I have a question concerning the light source (.sky file) for daylight factor simulation.
While comparing the results with Dial+ and radiance/sketchup, I found out that honeybee isn’t considering ground glow (usually representing a 20% ground reflection) while other software do consider it.
This leads to lower results of daylight factor all over the zone, but particularly on the back on the zone as it is mainly lit by groung glow in other softwares.
So my questions are :
1 - Is this difference normal / wanted ?
2 - Is there a way to consider ground glow easily (I tried modifying the sky file before launching the simulation but it is overwritten each time)
3 - Is HB[+] doing the same thing or not ?
Thank you for this remark. I agree with you on this but am quite surprised as other software do consider a “luminous ground” anyway. It seems HB+ and other recipes include a luminous ground while the DF recipe in HB does not.
Although it might seem too self-evident to point out, we should remind ourselves
that at the horizon the sky “meets” the ground. An actual ground plane of finite
extent, say, a disc of radius r, will always fall short of an “infinite” horizon. For any
given view toward the horizon, we can make the gap (a black void) between the
edge of the ground and the sky appear smaller by using a larger r. However, we can
never make them meet. Furthermore, there are good reasons not to introduce an
actual ground plane of inordinately large size: the resolution of an ambient calculation
will be dependent on the maximum dimension of the scene.
To get around this problem, we use an upside-down sky to represent a luminous
ground. To do this, we apply the skyfunc modifier to a 180-degree glow source,
where the direction vector is pointing downward.
It seems indeed that without this luminous sky, daylight factor results are quite pessimistic, even with a local ground plane with 20% reflectance.
I will continue my research on the subject but would be very happy to have your insight on the subject.