# Calculating luminance of surface

We are working on our master thesis at Lund University about Glare from reflections on PV panels. To evaluate whether glare occurs or not, we need the luminance of the reflection on the surface the PV panel reflects light on. However we only get the illuminance of the sun (light source). How can we translate the illuminance from the sun to the luminance of the surface? There has to be a way since we can get the luminance via simulations, however we are interested in a way to calculate the luminance. We also have to take into account that PV panels are neither perfectly specular nor perfectly diffuse.

Best regards,

Erik Hjorth and Florian Wochele

The quantity you are asking for, luminance as a function of incident illuminance, is precisely what the BRDF (bidirectional reflectance distribution function) tells you. If you have the BRDF of your panel, you can compute the luminance directly from illuminance and incident direction. If you do not, you cannot compute the luminance without making some (likely wrong) assumptions.

-Greg

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From: Florian Wochele <[email protected]>
Date: March 3, 2017 1:24:56 AM PST

We are working on our master thesis at Lund University about Glare from reflections on PV panels. To evaluate whether glare occurs or not, we need the luminance of the reflection on the surface the PV panel reflects light on. However we only get the illuminance of the sun (light source). How can we translate the illuminance from the sun to the luminance of the surface? There has to be a way since we can get the luminance via simulations, however we are interested in a way to calculate the luminance. We also have to take into account that PV panels are neither perfectly specular nor perfectly diffuse.

Best regards,

Erik Hjorth and Florian Wochele

Florian,
You might find something useful in Alston's study of disability glare from PV panels:

Andy

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On Mar 3, 2017, at 10:21 AM, Greg Ward <[email protected]> wrote:

The quantity you are asking for, luminance as a function of incident illuminance, is precisely what the BRDF (bidirectional reflectance distribution function) tells you. If you have the BRDF of your panel, you can compute the luminance directly from illuminance and incident direction. If you do not, you cannot compute the luminance without making some (likely wrong) assumptions.

-Greg

From: Florian Wochele <[email protected]>
Date: March 3, 2017 1:24:56 AM PST

We are working on our master thesis at Lund University about Glare from reflections on PV panels. To evaluate whether glare occurs or not, we need the luminance of the reflection on the surface the PV panel reflects light on. However we only get the illuminance of the sun (light source). How can we translate the illuminance from the sun to the luminance of the surface? There has to be a way since we can get the luminance via simulations, however we are interested in a way to calculate the luminance. We also have to take into account that PV panels are neither perfectly specular nor perfectly diffuse.

Best regards,

Erik Hjorth and Florian Wochele

_______________________________________________
[email protected]

Hello Greg,
unfortunately we don't have the BRDF (at least not yet). What kind of assumptions are you talking about? Maybe we can still use the solution in reference to those assumptions.
/Florian

···

Am 03.03.2017 um 19:21 schrieb Greg Ward:

The quantity you are asking for, luminance as a function of incident illuminance, is precisely what the BRDF (bidirectional reflectance distribution function) tells you. If you have the BRDF of your panel, you can compute the luminance directly from illuminance and incident direction. If you do not, you cannot compute the luminance without making some (likely wrong) assumptions.

-Greg

*From: *Florian Wochele <[email protected] <mailto:[email protected]>>

*Date: *March 3, 2017 1:24:56 AM PST

*

We are working on our master thesis at Lund University about Glare from reflections on PV panels. To evaluate whether glare occurs or not, we need the luminance of the reflection on the surface the PV panel reflects light on. However we only get the illuminance of the sun (light source). How can we translate the illuminance from the sun to the luminance of the surface? There has to be a way since we can get the luminance via simulations, however we are interested in a way to calculate the luminance. We also have to take into account that PV panels are neither perfectly specular nor perfectly diffuse.

Best regards,

Erik Hjorth and Florian Wochele

_______________________________________________
[email protected]

Florian,
As a placeholder, until you have a BRDF, you could use data from table 1 of
Alson's paper I sent previously or possibly the angular reflectance and
roughness in Sandia's SGHAT technical reference (section 5.3 and 5.4):

Andy

···

On Mon, Mar 6, 2017 at 1:20 AM, Florian Wochele <[email protected]> wrote:

Hello Greg,
unfortunately we don't have the BRDF (at least not yet). What kind of
assumptions are you talking about? Maybe we can still use the solution in
reference to those assumptions.
/Florian

Am 03.03.2017 um 19:21 schrieb Greg Ward:

The quantity you are asking for, luminance as a function of incident
illuminance, is precisely what the BRDF (bidirectional reflectance
distribution function) tells you. If you have the BRDF of your panel, you
can compute the luminance directly from illuminance and incident
direction. If you do not, you cannot compute the luminance without making
some (likely wrong) assumptions.

-Greg

*From: *Florian Wochele <[email protected]>

*Date: *March 3, 2017 1:24:56 AM PST

We are working on our master thesis at Lund University about Glare from
reflections on PV panels. To evaluate whether glare occurs or not, we need
the luminance of the reflection on the surface the PV panel reflects light
on. However we only get the illuminance of the sun (light source). How can
we translate the illuminance from the sun to the luminance of the surface?
There has to be a way since we can get the luminance via simulations,
however we are interested in a way to calculate the luminance. We also have
to take into account that PV panels are neither perfectly specular nor
perfectly diffuse.

Best regards,

Erik Hjorth and Florian Wochele

_______________________________________________

_______________________________________________