Ian Edmonds

Performance of laser cut light deflecting panels in daylighting applications

Abstract The manufacture, application and performance of a material which combines light deflecting properties with good viewing transparency is described. The material, of similar thickness to conventional glass glazing, is produced by laminating laser cut acrylic sheet between sheets of glass. It is designed to replace glass in in clerestory windows and atria to improve the distribution of daylight in rooms. Equations for the deflection angle and amount of light deflected are derived and related to applications of the material for daylighting and for sunlight exclusion. Measured performance of the material in the daylighting application is obtained, in model rooms, for a wide range of sky conditions. The material is most effective as a hung or tilted window in direct sunlight, however improvement in interior illumination with the window vertical and in overcast conditions is also significant.

Daylighting high-density residential buildings with light redirecting panels

This paper describes the use of light redirecting panels to improve the daylighting inside highly obstructed rooms at the lower levels of high-density residential developments in dense cities such as Hong Kong. Light redirecting panels are described and a simple design rule for the application of panels to highly obstructed windows, panel tilt angle-one half the obstruction angle, is derived. Scale model measurements demonstrate redirecting panels improve daylight factors by up to three times before discomfort glare becomes a limitation. Average ratio of daylight factors is a more useful measure of improved daylighting than the conventionally used average daylight factor.

Transmission of light through right-angle corners in hollow light guides

Transmission of light through the corners in hollow light guides is compared for a new type of corner that is based on a laser-cut light-deflecting panel and for a flat, 45°, mirror-type corner. Corner efficiency is defined, and an experimental method for the measurement of the corner efficiency versus the angular width of the input light is described. Measured corner efficiencies were found to be nearly independent of the angular width of the incident light for metallic hollow light guides, with the average efficiency of the laser-cut-panel corner (65%) lower than that of the mirror corner (80%).

Photovoltaic cells for low energy X-ray dosimetry

Selecting a detector for dosimetry three important factors are sensitivity, energy independence and convenience. Silicon solar cells have high volume sensitivity in the low-energy range associated with mammography, however, the sensitivity becomes dose dependent at low- dose rates. The dose rate dependence of sensitivity appears to be common to all silicon photodiodes but different types exhibit it to different degrees. Fortunately, it is possible to select photodiodes, the dose rate dependence of which is not significant at the levels of exposure encountered in routine mammography. In the energy range 10-50 keV silicon photodiodes with thin detection volumes are relatively energy independent and are well suited for mammography. Silicon photodiodes are much less suitable for general radiographic dosimetry due to the large variation in sensitivity which occurs from 50 keV upwards.

Time and injection rate dependence of minority‐carrier diffusion length in solar cells irradiated with x rays

The minority‐electron diffusion length in commercial n+p silicon solar cells was determined from measurements of transient photocurrent generated by low‐energy x rays. The results show an order of magnitude increase in diffusion length over a time interval inversely proportional to the square of the injection rate. This accounts for the occurrence of dose rate sensitivity of silicon detectors of x rays at very low injection rates. The strong rate dependence observed suggests a space‐charge trapping mechanism.