Timex Indiglo Watches

Most recent answer: 10/22/2007

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 has to say about :

"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


(published on 10/22/2007)

Follow-Up #1: Indiglo Green, Indiglo Blue

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 .:

Producing light

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.


(published on 10/22/2007)

Follow-Up #2: More Indiglo

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

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 can be exactly the same as they were before they got the energy from the battery. .


People say that this Indiglo effect does wear out after long use, however.  I bet what happens is a small amount of electromigration of atoms: under the influence of the electric field, atoms gradually get dragged out of position. As Matt said, it's not that the chemicals are getting used up like in a battery or a fuel tank. It's more that they just wear out, like the mechanical parts of an engine. In principle, they gradually wear out just by random thermal diffusion of the atoms, but it sounds like the electrically driven motion is more important under normal use.

Mike W.

(published on 10/22/2007)

Follow-Up #3: Indiglo wearing out

My timex Indiglo watch only has a tiny illumination at the bottom if the watch when I push the stem. I got a new battery and it still doesn't fix the problem. Can it be fixed?
- Mary Lee (age 63)
Glenolden, PA

Mary- In response to your question, I've modified the previous answer in this thread, which didn't seem quite accurate.

Mike W.

(published on 05/28/2013)

Follow-Up #4: indiglo failure

I don't see any real answer to Cameron's question. My battery is fine but the indiglo has stopped working. What if anything can I do about that? Simple answer please.
- Greg (age 78)
Appleton, WI USA

Did it gradually stop working? If so, the best guess is that you have the same problem that everyone else has. The atoms in the Indiglo device (maybe mostly in the form of Cu++ ions) get dragged out of place by the electric field. That gradually destroys the device.

Mike W.

(published on 01/20/2017)