Lighting : LIGHTING Apr-May 2018
22 LIGHTING MAGAZINE | April/May 2018 Tunnel lighting and the entrances to car parks are examples of where the impact of sunlight cannot be ignored. Whilst light-adaptation is very fast, compared with dark- adaptation, the visual system cannot respond sufficiently quickly to maintain contrast sensitivity when making a rapid transition from a sunlit exterior to indoor illuminances. Even at walking speeds, visual disability can result, however, when driving the effect is similar to temporary blindness. Thus, carpark entrances and tunnels require special electric lighting of the threshold zone between daylight and electric lighting. In the case of tunnels, the threshold zone can be very long and requires very high electric lighting luminances, which taper-off to the design luminance of the interior. SKYLIGHT As was mentioned above, the sky is illuminated by the sun either due to scatter by small particles (to produce the clear, blue sky) or larger water vapour (and pollution) particles (to produce cloudy or fully overcast skies). The sky can be thought of as a The luminance of the clear blue sky is low compared with the area lit. (http://meditately. com/wp-content/ uploads/2014/08/ clearsky.jpg) hemispherical vault centred on the point of interest. The sky is always above that point, whether it is on the ground floor or the fiftieth floor of a building. The clear (blue) sky This has a dynamic luminance distribution determined by solar motion. It has a relatively low luminance compared with the sun and, due to its bluish appearance, a much higher correlated colour temperature (up to 10,000K). It has an efficacy of around 150lmW-1 . The low luminance results in very strong modelling produced by the combination of the strong, directional sunlight and the softer diffuse skylight. The higher CCT results in the effect that it is “cool” in shaded areas and that the shadows produced are “cold” compared with the “warm” sunlit areas. The CIE Standard Clear Sky luminance model can be used for undertaking lighting calculations of instantaneous and average indoor illuminances and luminances. As with sunlight, design with the clear sky is difficult in that instantaneous values are not usually of great importance, rather, working-hours’ average available illuminances are usually needed to determine the sizes of windows and rooflights and in energy and control calculations. The (fully) overcast sky This has many cloud layers resulting in there being no indication of the solar position. The sky is common in northern Europe and has been extensively studied. The overcast sky is symmetrical about the zenith and varies in luminance with altitude. The CIE Standard Overcast Sky which has a luminance distribution which is symmetrical about the vertical through the zenith and is represented by the relationship Lθ = L z (1 + 2sinθ)/3, where Lq = luminance at an altitude θ above the horizon, and Lθ = zenith luminance (ie, at θ = 90°). The zenith luminance is three times that at the horizon and the average luminance, Lav is 7Lz/9. Since the sun is not evident with fully overcast skies, the overcast sky has a higher luminance than the clear sky often resulting in gloomy interiors unless electric lighting is also used, irrespective of the illuminances produced. You will be amazed by what is possible support your creativity The Pixalux® Structural Light Panel is a patented Australian lighting innovation that defines an entirely new category of lighting product- a panel of evenly distributed light that becomes the functioning structure itself. Use it as an illuminated shelf (providing beautiful, shadowless light), a floor, a cupboard wall or a door. Or try a point of sale stand with illuminated graphics and branding on one side, and product lighting on the other. It isn’t a case of adding illumination to your display stand, the stand itself illuminates. Elegant, simple and functional, Pixalux® Structural Light Panels will change the way you think about the application of light. Pixalux Design Pty Ltd Tel: +61 2 4257 8957 | email@example.com | www.pixalux.com.au 6 Fox Avenue,Wollongong NSW 2500, Australia Sunglass Hut Store ® Contact us to discuss your lighting idea; you will be amazed by what is possible.
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