[Radiance-general] displays

[Thomas Bleicher]

Hi Chris.

Because no one answered this so far I will step in with
my limited knowledge and experience about materials:

On 9 Aug 2006, at 10:31, Chris Foster wrote:

> i want to shine light onto an ON display and measure the
> combined light reflecting off of it. this has to include
> the reflected light and the transmitted light of the display
> itself. how do i achieve this?
>
> im comfortable with using rcalc|rtrace|rcalc and bgraph so
> i dont need any help there. i require some assistance with
> the materials for the display. i currently have the material
> LIGHT emitting from one side of the display, would it be wise
> to put in GLASS in front of this light?

You definitively want to combine your light material with
something in front of it as "light" (or "glow" as far as
it matters) has no reflectance and no transmittance. Nothing
will reflect off a "light" and nothing will shine through.
The 'shine through' is what "illum" was designed for.

'glass' as a reflector would certainly be possible but it
is not the best choice. Even if there are still glass-screened
displays around they would probably be treated with some
sort of coating to avoid reflections which the 'glass' material
does not account for.

I'd try a 'trans' material with a very high transmittance
(similar to glass) and nearly no diffuse component. This
gives you the possibility to tweak the reflectance to something
similar to a LCD screen. I don't know what their physical
reflectance value is in reality I just know that I can't read
my screen at work sometimes because I've the window in my
back.

> can i model this glass so that it transmittes the light
> coming from behind it (from the display) and at the same
> time reflects the light incident on it from the front,
> from the spotlights.

Reading the above you might just want to simulate the
glare effect of a point light source on your screen.
Then a 'mirror' type material may be your friend. Just
use your 'light' material as modifier of the mirror for
non source rays:

void light display_light
0
0
3 2.23 2.23 2.23

void mirror display_surface
1 display_light
0
3 0.8 0.8 0.8

(example for something with 80 % reflectance).

You can't change the surface finish, though.


Thomas