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Luminaire Design: Constructing a Reflector

October 5, 2010

fischerlighting

I was reminded this morning during class that, in the rush of everything going on in the studio last week, I forgot to write about the reflectors we designed and tested in Luminaire Design last Tuesday!  I just had to share this project because it was such a great learning experience, and a unique one at that.  I promise I won’t get too technical … I just wanted to share our results because it was such a fascinating insight into something that you run across almost every day, probably without even realizing it.  Have recessed lights in the ceiling of your house/office/apartment?  Each one has a reflector specifically designed to direct the light into your room!

I’ll start off with a picture of something shiny to keep your attention – my group’s finished reflector.  We spent a total of one class (that’s three hours) two weeks ago learning how these reflectors work in downlights (recessed lights) from the VP of Engineering at Edison Price, a man who is not afraid of formulas, calculations, and spreadsheets.  He started off class at 9AM by explaining how to mathematically derive the profile curve of a reflector using said formulas, calculations, and spreadsheets – most of which flew over our heads at such an early hour of the morning – and before we knew it the class was over and we were assigned to design our first downlight reflectors on our own!  Luckily, he left his lecture notes behind for us to follow as we all individually designed our curves to distribute light evenly on the floor.

Fast forward a week, and we all have our reflectors analyzed by our professor, Scott, learning where we can improve, etc.  Next, we are all divided into groups to choose one person’s reflector to design and test for the next class.  Our group chose a design based on a lamp type and reflector design that was drastically different from the other groups.  Needless to say, it wasn’t mine … I chose the good old fashioned A lamp (the common “light bulb”). Oh well!

Our group reflector design was now based around a 20W G4 Bi-Pin Halogen (a bright little lamp about the size of your thumbnail) with an aperture opening of 4 inches.  Thanks to our trusty friends AutoCAD, CNC laser cutters (so cool), and adhesive mylar (the shiny, reflective material), our group printed and assembled our design in less than three hours, and you saw the results of our labor in the photo above.  How did it perform, you ask? Well, that was the most interesting part of the whole project: testing our prototypes.

For the testing we temporarily turned the Parsons light lab into our light metering facility.  You can see the basic setup here, where we positioned a light meter approximately five feet away from the reflector (we would compensate for the short distance with simple math), and measured the luminous flux (lumen output) of the reflector every 10 degrees radiating out from the center line of the reflector (imagine that the long metal beam holding our light meter rotates on a hinge positioned directly above the reflector).  We entered each value into a chart and then rotated the reflector onto a different axis to do the same thing, ending up with three axes of data for our designs (0, 45, and 90 degrees).  Scott then entered the data into an analysis program to generate charts like these for each group.

In short, this luminance distribution curve (values along the top are in lumens) tells us is that we have designed a narrow beam spotlight (most of the light is generated between zero and 20° off-axis), and that we still have some work to do to create a symmetrical reflector.  If our reflector had truly been symmetrical, the three separate curves would all be lined up, however, most of this was probably due to our manufacturing and assembly processes, which were less than … precise.  At any rate, it’s incredible to have this kind of factual data to support our design, as this is the same kind of data available for any other kind of reflector or lamp out there.  For those who are not as fond of reading charts (like me), here are some photos of the final results.

In the end our design was quite successful, despite some heat management issues (hot lamp + cardboard = sad Smokey the Bear).  Scott pointed out that to improve our design, we could have cut off some of the direct light from the lamp (seen above as the dimmer “halo”  around the bright, center beam) by placing a smaller aperture opening in front of the reflector (a donut, in theatrical terms).  We, then, would have had a very bright, narrow beam spotlight!

Overall it was a fantastic experience, if not a bit of trial-by-fire, learning how the optics of a reflector work and having a chance to design and test our own, as that information informs the basis of almost every type of commercially-available fixture out there! Heck, it even applies to theatrical fixtures!  How cool is that?  That’s right: pretty cool.

Hopefully I didn’t lose anybody along the way in my most technical of posts so far; but if you nodded off I won’t be offended … I’ll just shine a bright light in your eyes!  You know I can do it!

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