glare on monitor screen


#1

Dear all,
   
  I have some monitor screens facing quite big window. Therefore, there may be glare occured on the monitor screens. I would like to study this through radiance. I wonder how to model the monitor screen in radiance (what material, what reflectance?) and what glare assessment should be used (dgi?ugr?cie?or others?)
   
  Thank you very much. I really appreciate your help.
   
  Best regards,
   
  Yuni

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#2

Hi Yuni,

Here is a description for an HP LCD monitor we measured at LBNL for the New York Times (work sponsored by NYSERDA). You can substitute any 1024x768 screen shot you like for "VDTdisp.pic". Make sure the maximum value is <= 1.0.

As for glare analysis, I don't know how you mean to associate discomfort glare with a VDT. Perhaps you are thinking of veiling glare -- reflections from the screen that reduce visibility?

-Greg

VDThead.rad (8.14 KB)

VDTon.rad (297 Bytes)

VDTscreen_on.rad (627 Bytes)


#3

Hi Greg,
   
  thank you for your quick reply and your attached LCD info.
   
  Yes correct, I am thinking of veiling glare on the screen that will reduce visibility. Before I received your email, I tried mirror as LCD material. Surely, there is glare (as shown in file.pic), but when I calculate all glare parameter in radiance (dgi, ugr, cie, and others) the results are 0. May be those parameter cannot be used to calculate veiling glare on monitor screen? (high contrast occur vertically on the screen)
   
  Thank you very much, Greg.
   
  Best regards,
   
  Yuni

  Hi Yuni,

Here is a description for an HP LCD monitor we measured at LBNL for
the New York Times (work sponsored by NYSERDA). You can substitute
any 1024x768 screen shot you like for "VDTdisp.pic". Make sure the
maximum value is <= 1.0.

As for glare analysis, I don't know how you mean to associate
discomfort glare with a VDT. Perhaps you are thinking of veiling
glare -- reflections from the screen that reduce visibility?

-Greg

···

"Gregory J. Ward" <gregoryjward@gmail.com> wrote:

From: erika yuniarti
Date: July 25, 2006 10:17:18 AM PDT

Dear all,

I have some monitor screens facing quite big window. Therefore,
there may be glare occured on the monitor screens. I would like to
study this through radiance. I wonder how to model the monitor
screen in radiance (what material, what reflectance?) and what
glare assessment should be used (dgi?ugr?cie?or others?)

Thank you very much. I really appreciate your help.

Best regards,

Yuni

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

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#4

Hi Yuni,

Discomfort glare and reflected glare off a VDT screen are very different, which is why using findglare doesn't tell you anything. The contrast lost on a VDT due to reflected glare is a little tricky to measure, and there are no corresponding standards. You can think of the contrast as the difference between the foreground and the background divided by the adaptation luminance (usually the same the background):

  Contrast = (L_fore - L_back)/L_back

Since reflected glare increases foreground and background equally, the new contrast becomes:

  Contrast_veil = (L_fore - L_back)/(L_back + L_veil)

The larger the veiling luminance, the lower the contrast. Does this make sense?

-Greg

···

From: erika yuniarti <erika_yuniarti@yahoo.com>
Date: July 25, 2006 11:19:44 AM PDT

Hi Greg,

thank you for your quick reply and your attached LCD info.

Yes correct, I am thinking of veiling glare on the screen that will reduce visibility. Before I received your email, I tried mirror as LCD material. Surely, there is glare (as shown in file.pic), but when I calculate all glare parameter in radiance (dgi, ugr, cie, and others) the results are 0. May be those parameter cannot be used to calculate veiling glare on monitor screen? (high contrast occur vertically on the screen)

Thank you very much, Greg.

Best regards,

Yuni


#5

Hi Greg,
   
  Thank you for your quick reply.
  I see, so I could not use "findglare".
   
  is L_fore the luminance of the monitor screen? is L_back the luminance of the surroundings? So you suggest to compare brightness of the monitor screen against brightness of the surrounding?it that so,what contrast level is acceptable?
   
