How to calculate lighting power of a textured LEM ?

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derei
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Re: How to calculate lighting power of a textured LEM ?

Post by derei » Wed Jan 29, 2014 6:09 am

Chris wrote:Nice results. :^:

I would be very surprised that light emitting materials change their emission direction based on a normal map. You might be able to use an IES emitting texture though...
As I know, normal maps alter the surface of the geometry, in opposition with bump maps who only alter the perception, the reflection of light on surface.
So, if normal mapping will alter the surface, the resulted indentations would limit the spread angle of light, thus creating a spot-like effect.

I don't know how a IES texture works, even though I'm using IES in Twilight pretty often. I don't know how and if it can be applied to a linear shape. I'm only using IES for Twilight Lights (I set a light, then I load a IES on it).
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Chris
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Re: How to calculate lighting power of a textured LEM ?

Post by Chris » Wed Jan 29, 2014 2:54 pm

I'm not super experienced with IES with a texture either. I'd have to play around with it.

Normal maps don't alter the surface geometry. You are thinking of displacement maps (which Twilight does not support). Normal maps do the exact same thing that bump maps do, they change the direction that light reflects when it hits the surface. They just do it using different information.

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Re: How to calculate lighting power of a textured LEM ?

Post by Fletch » Wed Jan 29, 2014 4:15 pm

I agree with Chris.

Owning several LED strip lights, personally, I can say after close observation the "spot light" effect, light clearly thrown from individual emitters, from each light only exists on surfaces closer than 1.5 inches away from the strip light, and rather, it appears to throw light quite evenly beyond that.

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Re: How to calculate lighting power of a textured LEM ?

Post by Chris » Wed Jan 29, 2014 6:08 pm

I did some test renders (below). IES files combined with textures can definitely produce some cool "character" but I don't think will be able to exactly capture the effect you're looking for. In addition, it might screw up your lighting calculations as IES files correspond typically to specific light outputs. But in cases where it's less important, you can get some great variations. Definitely something to remember for the future.
Attachments
ies1.jpg
ies1.jpg (25.93 KiB) Viewed 10542 times
ies2.jpg
ies2.jpg (22.56 KiB) Viewed 10542 times
ies4.jpg
ies4.jpg (25.8 KiB) Viewed 10542 times
ies5.jpg
ies5.jpg (28.64 KiB) Viewed 10542 times

derei
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Re: How to calculate lighting power of a textured LEM ?

Post by derei » Wed Jan 29, 2014 8:27 pm

I'm sorry to contradict again, but normal-maps DO alter the geometry. And I am not referring to displacement here. Indeed, displacement alters geometry in a drastic manner.
But normal mapping does too. Make a test: render a "moon" sphere. Or any sphere with a heavy normal map, then render it again with a similar bump map. You will see at the edge of the sphere that normal mapping alters its contour, but bump mapping preserve the perfect sphere shape.
As proof, please see this: http://en.wikipedia.org/wiki/Bump_mapping

And about LEDs indeed the spot shape is visible only for close distance, but that is how I need to use it. In the meantime I discovered how to use IES LEM and also I found an IES file for a LED strip (actually is only for a single LED piece, I have to mention that). Also, I learned how to ALTER the IES file, because that file emitted a light equal with a full 5m strip...

I still have a question: if I have INSIDE a component, several rectangles that do not touch each other and I paint them with a LEM, they will be considered THE SAME emitting geometry, or each rectangle will be considered a separate emitter, despite the fact that are raw geometry inside a component?
I know that if I have multiple instances of a LEM component, each one is a different light emitter.
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Re: How to calculate lighting power of a textured LEM ?

Post by Chris » Wed Jan 29, 2014 9:35 pm

Hmm... well, I'm not sure where you saw a normal map modifying the geometry but it doesn't happen using the Kerkythea engine (I wish it did!!).

Here are two images, the edge of a cube and a low-res sphere. Both are using a very drastic normal map. I do not see any change along the contour.
wall.jpg
wall.jpg (80.56 KiB) Viewed 10537 times
sphere.jpg
sphere.jpg (57.19 KiB) Viewed 10537 times
As for you question about the light emitting material: by default, light emitting material uses watts/m^2. So the amount of light emitted by a surface is entirely dependent on the size of the geometry. Whether you have them in a component or out should not change the result. However, you can create a material in KT that uses a total wattage output that is spread evenly across all surfaces using that material. In that case, components do matter. The total wattage will be spread across the geometry inside the component but will not be effected by geometry outside the component or by the number of instances of that component. (I hope that explanation makes sense ;) )

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Re: How to calculate lighting power of a textured LEM ?

Post by Fletch » Wed Jan 29, 2014 9:39 pm

Hi dereei,
I think you are confusing the term Normal Map and Displacement Map.
This is stated clearly even following the link you posted above.
"normal mapping, ...is a technique used for faking the lighting of bumps and dents - an implementation of Bump mapping. It is used to add details without using more polygons." i.e. it is not actually modifying the geometry. While Displacement Mapping uses the image to drive an algorithm that actually creates new polygons/surfaces. Normal mapping is superior to Bump maps in some ways, but a proper normal map is more difficult to produce than a "dumb" bump map. Actually, a "proper" bump map that actually maps the intended displacement is also not easy to generate for complex materials like natural stone.

And, when it comes to discussing materials, whatever Chris says is gold. He's written several programs dealing with materials creation, He has forgotten more about materials in 3D than I will likely ever know. He is, for my money, a "guru" :ugeek: on the topic. :lol:

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Re: How to calculate lighting power of a textured LEM ?

Post by Fletch » Wed Jan 29, 2014 10:45 pm

We are in luck!
Here are Lightolier's photometry files for LED light strips (each strip is 12" long x approx. .75" wide) I will attach the files so that they are not lost in the future when their website changes.

Here you can see my tests for the tell-tale shadow pattern of a strip of small lights. It was to see if the PNG file was actually rendering as small light points, and it IS.
I tested this with the PNG file I linked to above, then again with small light emitting rectangles.

I will try one with the IES file and a warm color, IES set to power 900w/m2.
Attachments
LED-IES-photometric-strip-light-12inch.zip
4w or 6w 2700k warm white LED light strip IES files
(2.81 KiB) Downloaded 559 times
led-light-strip-test.png
led-light-strip-test.png (271.22 KiB) Viewed 10533 times

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Re: How to calculate lighting power of a textured LEM ?

Post by Fletch » Wed Jan 29, 2014 11:52 pm

Here's another test, with a material texture emitter, with the LED spacing at 12". (30cm)
Attachments
12-inch-spacing.jpg
12-inch-spacing.jpg (30.41 KiB) Viewed 10531 times
LED-Strip-Test.jpg
LED-Strip-Test.jpg (21.81 KiB) Viewed 10531 times

derei
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Re: How to calculate lighting power of a textured LEM ?

Post by derei » Thu Jan 30, 2014 6:13 pm

Another test:

Twilight spotlight with IES (on the left) vs LEM with IES (on the right)
IES_Spot vs IES_LEM.jpg
IES_Spot vs IES_LEM.jpg (444.58 KiB) Viewed 10522 times
Also, the geometry of the IES spotlight:
-as Twilight Light Editor doesn't allow smaller light than 2.5mm radius, I scaled the geometry manually inside the component
LED Test Scene.png
LED Test Scene.png (36.49 KiB) Viewed 10522 times
Attachments
FLA-Flex_LED_WP_RGB_mod.7z
IES file that I used for this test
(763 Bytes) Downloaded 547 times
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