The acquisition of a surgical light essentially requires thorough understanding of the subject; that it is a critical medical device that determines often the outcome of a life saving surgical operation. The success of a surgical operation has a strong connection with the comfort, efficiency and focus of doctors and staff who are executing complex, tiring and long-drawn surgical operation. The performance of surgical light has profound influence on comforts, efficiency and focus of doctors and staff performing the surgery.
In order to enable the development of a quality surgical light, it is important to maintain a balance among luminance of the light, shadow management at the surgical site, volume of light available at the surgical site, thermal management of surgical light, colour temperature, quality of electro-mechanical components, the redundancy and serviceability.
The ideal illumination that enable good visibility with minimum eye strain to surgeons is of great importance when developing a surgical light.
Maximum Central Illumination (Ec) shall be in the range of 40000 to 160000 Lux at the centre of the Light Patch, at one meter from the Light Source.
Light patch size may vary depending on the type of surgery performed. The light patch is calculated where illumination is greater than or equal to 10% of the maximum illumination (EC). The diameter of the area is known as D10.
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. Illumination must be uniform to reduce glare-related eye strain.
Colour Temperature (3,000 – 6,700 K) is the measurement of the light source’s colour relative to an ideal light source. The unit of measurement for colour temperature is Kelvin(K). The measurement of daylight colour temperature is around 5,800 K. The Ideal Colour Temperature for surgical lights to be within the 3,000 – 6,700 K range, which is comparable with a daylight white colour of approximately 5,800 K only.
Maintaining optimal colour temperature is critically important, as it influences the colour and rendition of body tissue and fluids. Colour Rendition (85 – 100) is the measure of quality of light and it is often referred to as the Colour Rendering Index (CRI). Natural colours of objects are best visualized under the bright daylight, to which lighting devices are compared (reference value of 100). Lights with “good” colour rendition have a CRI over 80. Lights with very good colour rendition have a CRI over 90. Often regular lighting can distort the colour and appearance of objects, something that must be avoided during a surgical procedure. Therefore, the recommended Colour Rendition Index (Ra) for surgical lights needs to be between 85 and 100.
One of most important parameters that need to be considered in a surgical light is its ability to manage the shadow. Lights produce shadows when interfered with, surgeons need shadow managed light for clear visibility of surgical site deep cavities and its contours. Therefore, it is important to mange the shadow without compromising on the quality of deep cavity lighting capability. Cast shadows can be managed by multiple light sources strategically positioned, which also need to increase the contour shadows which helps surgeon’s visibility of deep surgical cavities clearly.
The best surgical light will have the highest volume of light at the cavity, even when the light is positioned more than one meter away from the surgical site. L2 measurement is particularly critical for deep cavity applications.
The uniform light volume is of great importance to surgeons which is achieved with the help of merging several light patches, shining at the same time and strength at different heights. This becomes necessary since the contours inside the cavity needs variable light dimensions. Volume of light is measured by an IEC standard equation: L1 + L2.
Light inevitably produce heat. However, the heat must be managed to avoid tissue desiccation or drying up of tissues which could cause sever consequences in sensitive surgeries and heat need to be managed for surgeon’s comfort, particularly when they operate on long-drawn surgical operations.
The heat radiance is measured at the light patch and at light-head. Although LED does not produced IR, it still produces some amount of heat. Since high luminance light produces more radiant energy, the IEC standard restrict a maximum of 1000W/m2 at the light patch.
There is no scope for error in a OR. It is of paramount importance that all the equipment and staff perform to the best of their ability in a fail-safe atmosphere. The surgical light need to be redundant in that in the event of a defect in any components, the light must be still operable with a minimum luminance of 40000 lx. The single dome light generally does not give fail-safe protection. A double dome luminary with separate transformers, fuses, wirings, and parallelly connected lamps or auxiliary lamps are likely to offer a fail-safe performance.
Vendor selection is hugely important in that proper products and services need to be acquired, preferably after verifying the evidenced existing performance of the vendor. Surgical lights which are Life Saving medical devices, which are made up of electronic and electrical components among other components are prone to break-downs, need to provide maximum uptime; say 95% uptime, which necessitates that proper Warranty, AMC, CMC arrangements are in place and the vendor must be selected considering the long term serviceability of the product based on the above and Life-Cycle Cost(LCC) calculation and existing evidenced performance.
