New standards for safe lighting
The fast-growing significance of state-of-the-art solid state lighting (SSL) light sources in the living and working environment raises important questions with regard to safety. These include photobiological safety, and in particular blue light hazard (BLH). Blue light can cause photochemical damage to the retina, and may result in degeneration of the macula.
The BLH weighting function covers the wavelength range between 300 and 700 nm, and has a maximum at 435–440 nm. In view of the striking blue peaks of white LEDs, the question of hazard from SSL light sources must be posed.
The challenge: Determination of BLH risk classes pursuant to standard IEC 62471
International Standard IEC 62471 sets forth guidelines for assessing the photobiological safety of lamps and luminaires. It places stringent requirements on measuring equipment and processes, to ensure reliable assessment of photobiological hazards and the correct subdivision into BLH risk classes for light sources. Depending on the weighted radiance and exposure times, IEC 62471 classifies light sources into four risk groups from 0 (exempt) to 3 (high risk).
In addition, Technical Report IEC-TR 62778 explains how IEC 62741 can be used for simple assessment of the blue light hazard of lamps and luminaires with visible radiation. Currently, efforts are underway worldwide to develop this technical report into a new standard and to add detailed measuring procedures for BLH assessment that are accessible to a broader community. Instrument Systems is actively supporting these efforts.
Array spectroradiometer with stray light correction
For correct risk assessment it is important to have a suitable measuring system. Today an array spectrometer is often the measuring instrument of choice, instead of the difficult-to-handle double monochromator proposed by the original Standard IEC 62471.
But even high-end array spectrometers must have a procedure for stray light correction in order to achieve the required high optical dynamics, particularly in the less sensitive blue region. Carefully conceived test adapters are necessary to ensure correct and reproducible test geometry. With such instruments, test labs accredited according to ISO 17025 can reliably assign lighting products to risk classes.
Two main procedures for BLH assessment were suggested in IEC 62471: direct spectral radiance measurement and an alternative procedure as irradiance measurement with a precisely defined field of view. In this case, the measured irradiance is divided by the solid angle to obtain the radiance value.
Our solution: BLH assessment of SSL light sources with systems from Instrument Systems
Instrument Systems offers high-end spectroradiometers and accessories for sensitive and fast measurements in the lab and production. Direct spectral radiance measurement from 360 nm can be performed with a TOP telescopic optical probe in combination with a CAS140D array spectrometer calibrated to the spectral radiance.
Our alternative method for the determination of blue light hazard consists of a stray light-corrected array spectrometer with a PTFE integrating sphere calibrated to irradiance, and a tube that has the necessary apertures for calculating radiance. This system covers the entire spectral range of the BLH weighting function from 300 to 700 nm.
The systems for measuring blue light hazard from Instrument Systems are tested by our test lab accredited to ISO 17025. The results, in particular metrological traceability, are confirmed by an enclosed DaKKS test report. The equipment can thus be used directly by test labs for testing in the accredited scope of ISO 17025 and other international standards.
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