Fred H. from Salt Lake City Utah, USA asks:
Thanks guys for the work on your blog, keep the pictures & reviews coming. My question today is: other than color is there a difference between green & blue lume? Also what advantages do Superluminova & tritium gas tubes have over regular lume? Finally, is there a minimum amount of light needed for lume to be really useful? For that matter is there a maximum amount of light exposure beyond which the lume will not work any better in the dark?
This is a larger subject matter and you ask a lot of great questions. Lume is a very important element on many watch dials that allows for night viewing. Traditional luminant is charged by light and then outputs a glow at night that decreases over time until the luminant is charged again. The most popular type of lume is SuperLumiNova, from the company “LumiNova.” SuperLumiNova is very popular among high-end brands but there are some alternatives. Seiko uses its own lume, sometimes called “Lumibrite,” for example.
Luminant must be charged by light, and the amount of time required to charge depends upon the brightness of the light. Sunlight is the best and just a few minutes will really charge up lume well. Indoor lighting doesn’t fare as well. The more UVs the better. Below we have more information on the brightest luminant colors.
Tritium is a totally different type of lume that involves small, self-glowing tubes produced by Swiss MB Microtec H3. These tubes contain small, safe amounts of radioactive material and they come in various colors. While not as potentially bright as SuperLumiNova, tritium tubes don’t need to be charged with light and will glow all night long. Tritium tubes tend to work for about 25 years until they need to be replaced.
Luminosity is measured in units called “lux.” The standard for measuring lume is ISO 17514. The absolute minimum visible light is 1e-5 lux. You need instrument-grade hardware to measure that. Here’s a plot showing 3 lume watches versus a tritium watch. Note that the tritium is constant at about 0.0004, and the lume is initially much brighter, crossing over around 200 to 5000 seconds later.
You can get more information on lume from aBlogtoWatch contributor Paul Hubbard’s page.
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