These pretty strips of light are plastic diffused backlights, often seen in LCD displays. Normally they're tucked behind the LCD and shine white light from below. Here, they've got the LEDs available individually and they're really cool! Each LED is encased in a 3.5mm thick strip of a acrylic. The acrylic strip is a special type that is very good at diffusing light, so even though there is only one single white LED, it provides near-uniform lighting. The other flat side of the strip has a reflector on it so you only get light from the top (otherwise the backlight would lose 1/2 the brightness unnecessarily)
You can treat this backlight just like an LED, light with ~3V at 20mA current and you get a pretty shape that you can mask with vinyl or draw over with marker. Gels can be used to change the color. Adafruit think these would make great theyarables without the need for EL or inverters, they're much brighter than EL and use less battery. The trade-off is these are not flexible at all.
This particular backlight has a 0.5" by 1.5" (12mm x 40mm) lit area
White LED Backlight Module - Small 12mm x 40mm (4:16)
- Weight: 1.6g