The physics of light distribution in hollow structures

The purpose of this paper is to serve as an introduction, for non-physicists, to the subject of light distribution in hollow structures. The motivation for light distribution is the importance of getting the maximum value from available light. We all recognize that photons cost money (one photon costs about $10(exp -25) to make) so we obviously want to try to make the maximum number of photons for a given cost. What is often overlooked, however, is that these photons have the highest value only if they are delivered to the right place in the correct quantity. This means that there is often substantial economic value in the high quality distribution of light. This problem is discussed from a very general perspective, in order to show the role of general optical films for manipulating light. The underlying physics at work in such films is described, and examples of common optical light distribution films are provided

Core Sunlighting System, a New Approach to Daylighting in Buildings

AbstractThe building industry recognizes the importance of incorporating daylighting into the illumination of buildings to improve energy performance and lighting quality. There are several well-known methods that building designers use to increase the daylighting level in buildings, including windows and skylights. However, these methods are usually not capable of illuminating the core of the building, and may increase the energy usage of the building due to reduced insulation. There are other systems designed for illuminating the core of buildings with daylighting, but all have some limitations that have impeded widespread adoption.An alternate daylighting system described here offers a novel approach to illuminating the core of buildings. This system consists of active and passive optical components that capture sunlight outside multi-floor buildings and transfer it to the dark core. Active sunlight redirectors, mounted at roof level on the edge of the building, track the sun throughout the day and redirect the sunlight towards building façades at a certain angle. Passive concentrator elements mounted on the façades of the building capture and concentrate the light and direct it into light guides. The sunlight is then distributed within the building via interior light guides to efficiently illuminate the building

Lighting Quality Evaluations using Images on a High Dynamic Range Display

Limited research comparing participant ratings of luminous environments to ratings of images of those environments indicates that images can be a reasonable surrogate for the real space, particularly on ratings related to aesthetics. However, the realism of such images when presented on computer screens is potentially limited by conventional display technologies that cannot reproduce the full range of luminances in real spaces. In this pilot experiment we used a new, high dynamic range (HDR) computer monitor capable of producing screen luminances and contrasts comparable to those in a real space. Fifty-four participants viewed three images of a conventional office in two display modes: HDR monitor and conventional monitor. Participants rated each image for room appearance, environmental satisfaction and realism. These ratings were also compared to similar ratings made by participants in an earlier experiment (reported in 1998) who occupied the real spaces depicted in the images. Results indicate that computer screen images are perceived in a similar way as real luminous environments. HDR images are perceived differently than images on a conventional monitor: they are rated as brighter and less attractive, as expected. Given their more authentic luminances, HDR images should be perceived as more similar to the real space, but our results neither support nor refute this

When it comes to teaching, is there a universal law that you cannot save time or use it differently?

This blog post is about teaching, and time, a topic that we briefly discussed during one of our ASCN Working Group 2 meetings.Science, Faculty ofNon UBCPhysics and Astronomy, Department ofUnreviewedFacult

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A simple principled approach for modeling and understanding uniform color metrics

An important goal in characterizing human color vision is to order color percepts in a way that captures their similarities and differences. This has resulted in the continuing evolution of “uniform color spaces,” in which the distances within the space represent the perceptual differences between the stimuli. While these metrics are now very successful in predicting how color percepts are scaled, they do so in largely empirical, ad hoc ways, with limited reference to actual mechanisms of color vision. In this article our aim is to instead begin with general and plausible assumptions about color coding, and then develop a model of color appearance that explicitly incorporates them. We show that many of the features of empirically defined color order systems (those of Munsell, Pantone, NCS, and others) as well as many of the basic phenomena of color perception, emerge naturally from fairly simple principles of color information encoding in the visual system and how it can be optimized for the spectral characteristics of the environment.status: publishe

High color rendering can enable better vision without requiring more power

For many people, the correct perception of the colors of objects is an important part of life, and today it is being threatened by misinformed policy-making and associated business decisions. Some conservationists and lamp manufacturers have concluded that the accurate color rendering provided by ordinary incandescent lamps is an unaffordable luxury that good citizens should forgo as we employ more energy-efficient alternatives. Though this is not as extreme as suggesting that we should live in cold darkness, it is in the same general direction of deprivation. Yet research has shown that color rendering is important to people and highefficiency lamps can now also provide high color rendering, so there is no longer any need to have lighting that distorts color appearance. This article focuses on the tradeoff between color rendering accuracy and lamp efficiency to show that high color rendering accuracy is appropriate and, contrary to a common misconception, does not intrinsically require greater electrical energy consumption.Peer reviewed: YesNRC publication: Ye

Chromaticity-matched but spectrally different light source effects on simple and complex color judgments

As light-emitting diode (LED) light sources mature, lighting designers will be able to deliver white light with a variety of spectral power distributions and a variety of color rendering properties. This experiment examined the effects of three spectral power distributions (SPDs) that were matched in illuminance and chromaticity on three measures of color perception: one objective (performance on the Farnsworth-Munsell 100 hue test) and two subjective (judgments of the attractiveness of one's own skin, and preferences for the saturation of printed images). The three SPDs were a quartz-halogen (QH) lamp and two LED sources that were matched to the QH lamp in terms of both illuminance and chromaticity; the three light sources were nominally CCT = 3500 K, x = 0.40, y = 0.39 and 3c 400 lx. LED A used three channels (red, green, blue), and had very poor color rendering (Ra = 18). LED B used four channels (red, amber, cyan, white) and had very good color rendering (R a = 96, whereas the QH had Ra = 98). Secondary hypotheses addressed the effects of age and skin and eye color on the dependent measures. As expected, LED A delivered very different color perceptions on all measures when compared to QH; LED B did not differ from QH. The results show that it is possible for LED sources to match the familiar incandescent sources. However, although it is possible to deliver what appear to be millions of colors with a three-chip (RGB) device, there is the risk of creating a very poor luminous environment. \ua9 2013 National Research Council Canada and Wiley Periodicals, Inc.Peer reviewed: YesNRC publication: Ye