Optical radiation, including light from artificial sources, may cause so-called photobiological hazards to the eye and skin. This is a problem widely discussed in the lighting industry, which leads to many misunderstandings and doubts. These may result, on the one hand, from the fact that the assessment of these hazards requires specialist knowledge and experience, and, on the other hand, the regulations specifying the method of measurement and classification of sources included in the EN 62471 standard have been described in such a complex way that the interpretation of the standard’s recommendations causes many problems for practically all participants of the lighting market. Additionally, various and often extreme positions as to whether each manufacturer and marketer should measure their products or not, provide further doubts.
published by Miko Przybyla and Tomasz Pawlicki in LED Lighting Magazine
It is worth noting that in the case of light-emitting diodes (LEDs) due to the lack of emitted infrared radiation, the spectral measurement range can be narrowed down to the range from 200nm to about 800nm. However, it should be remembered that even visible radiation, especially blue light hazard, depends not only on the light source used, but also on the design of the lighting product. The use of different optics in luminaires and lamps – lenses and other components – affects the luminance level, so manufacturers should verify or commission appropriate laboratories to assess the photobiological risk of lamps and lighting systems.
Complete system solution
In order to provide a complete solution to improve complex measurement methods and ensure accurate measurement, GL Optic has developed a measurement system consisting of a high resolution, calibrated spectroradiometer with irradiance and radiance measuring optical probes, as well as analytical software for data interpretation and reporting. It is one of the few such solutions available in the world, because usually very complex laboratory measuring systems are used for this type of measurements, requiring very specialised metrology knowledge and using very expensive and difficult to use double monochromators.
The photobiological safety measurement system described in this article has been designed to meet the requirements of the EN 62471 standard and at the same time give the possibility of its use in factory laboratories of lamp and luminaire manufacturers, and not only in typical metrological laboratories. The hazards caused by optical radiation determine several aspects of the impact of this radiation on the human body, in particular the hazard to the eye and skin. In order to be able to define the levels of these interactions in an appropriate scientific way, the standard describes the method of their evaluation on the basis of known radiometric values, i.e. irradiance and radiance (radiometric equivalent of illuminance and luminance).
Hazards to the skin
For each type of photobiological interaction, the spectral efficacy of each interaction has been determined. The effective curve is taken into account in the measurement of the previously mentioned radiation radiometric values. In the case of the GL PSM System, the included analytical software ensures that the results are calculated properly and the operation is automatically handled by the software. The standard specifies under which conditions and which parameter should be measured in order to assess the type of photobiological hazard. Most of the risks described relate to the amount of energy in a given spectrum range reaching the human skin. Such conditions are directly reflected in the measurement of irradiance with the help of a cosine corrected measurement head. The kit offered by GL Optic includes a specially designed and manufactured irradiance head made of suitable materials.
Fig. 1. Irradiance measurement head operating in a wide range from 200 to 1050nm with class A cosine correction.
Hazard to the eye
A much more difficult task is to recreate the phenomena occurring in the human eye. The eye organ is at risk of excessive exposure to blue light. However, in this case we cannot simplify the procedures for measuring the intensity of irradiation on a flat surface. In the case of the eye, we are interested in the image of the observed object displayed on the surface of the retina. In such a system, measurements are complicated by several aspects related to the structure and work of the eye. Particularly dangerous conditions occur when the light coming from the observed object is focused by the lens of the eye and its focused sharp image falls on a certain part of the retina. The highest light intensity is recorded in the area where the image is focused, and therefore the study of the hazard of blue light focuses only on this small area of the retina. In addition, we take into account the movements of the eyeball, which in a certain period of time disperses the projection of the image onto a larger area of the retina. This mechanism in turn reduces the level of irradiance at a given point of the retina.
Fig. 2. The image of the light source displayed on the retina of the eye.
In relation to the phenomena described above, the standard defines the methodology of assessing the risk of blue light. The work of the human eye should be simulated with a system for luminance/radiance measured at precisely defined observation angles. One of these angles corresponds to the exposure in a very short time, when we eliminate the influence of eyeball motion. The second angle corresponds to the full range of such movements occurring naturally during a longer observation time.
The key element of the GL PSM System for measuring this hazard is a precisely designed telescope for measuring radaince at the two angles in question, i.e. 0.1 rad and 0.011 rad. An additional function of the telescope is the ability to illuminate the observation area of the device. This is very important and helpful in the measurement procedure specified in the standard. At each stage it is required to define the range of angular size of the observed object, which we can easily achieve by illuminating this place with the described tool.
Fig. 3. A telescope for the measurement of radiance at the two angles, i.e. 0.1 rad and 0.011 rad.
The optical measurement systems described above cooperate with the GL Spectis 5.0 Touch spectroradiometer, the parameters of which meet the high requirements of the above mentioned standard. If we also want to determine the thermal hazards resulting from the further infrared radiation range, GL Optic also offers the system including an InGaAs spectroradiometer.
The complex blue light hazard assessment process is coordinated by the tool contained in the GL Spectrosoft software. The step-by-step guide guides the user through the measurement procedure, asking questions and giving instructions to carry out the next steps based on the results obtained. After completion of the process, the software determines, among other things, the hazard group, maximum exposure time or minimum installation distance of a given product.
The use of appropriate measuring equipment, calibrated with the use of appropriate reference standards and correct interpretation of measurement data is helpful for the operator in the proper assessment of photobiological safety. However, it should be remembered that in addition to the equipment and its calibration, it is necessary to ensure appropriate laboratory conditions and to become familiar with the subject of risk assessment in order to carry out measurements and report the results according to the standard.
The optical measurement systems described above cooperate with the GL Spectis 5.0 Touch spectroradiometer, the parameters of which meet the high requirements of the above mentioned standard. If we also want to determine the thermal hazards resulting from the further infrared radiation range, GL Optic also offers the integration of the system with an InGaAs spectroradiometer.
If you are interested in learning more about specific instruments available from GL Optic please visit solution page here