When was the Surefire 6V Universal Weaponlight first released?

[Jpax]

Does anyone know when the Surefire 6 volt universal weaponlights were first released? I'm talking about the 600 series lights such as the 660.

 

[lightfooted]

I think it was in the late nineties...1998 or '99. I'm not real sure though.

 

[Jpax]

Definitely much earlier than that, I've read 1988 but looking for solid evidence.