Hi Christopher,

one rather simple way to estimate reflectance of mostly diffusely reflecting surfaces is to use a gray-chart. The ColorChecker by Gretag/MacBeth is rather popular for such applications. Often you do not need color, and I would not worry too much if you are off by few percents here.

Specular reflection is a game changer, it is rather hard to estimate and introduced the question about the exact characteristics of the specular component. Radiance uses a Gaussian representation for the specular reflection, with an additional roughness parameter to describe the "sharpness" of the reflection. Imagine the difference between a polished aluminum surface and one with some roughness, they will both mostly reflect to the specular direction but highlights will be spread by the roughness of the latter.

Glass obviously is crucial for your simulations, and before thinking about measurements I would have a close look at the International Glazing Database. I would not guess when it comes to glazing.

The case of translucent panels is probably one of the most difficult ones. For a meaningful analysis, you need to know not only the typically given direct/specular transmission/reflection, but the angular dependence of both (the scientific term would be the Bidirectional Scattering Distribution Function BSDF). There are very different "white translucent" materials, which may share the same direct/specular transmission and reflection (as found by direct-hemispherical measurements using e.g. an integrating sphere), but lead to very different effects and require different models. E.g. it makes a difference wether scatter is caused by surface roughness, or by inclusions in the volume of a transparent solid. The latter may have perfectly smooth surfaces and show sharp, mirror-like reflections, while the surface roughness would effect both reflection and transmission. Radiance provides the trans material class, but this comes with a lot of assumptions...

Besides it may also have the most significant impact, depending on the height of the partitions. On the one hand, the scattering properties affect how much light is transmitted to a direction where it is accounted for in work-desk illuminance. If the scattering effect is very strong, only a small fraction will pass through towards a desk behind such a partition, and quite a lot of light will be scattered towards directions where it is kind of lost for your "useful" illuminance on the work-desks behind (a perfect diffusor would equally scatter light to all directions, so to the ceiling, floor, ..). What may even be more crucial is the fact that the scattering properties may lead to glare, if the partition is hit by direct sun-light. Light that would otherwise reach a work-desk or floor may be scattered in a way that a significant portions goes straight towards the eyes of occupants - that is why materials with a strong scattering effect are rather difficult to handle if they may be exposed to direct sun-light.

For translucent panels I would thus recommend going with measured BSDF data. Recent versions of Radiance allow you to use the data-driven BSDF material class, which is directly based on measurements and does not rely on all the assumptions inherent in the trans model. There are laboratories offering such measurements dedicated to applications in daylight simulation (LBL in the US, Pab-opto in Germany, my employer Lucerne University of Applied Sciences and Arts in Switzerland), and databases are created to make more data accessible. You may contact the supplier of the product to provide you with data, and if not available, hint them at those labs. I think that it is important to rise awareness for the importance of realistic models. Too often a lot of effort is spend on running complex simulations and analysing results derived from models based on nothing but guessing.

Do not spend time on textures if you are looking for illuminance, they have virtually no impact and take your valuable time. And do not estimate from photographs. Cameras have a lot of image-processing built in, the pixel values have little to do with reflectance.

Cheers, Lars.

zgfDisclaimer

Here?s one good set of tables to start with ? you?ll find google is your
friend to look up specific material/product properties.

http://www.uncg.edu/iar/elight/learn/determine/lc_sub/mat_prop.html

As a general rule, I was taught for photometrics it?s safe/conservative
when actual finishes aren?t known to start with reflectances of 80-50-20
for ceiling, wall, and floor surfaces respectively. That?s representative
of typical white ceilings/tile, walls of light-to-medium colors, and dark
carpet/flooring.

Colored/textured surfaces can be tricky to estimate. Sometimes it?s
helpful to switch an image or swatch of the color/pattern to grayscale to
help estimate where on a scale of 0 to 1 the reflectance value should lie.