  However, usually, veiling glare on monitor screen causes very bright portions on the screen that the display on the monitor cannot be seen anymore. Isn't it a brightness comparison between areas on the monitor screen it self (instead of brightness comparison between the screen and the surrounding). Or is it not a matter of brightness comparison, instead it is a matter of too much luminance on the screen that we cannot see clear image anymore? If that so, how to get the luminance values occured on the screen (besides the iso contour and false color, because they dont really show value)?

  Many thanks, Greg.
   
  Best regards,
   
  Yuni
   
  Hi Yuni,

Discomfort glare and reflected glare off a VDT screen are very
different, which is why using findglare doesn't tell you anything.
The contrast lost on a VDT due to reflected glare is a little tricky
to measure, and there are no corresponding standards. You can think
of the contrast as the difference between the foreground and the
background divided by the adaptation luminance (usually the same the
background):

Contrast = (L_fore - L_back)/L_back

Since reflected glare increases foreground and background equally,
the new contrast becomes:

Contrast_veil = (L_fore - L_back)/(L_back + L_veil)

The larger the veiling luminance, the lower the contrast. Does this
make sense?

-Greg

···

"Gregory J. Ward" <gregoryjward@gmail.com> wrote:

From: erika yuniarti
Date: July 25, 2006 11:19:44 AM PDT

Hi Greg,

thank you for your quick reply and your attached LCD info.

Yes correct, I am thinking of veiling glare on the screen that will
reduce visibility. Before I received your email, I tried mirror as
LCD material. Surely, there is glare (as shown in file.pic), but
when I calculate all glare parameter in radiance (dgi, ugr, cie,
and others) the results are 0. May be those parameter cannot be
used to calculate veiling glare on monitor screen? (high contrast
occur vertically on the screen)

Thank you very much, Greg.

Best regards,

Yuni

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Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

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#6

Sorry, I should have explained better. L_fore is the luminance of the character or whatever it is you are trying to read. L_back is the luminance of the surround -- on the monitor, not behind it. L_veil is the *additional* luminance caused by unwanted reflection off the screen. You may have to render the monitor with it switched off to get this value. You can use the attached VDToff.rad file for this. You'll also need the other files I've attached, which I forgot in the first posting.

-Greg

VDToff.rad (299 Bytes)

VDTscreen_off.rad (309 Bytes)

VDT.mat (418 Bytes)


#7

Hi Greg,
   
  Thank you for your very quick reply.
   
  I am affraid I cannot understand how to use those files you sent. I am not that advance. I have build a plane as my monitor screen. I dont know how to apply material for this plane. Could you please kindly explain how to apply them in this monitor screen plane?
   
  Many thanks,
   
  Yuni

  Sorry, I should have explained better. L_fore is the luminance of
the character or whatever it is you are trying to read. L_back is
the luminance of the surround -- on the monitor, not behind it.
L_veil is the *additional* luminance caused by unwanted reflection
off the screen. You may have to render the monitor with it switched
off to get this value. You can use the attached VDToff.rad file for
this. You'll also need the other files I've attached, which I forgot
in the first posting.

-Greg

···

"Gregory J. Ward" <gregoryjward@gmail.com> wrote:

From: erika yuniarti
Date: July 25, 2006 6:09:08 PM PDT

Hi Greg,

Thank you for your quick reply.
I see, so I could not use "findglare".

is L_fore the luminance of the monitor screen? is L_back the
luminance of the surroundings? So you suggest to compare brightness
of the monitor screen against brightness of the surrounding?it that
so,what contrast level is acceptable?

However, usually, veiling glare on monitor screen causes very
bright portions on the screen that the display on the monitor
cannot be seen anymore. Isn't it a brightness comparison between
areas on the monitor screen it self (instead of brightness
comparison between the screen and the surrounding). Or is it not a
matter of brightness comparison, instead it is a matter of too much
luminance on the screen that we cannot see clear image anymore? If
that so, how to get the luminance values occured on the screen
(besides the iso contour and false color, because they dont really
show value)?
Many thanks, Greg.

Best regards,

Yuni

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

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