Mirrored and One Way Window Film for Privacy and Security
Reflective "mirror" film is primarily a solar control window film which happens to have the added feature of doubling up as a privacy film.
This is the perfect window film product where "one way" daytime privacy is required through external facing windows. Outward vision is unobstructed while inward vision is obscured. Ideal as a visual security safeguard to protect personnel and equipment from prying eyes.
"One Way" or "Two Way" film as it it is sometimes called is not as effective on internal screens or where privacy/security is required at night time. When it's dark outside and the lights are on inside the privacy effect is lost.
To achieve "one way vision" between two internal rooms or offices the room requiring vision in should be lit around seven times brighter than the room requiring vision out. This is not too difficult to achieve as long as it is fully understood that one room will be effectively unlit.
For a full explanation on how reflective window film can be used in this way please see below.
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How does one way / two way glass film work?
Picture the scene - In any TV crime drama where an identity parade is taking place the “line-up” always stands in a brightly lit area while the viewers are always in a darkened room observing through "one way" glass.
"I want to see out, but want to prevent people from seeing in" is a common remark heard almost on a daily basis by anyone involved in the business of supplying or installing window film. The reality however is quite different than simply applying a layer of reflective window film to a pane of glass to achieve "one way vision". The secret lies not in the film or the glass but in the prevailing lighting conditions.
Buildings with "mirrored" windows are now a common sight in most of our towns and cities. This is usually glass treated at point of manufacture with a reflective coating or windows that have been retrospectively coated with a reflective solar control window film. The reason why these windows appear mirrored from the outside yet can be viewed through from the inside is due to their metallised coating and the differential in external and internal light levels.
Why does one way window film not work at night?
The installation of reflective window film or glass within the external facade of a building does indeed afford privacy to the occupants but only during daylight hours. During the hours of darkness with internal lighting in operation the windows become "see through" from the outside.
Because external facing windows often only require "one way" vision during daylight hours such as offices, night time transparency is not usually an issue.
Why is the mirror film you installed on my windows not working?
When the requirement for "one way vision" concerns internal glazing such as office partitions or vision panels the effect is much more difficult to achieve and in many cases nigh on impossible. Unlike external glazing, internal windows usually have similar amounts of light present on both sides of the glass. Should the light differential between the "private" side and the "viewing" side be less than a ratio of 1:7 this will probably result in total transparency or total obscurity from both sides no matter which way round the film is installed onto the glass.
To overcome this issue in an office environment where you have a window dividing two internal spaces, additional lighting can be introduced to one side of the glass or alternatively the amount of light on one side can be greatly reduced to produce the “one way vision” effect.
There is absolutely no exception to this rule. One way / two way vision glass or film does not work by magic but simply by the laws of science.
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