Editing Passive solar building design (section)

====Angle of incident radiation====

The amount of solar gain transmitted through glass is also affected by the angle of the incident [[solar radiation]]. [[Sunlight]] striking a single sheet of glass within 45 degrees of [[perpendicular]] is mostly transmitted (less than 10% is [[Reflection (physics)|reflected]]), whereas for sunlight striking at 70 degrees from perpendicular over 20% of light is reflected, and above 70 degrees this percentage reflected rises sharply.<ref>{{cite web|url=http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd039_e.html|archive-url=https://web.archive.org/web/20090321191136/http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd039_e.html|archive-date=2009-03-21 |title=Solar Heat Gain Through Glass |publisher=Irc.nrc-cnrc.gc.ca |date=2010-03-08 |access-date=2010-03-16}}</ref>

All of these factors can be modeled more precisely with a photographic [[light meter]] and a heliodon or [[optical bench]], which can quantify the ratio of [[reflectivity]] to [[Transmittance|transmissivity]], based on [[angle of incidence (optics)|angle of incidence]].

Alternatively, passive solar computer software can determine the impact of [[sun path]], and cooling-and-heating [[degree day]]s on [[energy]] performance.