Natural DayLight-mediated PhotoDynamic Therapy (NDL-PDT) is an efficacious treatment option for thin actinic keratosis that offers advantages over conventional PDT in terms of tolerability and cost. It is now accepted that the minimum criteria required for effective NDL-PDT is a dose of 4 J/cm² with a treatment time of 2 hours and a minimum temperature of 10 °C, corresponding to a minimum illuminance of 11,000 lux. This value is easily achievable: 20,000 lux can be obtained during a typical overcast day at midday. It can reach 110,000 lux with a bright sunlight. However, it is limited to certain times of the year at our latitude. However rain and cold temperatures appear the main limitations of NDL-PDT. Greenhouses make possible to perform the illumination even in harsh weather conditions. Furthermore, it is difficult to install a greenhouse everywhere. Several solutions are now proposed to carry out indoor illumination so-called artificial white light or simulated daylight (SDL-PDT). Illumination sources installed at the ceiling of the treatment room is one option. Several lamp pairs can be combined to illuminate groups of patients simultaneously. A surgical theatre light can be used or dedicated systems using white LEDs can be used to deliver the required illumination dose. In conclusion, Indoor lightning (or simulated daylight: SDL-PDT or Artificial White Light: AWL) could offer an interesting alternative to NDL-PDT.