Q & A: Timex Indiglo Watches

What makes Timex Indiglo Watches glow blue/green? and how does it glow? Is there some solution, or material that glows when an electrical current is passed through it? or is it simply a green light?
- Cameron Jones (age 19)
University of Illinois, Champaign, IL, USA

Cameron -

Here's what the Smithsonian Institute has to say about Timex Indiglo® Watches:

"Timex received the patent for the Indiglo® nightlight in 1988. The nightlight's bluish green light illuminates the entire dial of the watch evenly at the push of a button. The dial is coated with a compound of zinc sulfide mixed with copper, a substance which becomes luminescent when an electrical charge is applied. This layer is sandwiched between two conductive layers which act as electrodes. When the button is pushed, energy is supplied by the battery across the two electrodes, which in turn lights up the dial."

Hope this helps. For more information, check out the
Timex Webpage.

-Tamara

(published on 10/22/2007)

I have read you answers to the indiglo watch questions and you state that the compound is Zinc Sulfide mixed with Copper. Can you tell me exactly the proportions of this mixture? I am interested in trying this out at home. Another question is that I have seen indiglo objects that can change colors with the flick of a switch, an example being the new indiglo gauges that I bought for my car that change from blue to green just by clicking a switch. How is this done?
- Chris (age 18)
Courtland High, Fredericksburg, Va, USA

Chris -

One part at a time. First of all, this is a pretty major project to just 'try at home'. The materials and the process for doing this are not just hard-to-find, but difficult to do successfully without special equipment.

Zinc sulfide and copper are only one of many mixtures that will work. The important point is that you have a 'phosphor' (like zinc sulfide) with other stuff mixed in. I don't know the exact proportions, but they use a large amount of the zinc sulfide and 'dope' it with just a little bit of copper (or whatever else they're using). 'Doping' is a technical word that basically means 'mixing in just a little bit'.

The whole mixture gets pressed between two electrodes (the top one of which is transparent) and hooked up to an alternating current (AC). When the power is turned on, it creates a strong electric field that activates the dopant (the stuff that's mixed in), making it produce light.

A great picture of how this all goes together (along with most of the information I've got here) comes from Britannica Online.:



Your second question is easier... Depending on which dopant you use, you'll get different colors. For example, a mixture of copper and chlorine gives blue light. Copper and aluminum make green light. And copper, chlorine, and manganese together make yellow.

To make something that can switch between two different colors, all they have to do is make two sets of layers. One is made with copper and chlorine, for example, and another with copper and aluminum. Each layer has a separate pair of electrode layers and each one is hooked up to a separate alternating current. Flipping the switch just changes which 'sandwich' gets turned on.

-Tamara

(republished on 07/28/06)

Another question about the Timex Indiglo. You mentioned that "the dial is coated with a compound of zinc sulfide mixed with copper, a substance which becomes luminescent when an electrical charge is applied. " Now, does this compound get used up over time? People have told me that once the compound used up, it won’t glow anymore. Is that true?
- John (age 20)
Northeastern University, Boston, MA US

John,
Indiglo watches take energy from the watch battery and give it to the atoms in the zinc sulfide-copper compound. This energy is then given off as light. After the atoms give off this light they are exactly the same as they were before they got the energy from the battery. So the answer to your question is: no, the zinc sulfide-copper mixture does not get used up when you use the indiglo light.

-matthew

(republished on 07/28/06)