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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®standards | OPTICAL SAFETYLED-based products must meetphotobiological safety standards: part 2The potentially complex procedure of evaluating LED photobiological safety is now a legalrequirement in Europe, but few countries have yet followed the European mandatory-testing lead.LESLIE LYONS discusses the implementation of the IEC62471 standard after an in-depth look at themeasurement of radiance and irradiance.Part one of this three-part series providedan overview of the potentialhazards to the human body posed byexposure to optical radiation, and the developmentof international standards to evaluatethe photobiological safety of non-lasersources (see LEDs Magazine October 2011,p31; ledsmagazine.com/features/8/10/8).Here, a more practical approach is adopted,in considering the finer details of source evaluationand the implementation of safety standardsin Europe and the rest of the world.Scope of IEC62471:2006The IEC62471:2006 standard “PhotobiologicalSafety of Lamps and Lamp Systems” providesguidance for the evaluation of the photobiologicalsafety of all electrically-powered,non-laser sources of optical radiationemitting in the spectral range 200-3000 nm,whether or not the emission of light is theprimary purpose of the product. The inclusionof LEDs in the scope of this standardis specifically mentioned to highlight theremoval of LEDs from the scope of the laserstandard, IEC60825.The potential hazards of exposure to theskin, the front surfaces of the eye (cornea,conjunctiva and lens) and the retina areevaluated through consideration of six specifichazards with respect to exposure limits(ELs) provided for an exposure durationof eight hours, taken as a working day. TheLESLIE LYONS is the Technical SupportManager with Bentham Instruments Ltd (www. ____________bentham.co.uk), Reading, UK. He is a member ofBSI and IEC committees including TC76, OpticalRadiation Safety and Laser Equipment.standard does notconsider the potentialeffects of longtermexposure,nor of abnormalphotosensitivity.In the case ofhazards to theskin and front surfacesof the eye,it is sufficient to FIG. 1. Defi nition of irradiance.take into accountthe amount of lightincident on the surfacein question.However, to considerhazards to thedAretina, one musttake account of theimaging propertiesof the eye. It followsthat two distinct FIG. 2. Defi nition of radiance.measurements arerequired: irradiance and radiance.The standard provides specific guidanceon the geometrical conditions under whichthese measurements should be made to takeinto account biophysical phenomena, such asthe effect of eye movements on retinal irradiation.The spectral range over which radianceshould be considered is reduced to 300-1400nm, since the retina is essentially protectedoutside this range due to the transmissioncharacteristics of the lens. Table 1 indicatesthe required measurement (radiance or irradiance)for different hazards.Measurement of irradianceIrradiance permits the evaluation of hazardsdΩθdϕdϕdAto the skin and front surfaces of the eye.Irradiance is defined as the ratio of radiantpower (dΦ) incident on an element of a surface,to the area (dA) of that element (Fig. 1).Its symbol is E and its units are W/m².Irradiance accounts for light arriving ata surface from the entire hemisphere above.However, due to its position with respect tothe bridge and nose, the eye is shielded fromwide-angle radiation. Within the scope ofthis standard, the measurement of irradiancein all but the case of the thermalskin hazard is performed over a 1.4-radianacceptance angle. Light emitted from asource outside this acceptance angle neednot be measured.LEDsmagazine.com NOVEMBER/DECEMBER 2011 65Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM qMM MQmags| Next Page q qTHE WORLD’S NEWSSTAND ®