Daylight redirecting film (DRF) is a thin, flexible plastic film which can be applied to a window to refract or reflect incoming light upwards, so that the deeper parts of the room are lit more evenly. It can be used as a substitute for opaque blinds. It is a form of

prism lighting Prism lighting is the use of prisms to improve the distribution of light in a space. It is usually used to distribute daylight, and is a form of anidolic lighting. Prism lighting was popular from its introduction in the 1890s through to the 19 ...

Function

The human eye's response to light is non-linear: halving the light level does not halve the perceived brightness of a space, it makes it look only slightly dimmer. 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 an 1899 article, left). This can reduce the need for artificial lighting.

Refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

and

total internal reflection Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...

inside optical prisms can bend beams of light. This bending of the light allows it to be redistributed. The prism structure only bends light appropriately at certain angles; if the angle of incoming light changes, a variety of prisms or a movable prism awning may be needed. While the films do save energy from lighting, the savings vary substantially by climate,

aspect Aspect or Aspects may refer to: Entertainment * ''Aspect magazine'', a biannual DVD magazine showcasing new media art * Aspect Co., a Japanese video game company * Aspects (band), a hip hop group from Bristol, England * ''Aspects'' (Benny Carter ...

, electricity costs, and existing lighting type. At 2014 costs, including labour, payback time may be measured in decades.

Window film Window film (tint) is a thin laminate film that can be installed to the interior or exterior of glass surfaces in automobiles and boats and also to the interior or exterior of glass in homes and buildings. It is usually made from polyethylene ter ...

s are also used for cooling and heating energy saving, and to block UV.

Manufacture

Daylight redirecting film is made of

acrylic Acrylic may refer to: Chemicals and materials * Acrylic acid, the simplest acrylic compound * Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity * Acrylic resin, a group of related thermoplastic or thermosett ...

on a flexible polyester backing, one side coated with a

pressure-sensitive adhesive Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is a type of nonreactive adhesive which forms a bond when pressure is applied to bond the adhesive with a surface. No solvent, water, or heat is needed to activate the adhesive ...

(to make it peel-and-stick). There are two types of film. Some film is moulded with tiny triangular prisms, making a flexible peel-and-stick miniature prismatic panel. The prisms are joined at the edges into a sheet. A prism sheet is somewhat like a linear

Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the c ...

, but each ridge may be identical. Unlike a Fresnel lens, the light is not intended to be focused, but used for

anidolic lighting Anidolic lighting systems use anidolic optical components to light rooms. Light redirected by these systems does not converge to a focal point or form an image, hence the name (from ''an'', without, and ''eidolon'', image). Anidolic lighting us ...

. Other 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. The slit-based films are more transparent (both are translucent), but when the sun is high, they tend to send the light up at the ceiling, not deeper into the room. Prism-based films are translucent rather than transparent, but offer finer control over the direction of the outgoing light beam; the film can be made in a variety of prism shapes to refract light by a variety of angles. Prism-based films are a lighter modern version of glass prism tiles. 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.

References

{{Reflist , refs=f {{Citation, last1 = Padiyath, first1 = Raghunath, author2 = 3M company, St Paul, Minnesota, title = Daylight Redirecting Window Films, access-date = 2017-10-09, date = 2013, series = U.S.A. Department of Defense ESTCP Project number EW-201014 , url = https://www.serdp-estcp.org/Program-Areas/Energy-and-Water/Energy/Conservation-and-Efficiency/EW-201014 Daylight Redirecting Window Film
Energy Efficiency Emerging Technologies. E3tnw.org {{Citation , editor1 = Henry Crew, Ph.D., editor2=Olin H. Basquin, A.M. , title = Pocket Hand-book of Electro-glazed Luxfer Prisms containing useful information and tables relating to their use For Architects, Engineers and Builders. , year = 1898 , website = Glassian , url =http://glassian.org/Prism/Luxfer/Handbook/page1.html Object of the Moment: 3M Daylight Redirecting Film by 3M
by Selin Ashaboglu, March 02, 2017 Solar architecture Energy-saving lighting Prisms (optics) Plastics

Function

Manufacture

See also

References