different surface reflectance, but same lighting result

[Anonymous]

Hi all,

I am quite new to Ecotect, but I;m trying to study how the reflectance factor on the surface outside the room would affect the lighting level in the room, but I dont think they quite show the correct result.

I've done a very basic room with a external surface to test this (picture), but both scenario has the same average lighting result of 115.94 lux.

Ive used ecotect material both poolwater, and exposed ground for this. Thay have significant difference in reflectance factor. 

Wonder if someone can hep me on this. thanks.

[Pennetier1]

Hi eujinlim.is, sorry for the late reply... I am going through old unanswered posts...

I suspect you  are using the internal Daylight Factor engine of Ecotect to perform this analysis.

There are some limitations using this method, as the Externally Reflected component (your ground surface) is probably not reaching your analysis grid.

The method sprays "rays" from your grid toward the window and if it "sees" an external object (on a different zone), then that will contribute to your Externally Reflected component.  However, once the ray passes through the window, there are no inter-reflection.  This means that if your grid points cannot see the external object, it will not contribute to the overall daylighting.  If your grid was set toward the ceiling, it would probably be able to see that ground plane.  If you have a vertical object obstructing the window and seen by the grid, such as another building in front of your window, then it would be very obvious that the obstruction's reflectivity contributes to your daylighting.

Usin the Radiance engine with Ecotect can help with this, as the inter-reflections will be accounted for, i.e., your grid points might see your ground plane through inter-reflection with the ceiling plane.

Also, note that by default, the "ground plane" in Ecotect (where the grid is laid), has an automatic ground reflection of 0.20 - this cannot be changed, so if you want to simulate water or snow, you would have to do what you were doing, creating a new plane with the appropriate reflectivity.

I hope that helps.

Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.

Cheers,