Parameters influencing the accuracy and practical applicability of UV indicator cards

Recently, inexpensive UV indicator cards that change their colour depending upton the level of UV irradiance and often referred to as ´suncheck cards´ have become commercially available. These could be a valuable tool to indicate appropriate protective measures both of outdoor workers as well as for ´private´ use (according to the prosposed EU directive on optical radiation (1) employers have to assure that their workers are protected from harmful levels of UV radiation at the workplace, although regulation regarding solar UV by this directive is still under discussion). The tested UV indicator cards are credit card sized (86 x 54 mm) and are made out of cardboard. A test field on the cards alters its colour (in a reversible way) depending upon the momentary irradiance level of UV radiation incident upon the indicator field. Ideally, the change of colour should be related to the erythermally weighted effective irradiance should result in a pale colour of the indicator field, while a high effective irradiance should lead to the appearance of a dark colour in the indicator field. For the application of the cards, the colour change of the indicator field has to be compared to the colour of printed reference fields which are generally associated to advice concerning personal protection against solar UV radiation such as to apply sunscreens with a certain SPF (sun protection factor) or to seek shade. The number of reference fields per card varies from three to four. The appearance of one of the tested UV indicator cards is shown in Fig.1. The colour change of the cards is reversible. If the UV exposure of the cards is paused, the colour change of the indicator field turns back to its original greyish-white colour. In total, five different types of reversible UV indicator cards were examined.