It?s also helpful to be aware of some real-world examples to set
boundaries:

- Fresh asphalt situates around 5% reflectance (0.05)

- Freshly fallen snow reflectance is around 90% (0.90)

- Most common building materials and finishes should situate
between those extremes

- White suspended ceiling tiles in particular can range from ~75
to 90% reflectance, with higher values typically costing a premium.
Reflectance is commonly stated on spec sheets and sometimes in
architectural specifications (that goes for most commercial paints as well).

I hope that helps!

~Nick

*NICK CATON, P.E.*
*Owner*

*Caton Energy Consulting*
306 N Ferrel

Olathe, KS 66061

office: 785.410.3317

www.catonenergy.com

*From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf
Of *Jones, Christopher
*Sent:* Thursday, September 17, 2015 2:50 PM
*To:* bldg-sim at lists.onebuilding.org
*Subject:* [Bldg-sim] Radiance Materials database

I am looking for some example materials I can use in a Radiance simulation
for daylighting calculations for LEED v4. The project is your typical open
office concept with half-height partitions between work stations.

The partitions are a white, translucent material. The workstations are a
wood grain laminate, the walls are flat off-white, the carpet tiles are a
blue-gray color. I can get the colors from photographs of the materials
but I am not sure how to estimate the reflectance. Also, I am not sure of
how to handle the texture of the carpet tiles.

Thanks for any assistance!

[image: cid:image003.png at 01D09C46.E75BA0D0]

*Christopher Jones,* P.Eng.
Senior Engineer

*WSP Canada Inc.*

2300 Yonge Street, Suite 2300

Toronto, ON M4P 1E4
T +1 416-644-4226

F +1 416-487-9766

C +1 416-697-0056

www.wspgroup.com

------------------------------

You are receiving this communication because you are listed as a current
WSP contact. Should you have any questions regarding WSP?s electronic
communications policy, please consult our Anti-Spam Commitment
www.wspgroup.com/casl. For any concern or if you believe you should not be
receiving this message, please forward this message to us at
caslcompliance at wspgroup.com so that we can promptly address your request.
This message is intended only for the use of the individual or entity to
which it is addressed, and may contain information which is privileged,
confidential, proprietary or exempt from disclosure under applicable law.
If you are not the intended recipient or the person responsible for
delivering the message to the intended recipient, you are strictly
prohibited from disclosing, distributing, copying or in any way using this
message. If you have received this communication in error, please notify
the sender, and destroy and delete any copies you may have received.

WSP provides professional land surveying services through the following
entities: WSP Surveys (AB) Limited Partnership and WSP Surveys (BC) Limited
Partnership

Hi Christopher and Nick,

In terms of some more real world examples, we have been working on an
opaque materials database: http://www.lighting-materials.com/ The
website is still a bit in progress, and we are still collecting
measurements, but the goal is to give realizable examples of material
reflectances, especially for unusual materials. And it works right now!

It is relatively easy to find blue colored materials by searching via
color. A quick ordinal diagram is below,

We have also measured several wood surfaces, which you can find by
searching by name for 'wood.' Hopefully this can also help to bracket
your material properties and define some proper R-G-B color combinations
for your scene. There are also a number of white wall surfaces in the
database. By clicking on any of the results, you get more detailed
information including the R-G-B primaries for a physically-based
Radiance material. There is some more information about this undertaking
in the second half of our Radiance workshop presentation

given last month in Philadelphia.

I agree that defining specific textures and wood grains is painful and
difficult to make accurate. In my opinion the texture of the carpet
tiles and the wood surfaces can be ignored unless those aspects will
modify the light contribution significantly. By trying to get this as
correct as possible, you are already doing way more than the average
LEEDv4 lighting simulation, I am certain.

All the best,
Alstan

J. Alstan Jakubiec
Assistant Professor
Architecture and Sustainable Design
Singapore University of Technology and Design
8 Somapah Road, Singapore 487372
telephone: +65 6499 4530, e-mail: john_jakubiec at sutd.edu.sg
Design for Climate and Comfort Lab |
profile | DIVA
| Mapdwell
events: DIVA Day
on
daylighting in design, 22-24 October in London | DIVA Day Student
Competition