Diadem bulbs are coated with a special opalescent surface that shines in a silvery fashion, even when inactive. Only during signal operation, for instance when flashing, does the lamp light up with its characteristic yellowish-orange colour.
The advantages of diadem bulbs are their higher intensity and longer service compared to conventional bulbs. In addition, the silvery-white surface barely contrasts with the rest of the headlight, thus improving the overall look for modern, clear-glass headlights in particular.
Diadem bulbs are approved for use throughout Europe.