MIT2_00AJs09_lab02

MIT2_00AJs09_lab02 - MIT OpenCourseWare http:/ocw.mit.edu...

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MIT OpenCourseWare http://ocw.mit.edu 2.00AJ / 16.00AJ Exploring Sea, Space, & Earth: Fundamentals of Engineering Design Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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1 LED Light Bank Assembly Jaime Mateus, Roedolph Opperman The goal of this module is to construct a relatively simple and inexpensive LED light bank for underwater illumination. 1.1 Background: An LED is a Light Emitting Diode. Like a normal diode, it consists of two pieces of semi-conducting mat e rial (one P-type with positively charged particles and one N-type with negatively charged particles) bonded together to form a P-N junction. Current flows easily from the positive P-side (the anode) to the negative N-side (the cathode), but flows very poorly in the opposite direction. Charge carriers (electrons and holes) flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, releasing energy in the form of a photon. If the change in energy level is large enough, the photon will have a wavelength in the visible spectrum and will emit visible light. LEDs have a number of advantages that make them ideal for underwater lighting. Water absorbs different frequencies (colors) of light at different rates, so some colors (especially blue and green) are more suitable for underwater illumination. Since LEDs generate color on a specific wave length, they do not generate the visible wavelengths that will merely be absorbed by the water so they are more efficient than multiple spectrum white light. They also do not use filaments to generate light, so they lose less energy to heat generation; they tend to dim over time instead of burning out abruptly; and they have a much longer life ( ~ 10 years) than incandescent bulbs. The LED packaging also makes them more resistant to vibration, damage, flooding and shock than other lights and focuses the light. LEDs do have some disadvantages. They tend to be more expensive than other lighting sources and their lifespan is related to operating temperature (overheating will cause premature failure). However, the ocean serves as a heat sink and should minimize the risk of premature failure and the increased cost is insignificant compared to the benefits. © Copyright MKThompson 2006 - revised 2009
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2 1.00 Wavelength, µ m Let the area under curve = 100% of surface solar energy Sea surface 0.70 0.60 0.50 0.40 0.30 1 1.1 1.6 2.5 5 5 4 6 7 6 1.2 Relative transparency to wavelengths (on a scale of 10) Only 45% remains of energy incident on the surface Only 16% remains of energy incident on the surface Only 1% remains of energy incident on the surface 100 m 10 m Depth 1m red orange yellow green blue violet Figure by MIT OpenCourseWare. Figure 1: Light Absorption in the Ocean (www-ocean.tamu.edu)
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This note was uploaded on 01/28/2012 for the course AERO 2.0 taught by Professor Alexandratechet during the Spring '09 term at MIT.

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MIT2_00AJs09_lab02 - MIT OpenCourseWare http:/ocw.mit.edu...

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