VISIBLE LIGHT, LYING BETWEEN INFRA-RED AND ULTRA-VIOLET, CONSTITUTES ONLY A VERY SMALL PART OF THE ELECTROMAGNETIC SPECTRUM. THE PERCEPTION OF COLOUR IS A FUNCTION OF WAVELENGTH AND THE HUMAN EYE IS NOT EQUALLY SENSITIVE TO ALL WAVELENGTHS. LUMINOUS FLUX REPRESENTS THE VISUALLY EFFECTIVE VALUE OF THE LIGHT. A TERM ORIGINATING IN THE EIGHTEENTH CENTURY AND BASED ON THE OUTPUT OF A STANDARD CANDLE IS THE CANDELA. THE LUMINOUS FLUX FROM A LIGHT SOURCE WITH AN INTENSITY OF ONE CANDELA, WHEN PASSING THROUGH ONE SQUARE METRE AT A DISTANCE OF ONE METRE, IS CALLED A LUMEN. ONE LUMEN DISTRIBUTED OVER AN AREA OF ONE SQUARE METER GIVES AN ILLUMINANCE OF ONE LUX.
THE HUMAN EYE IS VERY ADAPTABLE. IN MOONLIGHT AT 0,5 LUX, OR UNDER A STREET LAMP AT 5,0 LUX, A MAN MIGHT BE ABLE TO READ A LETTER AND YET STILL BE ABLE TO READ IT AT 50 000 LUX ON A SUNNY DAY. HOWEVER, IF HE WERE ABLE TO TAKE THAT LETTER IMMEDIATELY FROM SUNLIGHT TO MOONLIGHT, HIS ABILITY TO READ THE LETTER WOULD BE IMPAIRED UNTIL HIS EYES HAD ACCLIMATIZED. THIS SITUATION CAN BE CREATED BY ARTIFICIAL LIGHTING AND INDICATES THE IMPORTANCE OF THE EVEN DISTRIBUTION OF LIGHTING FOR SAFETY WHEN PERSONS MIGRATE FROM ONE WORK AREA TO ANOTHER.
FROM AN ARCHITECTURAL POINT OF VIEW, IT MAY BE NECESSARY TO STRIKE A BALANCE BETWEEN THE AESTHETIC AND ECONOMIC ATTRACTIONS OF DRAMATIC LOCAL LIGHTING, WITH IT’S INHERENT RISK OF GLARE, AND THE SAFER, BUT PERHAPS UNINSPIRING, UNIFORM LIGHT LEVELS.
A HAZARD FOR THOSE WORKING WITH ROTATING MACHINERY IS THE RISK THAT A STROBOSCOPIC EFFECT FROM AN UNSTABLE LIGHT SOURCE MIGHT CAUSE A CATASTROPHIC MISJUDGEMENT BY THE OPERATOR.
THE MOS ACT, NOW INCORPORATED IN THE OHS ACT, SPECIFIES THE MINIMUM LUX LEVELS FOR MOST WORKING ENVIRONMENTS BUT THESE VALUES ARE THE MINIMUM LEVELS FOR SAFE WORKING AND THE LEVELS FOR OPTIMUM PRODUCTIVITY MAY BE CONSIDERABLY HIGHER.
WITH THE EASY TO READ TM-202 DIGITAL LUX METER, RUNRITE, THE KWA-ZULU NATAL BASED SUPPLIERS OF ENVIRONMENTAL TEST INSTRUMENTS OFFER A COST-EFFECTIVE SOLUTION FOR PRELIMINARY ILLUMINATION SURVEYS.
Wednesday, June 3, 2009
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