[Radiance-general] Re: diffuse + specular > total reflectance?

[yijun huang]

Hi Lars,Just wondering, do you have a roughness value (RMS) or equivalent from the manufacturer?If not, could it be possible that the 60-degree measurement is used to define the roughness value? The higher value (82) seems like a way to define the BRDF.i.e. BRDF(theta-i, phi-i, theta-r, phi-r) = 82/76 = 1.079You'd need to know (manufacturer definition)what the actual angle configurations (theta and phi) are for the 60-degree measurement, then working backwards using the Radiance equation, you'd get the roughness (RMS) value.for example, if both angles are zero, roughness = 0.272.if both angles are 30 (60-degree split evenly), roughness = 0.292 What exactly is the material? If it is more smooth than rough (polished metal rather than plastic-ky) then obviously my guess is wrong. cheers,YC Huang  I think that what you want to do is:

    <total reflectance> - <diffuse reflectance> = <specular reflectance>

    thus

    86 - 10 = 76

The specular reflectance that is provided is for a measurement at 60 
degrees incidence, if I understand this correctly.

-Jack

Lars O. Grobe wrote:
> Hi,
>
> as this may be because of some standards that I am not aware of, I 
> have a question about a record of material properties that I do not 
> understand yet.
>
> I have a high reflective surface, and the manufacturer gives me these:
>
> reflectance specular   60 degree: 82
> reflectance diffuse:                        10
> reflectance total (ASTM E1651):   86
>
> If I add 82 and 10 I get 92 > 86 for the total reflectance. So what 
> does this mean, are the values related to the way the reflectance is 
> measured and calculated using different procedures according to 
> standards?
>
> CU Lars.

 

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