Evaluation of Illumination Glare Good Illumination

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16.4.2 Evaluation of Illumination

The instrument most commonly used for the measurement of illumination is a photoelectric light meter often termed a Lux meter. When light is incident upon the photoelectric cell, the energy in the radiation is converted into electrical energy and the current produced recorded on a meter calibrated in lux. It has a built-in filter which automatically applies the necessary correction factor when daylight, mercury lamp light or fluorescent light is to be measured, and is colour corrected to respond to the human eye. The quantitative results obtained are assessed in terms of appropriate guidance criteria such as those recommended by CIBSE or ASHRAE.

16.4.3 Glare

Glare may be defined as any brightness within the field of vision where such character would cause discomfort, annoyance, interference with vision, or eye fatigue. Three different types of glare may be present separately or in combination. Disability glare this will affect the capacity to see clearly, e.g. the undipped headlamp on a car or sunshine reflecting from a wet surface. Discomfort glare this effect increases with time, e.g. a part of a visual scene windows by day, lighting by night may be too bright compared to the background. Reflected glare this is seen in shining or polished surfaces which reflect a more or less distorted image of a bright light, fitting or window. This can be annoying or disabling, for it may be difficult or impossible to see whatever is beneath.

16.4.4 Good Illumination

General guidelines for designing illumination of sufficient quantity and suitable quality are:  Consider lighting at the design stage of any building or workplace 157  Design for sufficient lighting levels in line with established guidance such as the CIBSE code‟  Integrate daylight and artificial light  Avoid glare  Minimise flicker  Ensure adequate maintenance of glazing surfaces and light fittings. 158 17 IONISING RADIATION

17.1 Nature