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A deep insight into surgical lighting

The right surgical lighting is critical for patient safety and staff comfort. It should be designed to enable the medical team to focus exclusively on the surgical operation.

Learn how to identify lighting that offers long-term benefits for your surgical suite.

What is important in a surgical light?

Successful illumination requires a special balance of luminance, shadow management, volume, and temperature. This maximizes visibility at the surgical site while minimizing eye fatigue.

History

Prior to the invention of the electric light, the first surgical operations took place in daylight, with illumination from 10,000 lx to 80,000 lx depending on the time of day and cloud cover.  By the end of the 19th century, light bulbs replaced direct sunlight and allowed more freedom to perform surgery throughout the day. By the 1960s, the use of halogen bulbs increased the amount of light available on the operating table to 100,000 lx — comparable to bright noon sunlight on a Mediterranean beach. Thirty years later, discharge lamps nearly doubled the available light to 200,000 lx! But this “more is better” approach led to eye fatigue, diminishing surgeons’ effectiveness. Today, more and more surgical lights operate with LEDs. These bulbs use less energy to produce crisper, cooler illumination that gives surgeons the visibility they need to make effective diagnostic decisions.

Illumination

Proper illumination is a compromise to ensure a good visibility with minimal glare and prevent eye strain for surgeons.

Maximum central illumination (Ec) must be between 40,000 and 160,000 lx at the center of the light patch, one meter from the light source.

Light patch size can vary depending on the type of surgery to limit peripheral glare. This light patch is calculated where illumination is greater than or equal to 10% of the maximum illumination (EC). The diameter of this area is known as D10.

Illumination must be uniform to reduce glare-related eye strain. The diameter will be measured where illumination is 50% of the Ec (called D50), and a D50/D10 ratio will be given. The standard indicates that this ratio must not be under 0.5.

Shadow Management

What is really important in term of shadow management is the useful light the surgical team will have when operating below the lighthead and not the power of the lighthead alone.

The quality of a surgical light depends on the amount of useful light found inside the cavity. This is a balance between the amount of light, and the ability to manage shadows.

There are two types of shadows: cast shadows and contour shadows. Cast shadows interfere with visibility, while contour shadows help us to gauge depth and volume. Effective lighting minimizes cast shadows while enhancing contour.

Cast shadows are influenced by the surface of the light source, how light is guided towards the operating field, where it’s most needed, and the number of light sources. More light beams improve shadow dilution, improving visibility for the surgeon.

Volume of light

Because the surgical cavity isn’t flat, surgeons need illumination in three dimensions. Merging several light patches —shining at the same time and strength at different heights — creates a uniform volume of light.

Volume of light is measured by an IEC standard equation: L1 + L2.

  • L1 is the distance between Ec and the point where luminance is measured at 60% going towards the lighthead
  • L2 is the distance between Ec and the point where luminance is measured at 60% going away from the lighthead

The best surgical light will have the highest volume of light at the cavity, even when the light is positioned more than one meter from the surgical site.
L2 measurement is particularly critical for deep cavity applications.

Heat Management

Light will be always energy so in order to prevent from tissue desiccation, a safe heat management is mandatory.

Heat can be measured in two places: at the light patch, and at the lighthead. Heat can cause discomfort for the surgeon, and can dry exposed patient tissue.

While LEDs do not produce damaging infrared rays, some heat remains. The more illumination, the more radiant energy. The IEC limits this irradiance to no more than 1000W/m2 at the light patch. Overlapping light patchs is always under surgeons’ control.

But lightheads are also a source of radiant heat, which needs to be reduced to prevent overheating and laminar flow disturbances.

A quality surgical light will minimize heat to improve comfort and patient outcomes.

Fail safe surgical lighting

There is no room for error in the surgical suite. Fail-safe equipment is designed to ensure that even in a single fault condition no safety hazard exists. It ensures that illumination and maneuverability are preserved, providing central illuminance of not less than 40,000 lx.

Single luminaries without any protection against light interruption under a single fault condition are not fail safe. A light with two minor luminaries with separate transformers, fuses, wiring, and slip rings would be fail safe.

Examples of single fault condition:

  • Breakage of wire inside the equipment
  • Failure of slip ring, or a fuse, or a lamp, or insulation
  • Failure in electronic device
  • Lamp power supply cables detachment

Dedicated standard for surgical lighting

International Electro technical Commission  (IEC) Standard 60601-2-41

The French company ALM initiated an international working group (Germany (Heraeus - Berchtold), UK (Brandon), USA (Steris - Getinge), Japan (Yamada), USSR, France (ALM + Angenieux) which was set up in 1990 on the basis of a French project. All the manufacturing partners finally reached an agreement in 1997. The submission to vote, publication and application starting in December 1999. This standard concerns the safety of surgical lights and examination lights. The worldwide organization for standardization comprising all national electro technical committees. Its objective is to promote international cooperation on all questions concerning standardization. The documents produced are presented as recommendations for international use. IEC national committees undertake to apply IEC International standards transparently to the widest extent in their national and regional standards. Any divergence shall be clearly indicated. IEC provides no marking procedure to indicate its approval. IEC does not accept responsibility for any equipment declared to be in conformity with one of its standards.

Today, the following companies attend to the IEC:

Steris (US), Getinge (Sweden), Berchtold/Stryker (Germany or US), KLS Martin (Germany), Rimsa (Italy), Brandon (UK), Draeger (Germany), Skylux (Japan)*

 

*as at November 2017