European patients undergoing surgery have about 2.6% chance to develop a post-operative infection. Besides pain and discomfort, these infections can lead to hospital readmission, additional surgical procedures and even the decease of the patient. The ventilation system provides clean air that descends on the patient and protects the patient from being infected by pathogens. The surgical lighting system provides adequate lighting to the wound, ensuring a high illuminance, even in challenging conditions as deep and narrow wounds. Currently, the protecting airflow is perturbed by the shape, position and heat of t he surgical lighting system, causing turbulent air flows. Post-operative infections may originate as particles from outside the protective zone enter the surgical site by these turbulent air flows. To reduce this disturbance of the laminar airflow by the surgical lighting, we have developed an integrated concept of an LED-based and automated light source, mounted above a transparent ventilation chamber. This paper outlines the optical design of the new surgical light source and its performance.

To obtain realistic results in lighting simulation software, realistic models of light sources are needed. A near-field model of a light source is accurate, and can be obtained by a near-field goniophotometer. This type of goniophotometer is conventionally equipped with a V(λ)-filter. However, the advent of new light sources with spatial- or angular color variations necessitates the inclusion of spectral information about the source. We demonstrate a method to include spectral information of a light source in ray tracing. We measured the relative angular variation of the spectrum of an OLED using a spectroradiometer mounted on a near-field goniophotometer. Principal component analysis (PCA) is exploited to reduce the amount of data that needs to be stored. Also a photometric ray file of the OLED was obtained. To construct a set of monochromatic ray files, the luminous flux in the original ray file is redistributed over a set of wavelengths and stored in separate ray files. The redistribution depends on the angle of emission and the spectral irradiance measured in that direction. These ray files are then inserted in ray tracing software TracePro. Using the OLED as a test source, the absolute spectral irradiance is calculated at an arbitrary position. The result is validated using a spectroradiometer to obtain the absolute spectral irradiance at that particular point. A good agreement between the simulated and measured absolute spectral irradiance is found. Furthermore, a set of tristimulus ray files is constructed and used in ray tracing software to generate a u'v'-color coordinate distribution on a surface. These values are in agreement with the color coordinate distribution found using the spectral ray files. Whenever spectral or color information is desired at a task area, the proposed method allows for a fast and efficient way to improve the accuracy of simulations using ray tracing.

Luminaires are conventionally modeled using a far-field representation. To calculate this representation, a photometer revolves a light source at fixed distance and illuminances are measured in a set of angular directions. Using the inversesquare- law, the far-field intensity, also termed luminous intensity distribution is then calculated. For Lambertian sources, the far-field starts from a distance of five times the maximal dimension of a light source; which is called the limiting photometric distance. The advent of luminaires composed of LED arrays with narrow beams have shown that this limit is no longer valid and far larger distances (up to 15 times the maximal diameter) are suggested by the lighting community. This problem is even more outspoken when the individual LEDs are focused at close distance, as in e.g. surgical luminaires. To overcome these problems, we exploit the use of a near-field representation to describe an array of two narrow-beam LEDs focused at close distance. For such a test source, this paper shows how a near-field luminance goniometer is able to construct ray-data. Ray files can be used to calculate a near-field representation and far-field representation of a light source. These measurements are validated by a theoretical derivation of the intensity of an array, using a simple analytical model to describe the emission of the individual LEDs. This near-field approach makes discussions to determine the far-field photometric distance superfluous.

Surgical luminaires are an important tool for the surgeon, yet highlighting the wound of a patient is not trivial and surgical luminaires must meet stringent regulatory requirements. Optical requirements and performance indicators are described in the European Standard for surgical luminaires and they must be measured after construction. Surgeons and hospital managers often use these performance indicators to compare different surgical luminaires. The introduction of solid-state lighting and high-power light emitting diodes (LEDs) has initiated a new generation of surgical luminaires. When designing a virtual prototype of a surgical luminaire it would be beneficial to have a cost-and time-effective method to test luminaires for compliance with the European Standard. Unfortunately, far-field intensities do not allow an evaluation of these luminaires with respect to the standard and near-field ray-data must be used. To validate this near-field approach, we used angular-and spatially-resolved ray-data of a luminaire and modeled a virtual setup that corresponds to the setup used in the European Standard. This paper compares illuminances obtained from simulations and photometric measurements of various photometric tests. Good agreement was found: relative differences between simulations and measurements for the central illuminances deviate maximally 0.4 percent (+ 3.2 percent, -0.4 percent), while the maximum difference for the various scenarios amounts to 5.6 percent (+/- 2.2 percent). The technique can be applied to virtual prototypes of surgical luminaires that are composed of optical components such as reflectors and lenses and use spatially-and angular-resolved luminance-data of individual LEDs. This permits us to check compliance with the European Standard before assembly. This method will allow for more economical and time-effective development of new luminaires that maintain the quality requirements.