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Green: Daylight Redirecting Film

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Judhajit Chakraborty, Assoc. AIA, LEED AP WSP Built Ecology

We all know the benefits of day-lighting and how important it is in our designs. Buildings with abundant natural light have been shown to:

• Increase employee productivity in offices
• Boost retail sales in stores
• Improve student test scores and attentiveness in schools
• Decrease rates of absenteeism
• Improve patient recovery times in hospitals and health centers
• Reduce energy costs

There are many strategies to effectively day-light a space without compromising too much on glare. Worth mentioning there are two categories of glazing in a unit – Vision glazing mostly for views and protected by blinds, and daylight glazing mostly for daylight which, with effective strategies, can be blind free.

October_ArchNews DRAFT pg 1-5_Page_5_Image_0002The image on the left shows the daylight and vision glazing positions of a single glazing unit. Also on a fully glazed surface, the glazing from the floor level to 1’ is the least useful in terms of both views and day-lighting. The image also shows a typical light-shelf for redirecting light to the ceiling for daylight.

This article is about a new product which acts as a light-shelf but it has the power to throw light much deeper into the space. The product also known as the Daylight Redirecting Film or DRF, is a film consisting of many micro-prisms which optically redirects over 80% of the light incident on the glazing upward. There is another diffusing film which distributes light uniformly over greater ceiling depths. In doing so, the film: reduces glare and discomfort caused by direct sun, redirects natural light to as much as 40 ft, extends daylight zone to 8ft for every feet of daylight glazing with DRF, and provides up to 50% lighting energy savings over a comparative baseline. The DRF technology is very new and there are only a couple of players in the market, the most prominent among them is 3M. The image below shows how the 3M Daylight Redirecting Film works.

 

October_ArchNews DRAFT pg 1-5_Page_5_Image_0003As shown in the image to the left, the assembly includes a double glazing unit or an IGU (Insulated Glazing Unit) and the DRF film is placed on Surface no 2 as shown in the enlarged image. The assembly comes with a diffusing film on Surface 3 which distributes light uniformly towards the ceiling. Extensive tests have been done on this DRF technology especially with the 3M film at the LNBL lab and at the newly constructed Net Zero Sacramento Municipal Utility District (SMUD) building. All the reports are available upon contacting any 3M rep.

As promising as this product seems to be, there are some limitations; since the film is applied on Surface # 2, then there is no scope for any low-e coatings as they also go in Surface 2 and the technology is such that currently the film can only go on even numbered surfaces. Upon asking 3M reps mentioned that they will be launching a product early next year which will combine both the films into one. Also in terms of simulation, there are some challenges with predicting glare as no daylight calculating engines are robust enough to smoothly analyze the micro-prisms. But nevertheless, this is a product worth trying out.

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