There is more than one visor, the protective visor and the sun visor.
"The protective visor is an ultraviolet-stabilized polycarbonate
shield
which affords impact, micrometeoroid, and ultraviolet
ray protection. It can be positioned anywhere between
the full-UP and full-DOWN positions and requires a force of
2 to 4 pounds for movement. A coating is added to the inner
surface of this assembly. The elastomer seal on the upper
surface of the stiffener prevents light passage between the
two visors.
The protective visor can be lowered independently
of the sun visor, but cannot be raised independently with the
sun visor in the DOWN position.
The inner surface of the polysulfone sun visor has a gold
coating
which provides protection against light and reduces
heat gain within the helmet. The visor can be positioned
anywhere between the full-UP and full-DOWN positions by exerting
a force of 2 to 4 pounds on the pull tabs. The sun
visor cannot be independently lowered unless the protective
visor is in the DOWN position, but it can be raised or lowered
independently when the center eyeshade is in the full-UP
position and the protective visor is in the DOWN position."
http://www.hq.nasa.gov/alsj/alsj-EMU1.pdf#page=92