[Radiance-general] irradiance vs. radiance / luminance vs. illuminance

[Lars O. Grobe]

>
> Perhaps 0.25 is a bit too high for asphalt but reasonable for concrete? 
> BRE [1] list a table of surface reflectances with asphalt = 0.07 and concrete = 0.2 ~ 0.3.  Anyone know of a more detailed reference for surface reflectances?
>   
I think in this case, taking a grey chart, going out and finding the
value by comparision would work well. The problem is that there are so
many different types of concrete (granularity, additions, surface
finishing) plus outside factors (wet / dry etc) that you cannot get one
color / reflectance for the material.

BTW if I look at the road in front of the office I am working in right
now, I also wonder if the reflectance of the real-world asfalt is not
much higher. The 0.07 may be "pure" asfalt (so almost black as bitumen)
while the road surface here contains sand and stones to make it rough
and dureable. So if you walk around with your grey chart, just make one
more comparision ;-)

One problem with outdoors surfaces is that the values measured in lab
can be far apart from real world. Erosion, dust, humidity, vegetation...
many factors affect what we see outside, besides the pure "material". So
I guess in a proper simulation, one should always try to check these
reflectances, at least if they have big influence on the result.

CU Lars.