Question regarding the glass material

radiance-general
1

Hello

For my company we are currently trying to simulate the effect of different types of tinted glass when used for solar cells. For that we need to model the glass materials with their proper colored tint.

At the moment we’re having trouble to do this within radiance.
If a simple transparent piece of glass is defined as follows:

void glass transparent
Ø
Ø
3
1 1 1

Now, my question is, how would we then define white or light gray tinted glass materials?
Given that the color code for light gray in percentile RGB is: 0.827 0.827 0.827, would the material in radiance then be:

void glass light_gray
Ø
Ø
3
0.827 0.827 0.827

I would be grateful to hear your thoughts upon this.

Thanks in advance!

Regards,
Olivier Dupon

2

Hi @Olivier,

When you present the value 0.827, do you mean to say that 82.7% of light hitting the glass is going to pass through it? Or are you saying that under certain lighting conditions, the appearance of the glass is the same as the appearance of an RGB=(0.827 0.827 0.827) object drawn on your computer screen? If the latter, this will be very difficult to figure out, as it will depend on the lighting in the room. If the former, you just need to convert the transmittance of the glazing (0.827) to transmissivity (which is what Radiance uses for glass materials), using the following formula from the Radiance reference manual:

transmissivity = (SQRT(0.8402528435+0.0072522239*transmittance^2)-0.9166530661)/0.003626119/transmittance

1 Like
3

Hello @Nathaniel_Jones,

Thanks a lot for answering. It’s indeed the former application we’re trying to implement, so your explanation helps a lot! We were wondering though if by any chance you knew where Radiance has referred this formulation from. Just so that we can cross-check.

Kind regards
Olivier

4

This is rearranged from Fresnel’s equations, which are well-known. The more complete version is in the file ray/src/cal/cal/trans.cal that includes the index of refraction, assumed to be 1.52 in the documentation Nathaniel refers to (the “glass” primitive entry in the Radiance reference manual).

Cheers,
-Greg

5

Regarding reflections from PVs check out Roland Scheckles presentation at the radiance workshop in Loughborough in 2018.

6

Jakubiec and Reinhart also did some good work on the PV module glass materials, using ashik2 and pucker.cal to approximate the beam spread. Two of them can be found at the spectraldb. These are useful for reflection only, however.

void texfunc pucker
6 puck_dx puck_dy puck_dz pucker.cal -s 4.0
0
1 0.0035

pucker ashik2 motech_pvcells
4 0 1 1 .
0
8 0.014864952 0.01887973 0.040865004 0.040973486 0.041036951 0.041638971 100 10