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My current research is about measuring the optical properties of window systems. Specifically, we are
building a device that will be able to quickly measure the bi-directional transmission or reflection
distribution functions (BT(R)DF) of window systems. These devices, called goniophotometers, are well-established
tools used for analyzing the behavior of light through (or off of) window systems. Our goniophotometer uses an innovative
approach first proposed by Greg Ward in which a mirrored ellipsoid reflects light that has been transmitted through or reflected off
of a sample into a digital camera. The digital camera, either a charge coupled device (CCD) camera or an Indium Gallum Arsenide
(InGaAs) near infrared camera, will be calibrated as either a photometer (CCD) or radiometers (CCD and InGaAs) to measure the luminance or radiance
emerging from window samples as a function of the angle of incident radiation and the angle of emerging radiation. A simple schematic
of the device is shown below. A presentation about the current state of the research is available here. The
image on my home page is the view our CCD camera sees through a fish eye lens of a foamboard box used to correlate pixel locations
with angular directions. For our detailed description of the research go to the following page: Research Outline
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The purpose of this research is to support the development of angularly selective, or light redirecting window systems
that may have applications for improving daylighting or thermal performance of buildings. This new goniophoto/radiometer should provide major
improvements in the time required for goniophotometric or gonioradiometric analysis of fenestration systems. Another
innovation of the device will be its ability to analyze light redirection over a broader range of the solar spectrum. Using
the InGaAs camera, which is sensitive to radiation of wavelengths between 900 and 1700 nm, the majority of the near infrared component of
solar radiation can be observed and included in BT(R)DF assessment. Our goal is to be able to quickly charactize the spectral and
directional changes to radiation that window systems cause over a broad spectrum of incident solar radiation.
As a complementary project to building this measurement device, I hope to design a window system that limits near infrared gains
during the summer months while maximizing near infrared gains during the winter months, while at the same time providing acceptable
levels of visible light transmission during the entire year for good daylighting.
This material is based upon work jointly supported by the Massachusetts Institute of Technology and by the National Science Foundation under Grant No. 0533269. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).
Private research pages
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