It is critical that Surgeons have access to good lighting when performing surgical procedures. Most commonly Surgeons ask for adequate illumination of the surgical site (including deep cavities), minimal heating of the surgical site, helpful colour that renders tissue in a familiar way, convenient positioning of the light head and convenient control of the lighting systems features.
What is Illuminance?
Illumination is a term used to describe the provision of light to enable vision. The term illuminance however is used to quantify how much light is actually available. Illuminance is therefore calculated as the amount of visible light that strikes a surface, divided by the area of that surface. The amount of light available is then measured in lumens. A common unit of Illuminance is lux (which is one lumen per square meter) or footcandles (which is one lumen per square foot). The human eye is able to respond to a wide range of Illuminance. Typically the lighting conditions in an everyday life, hospitals and operating theatres are as follows:
| Lighting Conditions | Typical Illuminance |
| Thresh hold of seeing | 1 lux |
| Professional office | 500 lux |
| Examination room (emergency department) | 1000 lux |
| Operating room (general room lighting) | 9300 lux |
| Surgical lighting | 40 000-160 000 lux |
Surgical site Illumination
Very high levels of Illuminance are needed when performing surgery. This is necessary for two reasons:
- Often there is partial obstruction of the light beam due to the heads and shoulders of the surgical team
- It is difficult to deliver light into cavities of the body, especially as there are multiple reflections from the side walls
As a result surgical lights are designed to deliver high amounts of illuminance. Most surgical lights can be adjusted to deliver the amount of light output required when operating on specific parts of the human anatomy.