of obstructions. Light field diameter (D10) Diameter of light field around the light field centre, ending where the illuminance reaches 10% of Ec. The value reported is the average of four different cross sections through the light field centre. D50 Diameter of light field around the light field centre, ending where the illuminance reaches 50% of Ec. The value reported is the average of four different cross sections through the light field centre Norms and requirements for surgical light The International Electrotechnical Commission (IEC) created the document IEC 60601-2-41 – Particular requirements for the basic safety and essential performance of surgical luminaires and luminaires for diagnosis, 2009 to establish norms and guidelines for the characteristics of a surgical and examination light to secure safety for the patient as well as lower the risk to a reasonable level when the light is used according to the user manual. Some of the standards for surgical lightheads are the following: Homogeneous light: The light should offer good illumination on a flat, narrow or deep surface in a cavity, despite obstacles such as surgeons' heads or hands. Lux: The central illuminance should be between 160,000 and 40,000 lux. Light field diameter: The D50 diameter should be at least 50% of D10. Colour rendition: For the purpose of distinguishing true tissue colour in a cavity, the colour rendering index (Ra) should be between 85 and 100. Backup possibility: In case of interruption of the power supply, the light should be restored within 5 seconds with at least 50% of the previous lux intensity, but not less than 40,000 lux. Within 40 seconds the light should be completely restored to the original brightness. Announcement: The IEC document also mentions what needs to be notified to the user. For example, the voltage and power consumption should be marked on or near the lampholder as well as on the lighthead. In the instructions for use the following should be announced. Cleaning and decontamination of the surgical light Safety aspects of the optical filter (purpose and warning to prevent removal) Central illuminance Light field diameter Depth of illumination Shadow dilution Correlated colour temperature and colour rendering index Total irradiance Cleaning and disinfecting Handling of the lighthead in case of failure How the user should respect the national rules for hygiene and disinfecting References Extrait de la revue Techniques Hospitalières noo 400 Janvier/1979 "L’éclairage en salle d’opération" by M. Hainault