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.
Hi Lars,
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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Hi Jack!
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.
You mean that, while at 60 degree the specular reflectance is higher,
the average specular reflectance over all angles of incidence should be
the expected value of 76%? I try to get what the values really mean... a
desperate attempt without really knowing what had been measured.
Thanks! CU Lars.
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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Hi,
thank you for the reply! The material is an aluminium surface finish
with coatings. I do not know about the roughness yet, as it was not
provided. I know that the total reflectance was determined using an
integrating sphere, and at an angle of 30 degree (whatever this really
means in detail - where is the angle in this measurement?), the specular
reflectance was measured according to ISO 7668.
As far as I understand, the routine is to point a light source at the
sample point under the indicated angle (which is given as the angle
between surface normal and the line between the sample point and the
light source. On the opposite side, the sensor is pointed at the same
sample point. 60 degrees is a standard for aluminium measurements
according to the ISO 7668.
As the surface roughness influences the measurements, the term used here
is gloss (a nice explanation is found at wikipedia
http://en.wikipedia.org/wiki/Gloss_(material_appearance) ). If someone
can share a nice definition of the difference between gloss and specular
reflectance it would be highly appreciated 
And I have to read a bit before I can follow you about how to determine
the roughness.
CU Lars.
