Light and UV

Lux measuring devices are often very difficult to compare in terms of their quality. The accuracy is often only given for certain test criteria (e.g. incandescent light, certain angle, etc.), with each manufacturer specifying different criteria. The only reliable proof of quality is the classification according to DIN 5032 part 7, whereby 16 criteria are examined. For class B, the total error calculated according to a certain formula is max. 10%, with class C at max. 20%. A maximum value applies to each of the 16 test criteria.

Another question is what accuracy is required in the museum. As explained on the didactic side (only in German so far), the measurement of the illuminance (lx) gives only very limited information about the damage potential of the light. The question of what proportion of blue light contains is at least as important. The UV component is also not taken into account in the lux measurement. A UV measuring device is therefore ultimately indispensable when it comes to minimizing light damage. In the literature, accuracy class B is sought as for museums. For the reasons mentioned above, however, it can be asked whether high accuracy is always the decisive factor when measuring lux in museums. However, lux measuring devices should certainly not be completely inaccurate, not least so that the measurements between the individual museums and with different devices remain comparable. Ultimately, each user must choose the best solution for him- or herself.