Metal halide or mercury vapor luminaires in a multi-purpose type occupancy (such as a gym) need a lens. Metal halide fixtures need a lens always, unless they are a "type O" or a "type PAR".
At least, thats what I remember reading. Anyone else?
[This message has been edited by Ryan_J (edited 01-10-2005).]
Another nice resource for this is the ROp and ROC.
Regarding the lamps, they have a dimple in the end of the lamp, and the base is right between medium and mogul, making them compatible only with a type "O" fixture.