Carlos from Spain:
the cover could be dark when looked from the outside but clear from the inside like some tinted windows or see through mirrors with unidiretional filters but definately looks more clear in that picture you posted
My work with illuminated displays lets me speculate a bit.
The "black" effect probably works this way: For a given tint level, the attenuation of the headlamp output is only half as much as the reflected light originating from outside the cover. This is because reflected light has to make two trips through the tinted covering while the light originating inside the fixture only has to pass through the tint once.
If the tint has 15% light loss, the headlamp will be dimmer by 15% (0.85 of original level) when using a tinted cover but the reflections will be 0.85 x 0.85 or lose about 28% of the non-tinted value.
It's the same deal as window tints. Make sense?
"One-way" mirrors work by the same principle. They are "mostly" reflective, but maybe only 90% reflective. They let 10% (or so) of the light pass through to the other side. The observer sits in a darkened room for two reasons. 1) because the image seen through the back of the mirror is somewhat dim, and 2) because if the observer had lots of illumination, the 10% of the room light that made it from the observation room into the main event room might be bright enough to "leak" through the mirror effect and reveal the observers to the observed.
Mirrored sunglasses anyone?
--
Mike
2005 Carrera GT - Signal Yellow
2008 Tesla Roadster - Thunder Gray
1972 BMW 3.0 CSi - Nachtblau
2009 Bentley Arnage T - Black Saphire