Daylight redirecting film (DRF) is a thin, flexible plastic film which can be applied to a window to refract incoming light upwards, so that the deeper parts of the room are lit more evenly. It is a lighter modern version of glass prism tiles. It can be used as a substitute for opaque blinds.
Video Daylight redirecting film
Manufacture
Daylight redirecting window film was initially made of one redirecting film and one glare-reducing diffusing film, often located on different interior surfaces of a double-glazed window, but integrated single films are now available. Daylight redirecting film is made of acrylic on a flexible polyester backing, one side coated with a with a pressure-sensitive adhesive.
Daylight redirecting films are often configured to bend light sharply, throwing it upwards to the ceiling, where a typical ceiling diffuses the daylight somewhat deeper into the space.
Maps Daylight redirecting film
Function
The human eye's response to light is non-linear. If light is redistributed from the brightest parts of a room to the dimmest, the room therefore appears brighter overall, and more space can be given a useful and comfortable level of illumination (see before and after images from a 1899 article, left). This can reduce the need for artificial lighting.
Refraction and total internal reflection inside optical prisms can bend beams of light. This bending of the light allows it to be redistributed. Daylight redirecting film is moulded with thin near-horizontal voids protruding into or through the acrylic; the slits reflect light hitting their top surfaces upwards. Refraction is minimized, to avoid colouring the light.
Many small prisms may be joined at the edges into a sheet. A prism sheet is somewhat like a linear Fresnel lens, but each ridge may be identical. Unlike a Fresnel lens, the light is not intended to be focused, but used for anidolic lighting.
While the films do save energy from lighting, the saving vary substantially by climate, aspect, electricity costs, and existing lighting type. At 2014 costs, including labour, payback time may be measured in decades.
See also
- Prism lighting
- Window film
References
Source of the article : Wikipedia
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