28 Team LED ME 4054, Spring 2008 7. DESIGN OVERVIEW Fig. 5 shows a solid model of our final design, and Fig. 6 shows a picture of our final prototype. FIG. 5. SOLID MODEL OF LUMINAIRE FIG. 6. FINAL LUMINAIRE PROTOTYPE Our design is relatively simple. A total of 30 LEDs are used in the luminaire²achieving predicted luminaire output of 1315 lumens. They are divided equally among two heat sinks and spaced 2.8 inches apart. All the LEDs face upward towards a diffuse reflective surface29 Team LED ME 4054, Spring 2008 in the shape of a double parabola. Each row of LEDs is strategically located at the foci of the parabolas²resulting in even light distribution from the luminaire. An example of this is shown in Fig. 7: FIG. 7. EXPECTED LIGHT DISTRIBUTION The heat sinks themselves were designed to maximize the natural convection heat transfer coefficient across their fins. Their slotted design allows for buoyancy driven channel flow across the fin surfaces and also minimizes the blockage of light reflected from the parabola. Fig. 8 illustrates the natural convection streamlines across the heat sink fin surfaces: FIG. 8. NATURAL CONVECTION STREAMLINES ACROSS HEAT SINK FIN The heat VLQNV HDFK FRPSULVH IRXU ILQV ZKLFK DUH ´ LQ GHSWK DQG ´ LQ WKLFNQHVV 7KH ILQV DUH VHSDUDWHG E\ WKUHH ´ WKLFN VSDFHUV DW HDFK RI WKH  /(' PRXQWLQJ ORFDWLRQV Fig. 9 shows a rendering of a heat sink cross section and an LED junction.30 Team LED ME 4054, Spring 2008 FIG. 9. HEAT SINK CROSS SECTION AND LED JUNCTION $OO FRPSRQHQWV RI WKH OXPLQDLUH ILW LQVLGH D ¶ ; ¶ HQYHORSH31 Team LED ME 4054, Spring 2008 8. CONCEPT GENERATION AND SELECTION 3M allowed the team freedom to design any lighting component we desired. This freedom made the scope of the project very open ended. It also meant that a large amount of time had to be put into the concept generation and selection process, to ensure the team selected the best possible concept for our final design. To narrow down the scope of this project, the team went through three separate concept generation and selection phases. The team started with general light applications, then focused on a specific fixture category, and finally chose a final fixture design. The following sections will discuss separately the processes used in each concept generation and selection phase. 8.1 GENERAL LIGHTING APPLICATION The team decided to research all general lighting applications that would be feasible candidates for LED technology. Some examples of the lighting applications considered include overhead spot lighting, outdoor lighting and desk lamps. Fig. 10 lustrates examples of these lighting applications. (A) SPOT LIGHTING (B) OUTDOOR LIGHTING (C) DESK LAMP FIG. 10. LIGHTING APPLICATIONS32 Team LED ME 4054, Spring 2008 8.1.1 Concept Generation The team discussed possible lighting applications that would benefit from LED technology, and also have a large market. Each team member was assigned specific lighting applications to research and was instructed to find out all areas where the lighting application is used, what products are already on the market using LED technology, and what patents exist for these products. Team members used the internet, patent searches, and consultation with 3M sponsors to gather information. 8.1.2 Concept Selection Once a sizeable amount of information was found, the team discussed the pros and cons of each lighting application. Each team member shared what they had found with the rest of the group and made a recommendation of how feasible each application would be to build. After D WKRURXJK GLVFXVVLRQ WKH WHDP GHFLGHG WR GHVLJQ D ¶;¶ OLJKW IL[WXUH IRU FRPPHUFLDO applicaWLRQV 7KH WHDP GHFLGHG RQ WKLV W\SH RI IL[WXUH EHFDXVH WKHUH DUH QR ¶;¶ commercial light fixtures on the market, utilizing LED technology, and because commercial lighting offers a large potential market. 8.2 SPECIFIC FIXTURE CATEGORY Once the team decided upon a commercial light fixture, the next step was to determine a specific fixture category. The team determined that the different fixture options included direct lighting, indirect lighting, side lighting, recessed fixtures, and hanging fixtures. Examples of the first three fixture options are illustrated in Fig. 4. Recessed and hanging are illustrated in Fig. 11. The following sections will talk about each category along with the pros and cons of these fixtures ending with an explanation of how the team chose the recessed fixture with indirect lighting.33 Team LED ME 4054, Spring 2008 (a) Recessed Lighting (b) Hanging Light Fixture FIG. 11. SPECIFIC FIXTURE OPTIONS CONSIDERED 8.2.1 Concept generation The team first researched different fixtures available on the market. A web search was done by each member of the group on a specific commercial lighting manufacturer. The team found that commercial fixture designs were either recessed into the ceiling or hanging down into the room. Upon talking to an expert in purchasing commercial light fixtures, the team was told that recessed fixtures were more commonly used than hanging fixtures in most commercial buildings. This information, paired with a large market, helped the team to decide on a recessed fixture for our project. The next step was to have each team member come up with at least ten design concepts to share with the group in the next meeting. After all the concepts were shared with the team, a group brainstorming session took place to determine strengths and weaknesses of the designs. Team members were instructed to come up with additional design concepts to be reviewed in the next meeting. At the next meeting the team shared their concepts and participated in a final brainstorm session to ensure all ideas had been exhausted. 8.2.2 Concept Alternatives After brainstorming sessions and research, the team came up with several concepts. We were able to group these concepts into three categories based on the way each design distributed light. These categories were direct lighting, side lighting and indirect lighting. Each category is discussed in