Daylight Analysis

This is a re-working of my old Real-Time Dynamic Daylighting applet. It originally began as an experiment in real-time ray-tracing, trying out some daylight-based optimisations I had been thinking about for a while. However it quickly became apparent that ray-tracing wasn’t actually needed in convex shaped rooms without any internal obstructions, so the calculation could be made much faster by simply applying the algorithms as efficiently as possible.

Thus, for a simple rectangular room, this app lets you interactively manipulate its proportions, surface properties, the number, size and position of windows in each wall, as well as the glazing transmittance, and then see the working plane daylight factor distribution automatically update in real-time.

In addition to just the daylight calculations, there is enough spare CPU for displaying interactive information overlays. If you use the popover buttons in the bottom-left of the window, you can overlay the frequency distribution of daylight factors over the whole room or even a visualisation of the daylight factor protractor calculations for the currently selected window. Some of the overlays also include dynamic sliders that let you change room properties and see their effects update dynamically.

Calculation Method

This tool uses the split flux method developed by BRE, with all the required daylight factor protractors and nomograms converted into look-up tables. Whilst I have some working models that handle internal obstructions and rooms of any shape, they need more work before they are fast enough and robust enough for general use. Thus, the model used here is based on a rectangular room and, being so relatively simple, the calculated daylight levels match up pretty well with results for the same room models generated in Radiance.

Complain all you like about the accuracy of non-ray-traced daylight calculations, but they do have a very valid place in conceptual design - helping designers get much closer to their performance goals much earlier, before having to spend time and money validating in something like Radiance or 3DS Max Design.

The kinds of real-time dynamic calculation and visualisation available in tools like this not only help designers design, but help them develop a much deeper understanding of the complex relationship between geometry, materials and performance.

Understanding the potential distribution of daylight within a room given the size and position of windows is an extremely useful design skill. Yes it’s possible to use daylight analysis tools to simulate it, but no-one does this for all rooms whilst preparing and iterating over initial layouts. However, if you have this understanding already, it automatically feeds into all the decisions you make as you layout each room.

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Change Log

1.0.0 2014-05-12

• Initial release.