Most of us have seen the police drama with the suspect being questioned in one room and witnesses or other police personnel behind one way glass in another room. If you’re like me you’ve thought, “How cool is that?” Cool yes, but sometimes with marketing research rooms, retail management areas, security stations, or other sensitive places this cool effect can be vital.
One way view through glass is a commonly misunderstood effect so let’s first identify the most important variable in achieving one way view: light control. You’ve probably witnessed clear glass providing one way view and not thought much about it. When outdoors on a bright day, with the sun high overhead, you look toward an interior space and all you can see is your reflection in the glass. This is caused by the high ambient light outdoors being reflected from the surface of the clear glass back to your eye. The higher the angle of the light source and the brighter it is (overhead sun in this case) the more surface reflectivity you’ll perceive. Add to this a relatively darker interior space and the brightness of the reflected image overwhelms the light coming from the interior. Get close to the glass and shield your eyes from the ambient light around you and you’ll be able to see through the glass.
So if we want one way view through glass how do we stack the deck in our favor? The best retrofit method is to install a dark, dual reflective film on the glass. A dual reflective film can be as much as 40% more reflective on one side compared to the other. Being dark it also allows less light transmission from one side to the other. This means there is less of whatever light is on the private side to reach the public side, and less light from the public side can penetrate the glass to illuminate the private side. High reflectivity toward the public side essentially makes the glass a mirror from that side and achieves the goal. Understand that even using film with such properties light control is crucial. If the glass in question is an exterior panel then at night, with lights illuminating the interior space and darkness outside, even such a film can be overcome and the one way effect somewhat reversed. Having bright lights outside the glass and keeping interior light at a low level will keep the view versus privacy going in the right direction.
Another, though less common, way of achieving one way view is with a perforated graphics film. These films are typically used for printed signs and graphics on glass. Such a film is an opaque vinyl film, white on one side and black on the other with small, regularly spaced holes in it allowing it to be seen through. The white side reflects light back to the eye and the black side less so. Again, keeping the private side darker is key.
If you need one way view on existing glass the best way to move forward is to consult a window film professional. They can make recommendations and show you samples based on your particular situation and needs.