Fill your cup with water and illuminate it from the bottom. Voila!
The water in the cup acts like a light guide when illuminated from the bottom. Add a Luminated Decal, and it is visible in the daylight AND it lights-up when the cup is illuminated from the bottom.
The tumbler shown uses a labels, but the technology works equally well if printed directly on the tumbler.
The tumbler shown does not have a label on the back side (note that faint Fresnel-type image reflections can be seen). Note that a contrasting label can be placed in contact with the backside of the tumbler. Also, the brightness of the front label can be enhanced by adding reflective material on other portions of the tumbler.
Yes, it works on both insulated and uninsulated cups as shown in the pictures. With insulated cups (that use a cup-in-a-cup with air in between the two), the decal needs to be on the outside surface of the inner cup. As shown, certain insulated tumblers are made such that the inner and outer cups can be separated by simply unscrewing them. In that case, unscrew them, add the decal to the outer surface of the inner cup, and then screw them together again. Alternatively, if the insulation factor is not needed (permanently or just for a period of time), the cups can be made to fill the air gaps with water (or other clear fluid) to allow the decal to be used on the outer cup. To regain the use of the insulation, simply drain the water from the gap.
Use colorful fluorescent markers (including white) to personalize the decal and the surface it's on - the markings will light up as well!
In addition to drinking vessels, a decorated tumbler can also be used as a night light when filled with water (and sealed with its lid) and placed atop its LED base. Collections of tumblers (e.g. think superheroes, family photos, artwork, sports teams, etc) can be illuminated.