Re: How does the 'all day' part of 'all day Indiglo' work?

Timex says on their Company History Page:
Today, more than 75 percent of all Timex watches are equipped with the "Indiglo" night light. All-Day Indiglo, a hologram-like material, provides greater contrast between digital numbers and the display background.

A holographic reflector is basically a reflecting diffraction grating. Basically, there are two types of reflecting gratings, relief types and volume types. Today, relief type reflection gratings can be made which behave like white reflectors. This is done with computer generated hologram techniques. For certain values of the incoming and outgoing angles, the reflection is white. However, next to this white region there is a red region on one side and a blue region on the other. The positions depend on the angles of the incoming and outgoing light rays and on the exact structure of the grating. Also, these reflectors can be made to reflect for example green in a certain direction, and they reflect red in another direction.

Volume type reflection gratings are made of layers with alternating refractive indices. Also here, there is a distinct dependence on the angles of the incoming and reflected beam.

I cannot tell you exactly which type of grating Timex uses for their All-Day Indiglo.

Here's a link to the How Stuff Works Page about how the Indiglo part works.

Here's a link to Encyclopeadia Brittanica about diffraction.