Greaser,
Krypton, and Xenon are used in bulbs as they are more thermally efficient than argon which is typically used.
(As it turns out, argon and the argon-nitrogen mixture are not the best. Krypton conducts heat less than argon does, and xenon conducts heat less than even krypton does. So these are better than argon for more efficiency.) Xenon, and Krypton gas have larger atoms than argon which allows the evaporated tungsten filament to be "bounced back" onto the filament instead of be deposited on the glass bulb.