1. High power LEDs for such an application were not commercially abundant in year 2002-2003. As a result, the team chose Luxeon Star LEDs with a rather limited number of options in terms of power and specifications.

2. There are some power interface challenges between what’s available in the airport and the LED devices. Between MALSR (Medium Intensity Approaching Lighting System) and ALSF-2 (High Intensity Approaching System), there are different standards involved. For example, MALSR is a voltage-based system, and the existing MALSR system steps down from 120VAC to 50VAC for the incandescent bulbs. While ALSF-2 system is a current driving system, and it uses power regular to support 5 different AC current levels for the different operational needs. LED devices are DC current driven, so the circuit interface between existing power structure for the two systems and the LED light bar prototypes must be resolved. All the design alternatives must meet the FAA regulation, and some modifications are not possible with the existing airport power and cabling standards. A simple bridge rectifier and filter system was chosen to convert the AC voltage to DC voltage. Resistor networks were incorporated carefully to control the required luminance based on the theoretical analysis and estimates. For the ALSF-2 system, the incoming current level was much higher than what’s required and handled by LEDs (~30 times more), therefore, current transformers were incorporated to step down the current to each string of LEDs. Rectifier and filter circuit was similarly incorporated to convert from the initial AC circuit to DC circuit.

3. The design of the light bar must incorporate reliability consideration. The team decided on 5 parallel groups, each with 16 LEDs in series to make up the sufficient luminance and power. The choice of the current regulating resistor must be able to handle large amount of the power because these LEDs are running at high power level for sufficient luminance. The light bar built from aluminum served well as the structural support and provided the heat sink needs.

4. Testing was completed both in the lab as well as the field. In the lab, we can test the power consumption of the whole bar and reliability of the overall system. Field testing is extremely important because LED light color is different from incandescent lighting. Even though luminance is one way of measurement, it is ultimately to the eyes of the pilots who uses the flight approaching system during the landing process. The optics of LED is not optimally designed for such an application; therefore, a luminance estimate for short distance is quite different from above sky. This can only be examined and validated through the field testing. Direct feedback from the pilot in the field is very important. The light approaching system is mostly useful at night landing, so the field testing must be carried out at night. There is a large effort to set up the field testing with a local airport because of the complexity of air trafficking. We were lucky to have a volunteer pilot from the college who conducted the flight with the students and provided feedback. The ground crew has to communicate with the sky for different testing purpose. It takes effort and iteration in the process. For example, Figure 1 shows the successful lab testing and the failure of the initial field testing because of the interface issues of airport power system and prototypes. The final field testing performance was shown in the Figure 2 as the light bar is visualized in the sky. Considering the complexity in logistics and safety needs, this was an extremely rare kind of testing that happened in Clinic program.

5. Additional considerations include thermal consideration and cost analysis. The fact that incandescent lights melt ice and snow naturally because of inherent heat. LED lightings are much more power efficient which is the main drive of the project, but it doesn’t handle ice and snow on its own. Therefore, an additional heating system and control/sensing system should be considered if such system is deployed at locations weather encounters ice and snow regularly. In additional to the prototype cost, some estimate of the overall system cost was also included.

1. At the time, the Luxeon LED were fairly early generations of the devices, and the focusing optics was not quite ready at the time of the prototyping. Therefore, the angle of light distribution is rather large. In the far distance of space, the amount of lights that approaches the aircraft is rather small portion of the overall light intensity from the devices. Therefore, it appears dim and thin strip of lights in comparison to the existing system. More light bulbs and power might be needed to increase the brightness of the light bar and width of the light bar.

2. The following year, a different Clinic team tested new LEDs with better focusing optics. Extra focusing is not good either, because it also has to support the flight range (both height and distance of travel) where the approaching lights need to be visibly brighter. In principle, a more specialized focusing lens that supports or optimizes for such range could be incorporated, but it is not readily from manufactures and easily tested. In addition to the static performance, the follow up team also introduced and explored a potential flashing mode that can easily adjust the flashing pattern for the pilots, and increase the visibility needs of the approaching system. It provided a very promising solution.

1. Design various alternatives that fit to the specified space. The team explored 4 different designs all with the uniformity requirement in mind. The light bulbs must be incorporated mechanically and electrically, and uniformity must be achieved through the clever design. The following three examples illustrate completely different approaches to provide uniformity. In the first design shown in Figure 3(a), everything is static, and the ring of lights in the bottom of the dome in combination of the full reflection coating and dome shape provide the uniformity of lighting in 3-D space. The second design idea is to use 2-D uniform light sources such as fiber optic panels to assisting forming 3-D uniformly lighted space. The design alternative in Figure 4 requires fast rotation of the arc where a set of bulbs are located evenly to provide 3-D uniformity. This design requires mechanical design and machining skills as well as proper electrical set up for the lights and motors. The exact same design is used as the uniformity detection apparatus if the light bulbs are replaced by photodiodes in the strategic positions for volume uniformity (angle, height) measurement.

