Hi Andy
In fact, there are three types of illumination.
– A small light bulb
– LED backlight
– Electroluminiscent.
Small Light bulb – was used in older watches – the seventies – early eighties. Almost all brands Seiko Citizen Casio and Timex Cessel many others. But in the eighties and the latch at the end of the eighties could find the bulb in such a watch as Montana.
LED backlight – e.g.some of the Gshock models are LED backlit, Swiss Army/Victorinix sells a Night Vision line that is LED illuminated ($300-600$). LEDs usually gave backlight in green, but sometimes it was the color of amber.LEDs were also used in his later versions casio db, such as Casio DB-520.
Electroluminiscent backlight – used in some Casio watches called as “Fox Fire”.The Timex corporation has its very own similar technology called “Indiglo”.Some of G-Shock has Illuminator (where the “E” of the model number means Electroluminescent) gives a blue/green light.
Best
.
