Overview

The aim of this app is to dynamically model the relationship between the spatial distribution of daylight and a room's size, aperture layout, shading devices and external obstructions. To make this process interesting and fun to play with, the calculations are optimised to be as fast and interactive as possible without compromising on accuracy. This means than you can change the room, its apertures or shading devices and the daylighting will update in close to real time, even on a tablet or phone.

To change the size of the room, simply select any of its bounding surfaces and then drag the appropriate arrow in the direction you want. To adjust an aperture or external obstruction, again simply select it by clicking or tapping on any of its surfaces and then drag one of the manipulator arrows that should then appear. The circular manipulator in the center of the object allows you to change its position. Whilst apertures are prevented from overlapping, you can still drag them into any area where they will fit, even within adjacent walls.

You can click or tap on any numeric value displayed within a dimension line to display a simple editor that lets you directly enter numeric data. Clicking or tapping in the INFO panel on the left will also display an editor for numerically adjusting the main parameters of the currently selected object.

Daylight Calculation Method

Daylight calculations use the split-flux method to determine the internally reflected component and raytracing to determine the direct sky and externally reflected components. Rays are used to calculate exactly which parts of the sky are visible from each grid point and which are occluded by external shading and obstructions.

Daylight illuminances are then calculated using detailed sky luminance distributions generated using the CIE Standard General Sky method described in both ISO 15469:2004(E) and CIE S 011/E:2003. You can selected any of the 16 standard sky types or load in a weather data file and have the sky distribution generated dynamically using hourly direct and diffuse solar radiation.

This approach has undergone extensive validation using direct comparison with the results of Radiance and DIVA/DAYSIM using the exact same room models, and the correlations are very close for most common room configurations. For anyone interested, a detailed report on the methodologies and results of this testing is available.

To test this yourself, you can export Radiance and DIVA/DAYSIM model definition files for the current room in order to render it yourself and directly compare results. If you don't have Radiance installed, there is even a remote render service that will allow you to do your own visual comparison.

Points of Interest

At the moment all the daylight calculations are being done in Javascript, which is still blazingly fast. However, I do have a GPU-based version which is even faster. But, given that there is so much else going on when you interact with the model (especially when contours are displayed and multiple apertures are being checked for overlaps), it turns out that the daylighting calculations are only a relatively small component compared to the geometry validation, tesselation, contouring and mesh regeneration process. Thus the speed increase due to using the GPU ends up not actually being that noticeable.

© Dr. Andrew J. Marsh, 2021.