2 Specify the uniformity metric. Measuring uniformity in 3-D space is not an easy task. Even though there are many existing metrics for different purposes, the team still have to decide on which measure is appropriate and good fit for the application. Statistical quantities Kurtosis (measure distribution tails in a set of data) and coefficient of variance (CV) have been chosen as the 2-D uniformity. A specification of 7% CV and -1 of Kurtosis is given by the UVP as a benchmark. Both angular and planar illumination data are evaluated using the statistical analysis to form an understanding of 3-D uniformity. The team has to develop Matlab scrips to automate the reading of the data and statistical analysis of the data. The hemisphere testing devices as in Figure 4 provides two angular degree of freedom, and positions provide increments of 16 degree increment.

3 Making the prototypes involve a lot of hands-on work. Each design includes some mechanical construction, circuits for light bulbs. For example for the fiber optics panel prototypes, due to the high cost of commercial product, the team create a winding system inhouse, and tried sandblasting to create uniform removal of the cladding layer for lights to uniformly emit from the panel. Chemical etching was also experimented to examine the easier control of the process.

4 Both the experimental testing and simulation were completed to validate the uniformity specifications. For the experimental data, the same arc design shown in Figure 3 was used for a set of photodiodes to collect brightness information in the given coordiate system and 2-D planes. A map of two angular dependance over the whole volume can also be generated. Data acquisition and synchronization with the motor driven system is set up as well as the post-procession of data. In comparison to current light system (current product line) performance of 8.2% CV and -0.3 of kurtosis, the rotating arc design performed well with 2.82% CV and kurtosis of -0.8. In addition, Tracepro analyzed and validated the feasibility of the dome design concept. Angular mapping illustrate the spatial symmetry or assymetry, so it provides additional insights of the 3-D spatial uniformity performance.

5 As a part of the business development, the team also pursued SBIR grant submission. This was an excellent opportunity for the team to fomulate the project aims, describe the usefulness of the innovation, provide preliminary data and research findings of the Clinic project, as well as the overall plan of the proposal.

1. The size of the tools is small. Even though we are introducing a completely new technology into the existing surgery, because of the standard ways of conducting these surgeries, the size of the tools that the design must fit in limit the solutions to a rather limited small number of choices. In addition, for safety and manufacturing cost consideration, the designs must be simple and reliable. Figure 5 illustrates typical surgical setting and tool sizes. The trocar sizes are typically range from 5mm-12mm in diameter, maybe rarely to 15mm to maintain the small incisions for such a surgery. The light for illumination and the camera for images/videos to transmit to outside display monitors should be integrated as much as possible. Multiple light sources in different incision might be desired to create shadow and depth perception which is one of the shortcomings of the single light source setting of the current system. A central trocar that allows for the surgeons to conduct the observation with sufficient lighting is necessary for precision of surgical procedure. The team finds there is tradeoff between the size of the tool design and the space to accommodate brighter lights thus better performance. Adjustable light intensity is also desired for different operation conditions and for power reservation needs. Careful decisions should be made, and variation of the designs should be offered for the liaisons/doctors for their feedback.

2. The team focuses on the mechanical design of the lights that fit with exiting tools, and makes it more versatile. A direct feedback from the liaison who are doctors in this case are extremely valuable, so that teams can decides on the need for the surgical setting. Observation of the actual surgery was arranged to see the typical operation habits of the doctors during such surgeries. These user experiences are critical in the prototype design phase. Similarly, the team conducted several field tests to evaluate the lighting and camera system prototypes in an emulated surgical setting. A direct comparison with the existing system is possible. These are all critical steps in the successful outcome of the project.

3. There are some in house manufacturing limitation for the prototyping stage. While 3-D printing is readily and conveniently available for fast prototyping and idea validation, some of the more sophisticated designs require more precise control of the material such as plastics become a limiting factor. For example, a plastic tube with precise control of the inner diameter and outer diameter, or curvature required for different size needs (small for the lower end for trocar size requirement, but larger to accommodate circuits and battery at the bub area). Even though once we have the idea and design, injection-molding could be used to achieve these needs, it was not as accessible to the team and the manufacturing requires longer time and more initial cost, so we have to stay in the proof-of-concept stages. In a few cases, students have to stay with a slightly larger size for the ease of machining.

4. There are many choices for the camera. For the necessary resolution, higher performance cameras are desirable. It is not easy to integrate the camera chip and transmitter/receiver circuit, with the lighting tools for the given space. A more complete design and design iterations need to happen within the time frame. This sometimes pose a challenge with the multiple aspects of requirement (spatial needs, power/intensity requirement, manufacturability, system integration).

5. In this particular case, the team is more hands-on mechanically than electrically, so the final prototypes and deliverables achieves more success in the mechanical design aspects than the electrical implementations. Students background could potentially shift the direction of the development when multiple goals compete with the students’ time and contribution. Feedback from the liaisons also influence the direction of the development.