and observe the resulting field that comes into sight. If you don't tense its possible to maintain that peripheral awareness for many minutes at a time. It should not be a strain but a very easy change in how you observe the world. Enjoy!
 

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A while back I noticed that lume on my watches will stay 'lit' longer when charged with different light sources. The sun is the best - the lume on my Bathys glows like a torch when I come in from bright sun and stays lumed for hours. But at night (no sun), I used to 'charge' the lume with the bedside lamp. The result was kinda bright at first, but then fading quickly.

After reading some posts on lume, I bought a 3 watt LED flashlight (a Surefire - and yes, I know it's overkill, but I needed a flashlight anyway;-)) and I now use that to 'charge' my watch. The result is several hours of nice, bright lume on a charge of about 20-30 seconds.|>
 

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Its all about the absorption spectrum of the dyes used in the lume - in most cases its most responsive to the UV spectrum,and you get a lot more UV light from the sun than from indoor lighting. This is also why a UV flashlight is great for charging lume.
 
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