uplighting

[super gnu]

i have literally lost count of the number of times ive been asked to uplight or wash a feature wall or similar, with a thin led strip or spotlights, placed really close to the wall that is being uplit. often touching.


what the client wants, is a nice soft wash of light, spreading, often metres, up a wall.


i have never managed to achieve this effect in a "physically correct" way.


i always end up using large hidden plane lights, or self illuminated panels, placed further away from the wall, or sometimes just the gradient tool in photoshop.



with it modelled accurately to the plans (i.e thin led strip within cm of the wall) , i always end up with an ugly line of thermonuclear bright light just above the uplight, and almost no lighting further up the wall.


i know that walls are often lit with setups like this, so why is it so hard to achieve in 3d? is it a material issue? love to know how to get it to work.

[Morne]

I've had some milage with this by enabling the direction parameter of the VRayLight. Make the beam so thin that it just catches the wall and rotate the light as needed. Make just bright enough so you can see it. Then add this light to a light select and deal with it further in post. Sometimes doubling or trippling up the layer in photoshop with different layer blend modes.

[Mokiki]

I had the same issues on a project last year. I had the specific IES lights the client wanted and a lot of reference shots but I never really got the same light coverage of the real one. It always ended too soon.

[crazy homeless guy]

"physically correct"

Vray is foremost a biased engine, therefore not physically correct. I would be curious to see how an unbiased engine would handle this.

[tricky]

We come across this too all the time. We are working on a prestigious project at the moment - lots of classical detailing - and we need to uplight the facade. We are using ies lights at the moment but never achieve great results. We generally fudge it in post.

[AlexP]

Have cheated this in the past using a gradient ramp to blend between original/lighter versions of the material, combined with the actual light you can often get decent result.

Obv depends on the object you are uplighting.

[Rens]

You could try tonemapping, that might help to smooth out the light gradient.

Vray is foremost a biased engine, therefore not physically correct. I would be curious to see how an unbiased engine would handle this.

I doubt there would be any noticable difference in this case, just that it's biased doesn't mean it renders incorrectly (just quicker ).

[super gnu]

yeah i usually tonemap my images somewhat, but really extreme corrections would be needed to get this working as clients tend to like.

in that case i guess post is the way to go. i just wonder if its some property of real world materials, (micro surface details that catch the glancing light etc.. ) which i am missing, and in this case are having a massive effect...



or, of course, it could just be clients being clients and wanting their designs to work like in their heads. maybe a nice wide wall wash really is only possible with more distant/larger uplights.


i say this now as searching google for "wall wash led strip" shows a crapload of walls with a bright hotspot along the base and practically no light further up.


photoshop here we come

[Rens]

You could also try a value of 0.2-0.4 for (diffuse) roughness for you wall material, might make a difference, and in general it's good to have for rough flat surfaces as it balances out the light better between low and high light angles. : )