Shedding Some Light on LED Luminaire Design

You don’t need to go to engineering school to understand that electric lighting produces heat as a by-product. And if you’re designing luminaires today, that simple fact guides much of your work. Removing heat is always a priority. In an incandescent fixture, heat buildup must be controlled for safety’s sake. In a modern LED luminaire, safety remains an issue and heat buildup can reduce the LED’s light output, causing a color shift while reducing the component’s useful life.

The key to successful luminaire design is to confirm that the unit can transfer heat efficiently from the LED’s PN junction all the way to the ambient air. Of course heat is a fluid flow, and complex fluid dynamics equations are outside the comfort zone of many designers—even though they did go to engineering school. For decades the hands-on work of computational fluid dynamics (CFD) analysis has been left to experts in lab coats.

Tools developed for the design engineer, now automate esoteric number-crunching steps such as cavity modeling and help ordinary users—not just seasoned CFD experts—get reliable, repeatable CFD analysis results. One such feature is the crucial step known as gridding.

Automated Gridding vs. Origami

Gridding, also known as meshing, precedes every CFD analysis. The concept seems simple enough: the surface of the device is mapped into rectangular cells, each of which is analyzed discretely. Essentially the whole surface of the device is broken into tiny, manageable localities. The analysis tool then develops a composite result that incorporates all of the cells in to a contiguous whole.

But gridding is not like folding a piece of graph paper, Origami-like, into the shape of the luminaire being analyzed. Yes, that would yield uniform resolution throughout, but it wouldn’t be sufficient for the most critical areas of the device.  New tools automatically scale down the cells in these vicinities. As the illustration shows, cells clustered around the LED are much smaller than those on the periphery of the housing. This feature, known as adaptive meshing, provides higher resolution where it is most needed. 


Computational grid (mesh) shown on a central slice
through the luminaire depicted in the inset image. Smaller
grid cells near the LED provide higher resolution for CFD calculations.

Automated gridding is an invaluable tool for any CFD analysis project. Making judgments about localized cell sizes is sometimes a cut-and-try process even for experts, but new CFD tools automatically optimize their grids to the geometries of the specific device under analysis.  Want to learn more about gridding? Read “How to Choose an Effective Grid System for CFD Meshing,” a white paper that explains grid technology and applications in detail.


This Quick Technical Quide has been provided courtsey of Mentor Graphics (Mechanical)

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