LIGHTING
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GUE FATI EYE ACHE HEAD IRRITABILITY STRESS When equipping a Dental Surgery, technical, ergonomic and cost factors all come into play. Such factors are taken into consideration when choosing, say, an arm unit or furniture, but sometimes disregarded when deciding on a main overhead light, despite the fact that light is just as essential in the surgery as it is to life itself. Appropriate lighting improves work performance by reducing tiredness and stress. Eye fatigue, headache and nervous tension (which are detrimental to interpersonal relations hence to mood towards the patient) also reduce visual capacity over time and are often caused by an improperly lit work environment. The correct values for interior artificial lighting are set by Regulations. Some examples: Offices 200 - 750 lux; Homes 150-500 lux. If such values are adopted in a Dental Surgery, however, the environment would not be properly illuminated. Why? A unit arm lamp emits 18,000 to 22,000 lux at a distance of one metre. The light, however, is focused, so in the immediate vicinity the percentage of light falls below the lux value required for comfortable vision leading to eye strain and rapid fatigue (similar to that experienced by drivers emerging from a tunnel into strong sunlight who are momentarily dazzled until their eyes adapt). A team of German dentists and lighting technicians has developed Standard DIN 67505 which sets out the quantity, quality and distribution of light for dental studios at 1600-2400 lux around the mouth, 1000 lux in the work area and 500 lux for general ambient lighting. How are these values obtained? Light propagation is inversely proportional to distance: 1000 lux at one metre from the light source becomes 250 lux at 2 metres; therefore, a main overhead light attached directly to the ceiling (fig. 1) is too far from the work surface (in these conditions, a good main overhead light with four 58 W tubes would provide only about 400 lux.). While the same light suspended at 2.20 m above floor level would provide the required lux value, suspended conventional main overhead lights inevitably create distinct areas of shade on the ceiling and walls (fig. 2) and the contrast between light and shade is a source of eye fatigue. Correct diffusion of light can be obtained using a bidirectional main overhead light (fig. 3). The quality of light is prescribed at 5400 K and indications are provided both for the percentages of blue, red and yellow that, when mixed, combine to form daylight as well as for the minimum chromatic yield index (IRC) for better colour perception. A final feature necessary to provide illumination in the Dental Surgery that is as faithful as possible to natural light is electronically supply (controlled ignition). Fig.1 Traditional installation on ceiling. Unlighted walls and ceiling, light/dark contrast with consequential sight fatigue for operator. Fig.2 Hanging installation. Improves the light intensity over unit, but increases the light/dark contrast, therefore also causing fatigue. Fig.3 LUCIE - ELENE: multidirectional lighting and electronic power. Diffused lighting, elimination of contrasts. Reasonable cost.

Electronically supply (controlled ignition) is a very interesting alternative to traditional 50 Hz frequency systems. In the traditional system, the gas in the fluorescent tube receives 50 pulses per second and the light is continuously switched on and off and perceived by the eye to flicker. If the micromotor operates at a low number of revolutions, a stroboscopic effect is created causing rotating instruments to appear still or to jerk leading to dangerous optical illusions that cause eye fatigue after long working hours. With electronically supply (controlled ignition), the frequency is...