Daylighting Innovations recently completed a two year research project developing and validating computer simulation methods for complex optical skylight systems. The work was done in collaboration with Architectural Energy Corporation, California Lighting Technology Center (CLTC), New Buildings Institute (NBI), Velux, LTI Optics (Photopia), and Lambda Research Corporation (TracePro). The report is in final processing, a draft can be sent upon e-mail request here.
This report details all tasks, findings, and recommendations undertaken for the Enhanced Skylight Modeling and Validation project. The scope involved developing and validating computer simulation alternatives to physical measurements for producing optical daylighting system photometry. The project plan included comparing several physical photometric measurements of optical daylighting systems to computer models, and validating the use of computer simulation to produce this photometric information. The key activities were skylight device measurements and material testing, data processing, and computer simulations setup and analysis.
To achieve a robust validation of the computer simulation methods, it was ideal to have physical skylight system measurements from a wide variable range of sky conditions as well as skylight systems. The selected skylight devices were tested at a goniophotometer testing facility located in Greenwood, South Carolina.
One key step in creating accurate computer models of the skylight systems was to model accurate optical properties of the surfaces in those systems. Visible reflectance and transmittance measurements were made for any surface that interacts with the optics of the system. Samples of these materials were cut from the actual skylights tested for detailed measurements of the transmittance and reflectance.
The simulation process used the created sky sources, the geometric models, and material models to calculate an output photometric distribution for comparison with the measured photometric distributions. Three software platforms were used: Radiance, TracePro, and Photopia.
Findings indicate that is possible to use computer simulations to accurately model and produce optical daylighting system photometry information. Further work is recommended to establish protocols for material testing and work with manufacturers to produce optical daylighting system photometry data for their products.