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Tunable Spectrum Light Fixture

Written by Emmett Milliken
Intelligent Illumination Getting the right lighting is tricky, especially when you’re trying to shoot a video. Any given room may have multiple inside light sources combined with sunlight from a window. But what if you could replicate that ambient light by mimicking the spectral power of any light source? In this project article, learn how this Cornell student built a system to do just that, using a PIC32 MCU, LEDs and the DMX-512A smart lighting protocol. Topics Discussed How to build a system that replicates ambient light by mimicking the spectral power of any light sourceHow to implement the DMX-512A smart lighting protocolHow to control LEDs using a PIC32 MCUHow to craft a user interface using a three-digit, eight-segment displayHow to develop multi-threaded software using the stackless threader Protothreads Tech Used Microchip PIC32 MCUMaxim Integrated MAX481CPA+-ND RS-485 transceiverMean Well PS-255 5V power supplySaber Z4 LEDs from Luxeon Star LEDsBCD to seven segment decoderMathwork’s MATLAB Inspiration for this project came from the idea of a light fixture that could duplicate the ambient light in a room. The motivation for this was for situations such as making videos indoors, where there might be multiple light sources, including sunlight and overhead fluorescent lights, yet still not enough for recording. In working toward that concept, I developed a light fixture that can be tuned to mimic the spectral power distribution (SPD) of other light sources (Figure 1). The SPD of a light source determines both the overall perceived color of the light and how clearly the colors of an object are illuminated by that light. FIGURE 1 - My tunable spectrum light fixture LEDs serve well as a tunable light source, because they have a narrow enough spectral bandwidth to allow for fairly distinct regions of control. At the same time, their bandwidth is wide enough to cover the visible spectrum with a reasonable number of individual types
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Tunable Spectrum Light Fixture

by Emmett Milliken time to read: 11 min