Modern Solid State Lighting (SSL) technology has long since found its way into our normal working and living environments. In the early phases, consumers were most concerned with lifetime, pricing and light quality of the new LED-based light sources. Now they have become almost ubiquitous, a focus has been placed on safety. At the recent Light+Building exhibition topics such as photobiological safety and blue light hazard (BLH) were highly ranked among both visitors and exhibitors.
Photobiological safety is nothing exclusive to SSL sources, but must be evaluated for all light sources. Due to their similarity to laser diodes, LEDs were originally covered by the laser safety standard IEC 60825, which often led to an overestimation of the risks. Since 2009 LEDs and SSL sources have therefore been subject to IEC 62471 “Photobiological safety of lamps and lamp systems”. All lamp and luminaires brought onto the market must be classified according to this standard.
The standard identifies two health hazards that can be caused by visible light. Intense light may lead to retinal burns, a hazard that is easily avoided by normal aversive behavior. However, blue light between 400 nm and 500 nm may cause photochemical damage to the retina, a hazard that is difficult to assess by users. This so-called blue light hazard may lead to degeneration of the macula. The corresponding weighting function ranges from 300 nm to 700 nm with a maximum of 437 nm. In view of the distinctive blue peak of white LEDs, the question arises as to whether SSL sources are hazardous.
Depending on the radiance levels, BLH sensitivity and exposure times, IEC 62471 divides light sources into four risk groups ranging from 0 (no risk) to 3 (always dangerous). Risk groups 1 and 2 are sources that are not dangerous under normal behavior and aversion reactions. The standard also describes measurement equipment and procedures for the correct assessment of the risk classes of light sources. Additionally, IEC/TR 62778 explains how to apply IEC 62741 for simpler assessment of the BLH for lamps and luminaires.
Accurate risk assessment is a challenging task for the experimenter, and starts with the selection of the correct test equipment. Today’s measurement instrument of choice is often an array spectrometer instead of the hard-to-handle double monochromator suggested by the standard. But even high-end array spectrometers must offer advanced stray light correction methods to achieve the required high dynamic measuring range, especially in the less sensitive blue region. Carefully designed test adapters are necessary to ensure correct and reproducible test geometries. These equipment testing labs, which should be accredited to ISO17025, can reliably assess the risk class of lighting products.
Several studies have evaluated the risk classes of various kinds of SSL sources, lamps and luminaires. In general, SSL sources were not found to pose a greater risk to the user than conventional sources. Most luminaires with non-directly visible LEDs were assigned to risk class 0. Only luminaires with directly visible LEDs ended up in risk class 1 or, in some cases, in class 2, which the standard still classifies as free of risk under normal use and aversion reaction – just like conventional sources.
I must emphasize that these positive results should not encourage manufacturers to underestimate the importance of safety assessment of light sources. Research on the safety aspects of lighting will continue, and only accredited labs using state-of-the-art test equipment will be able to ensure a reliable risk assessment. Consumers may rightfully expect lamps and luminaires providing light that is safe in every aspect. Otherwise, SSL lighting will not be able to assert itself in the long term.
published in LED professional Review 3/2018