LEM lights

[Deltronics]

Hello there,

I'm new at this Forum and just starting with Kray, in Lightwave.
I read a lot about LEM lights.
What is that? Is that the best way to render faster or i better use lights?
Can anyone attach a scene with LEM lights, so i see the specs?
The more information about using Kray, the better
Thank you very much.

[thomas]

Hi Deltronics!

Welcome and congratulations on choosing a GREAT render engine! You'll find that the forum here is very friendly and helpful, so fire away your questions.

LEM means Light Emitting Material, or something like that. You can have 2 sources of light in LW or Kray (or other render engines), or let's say 3 sources:

1) Lights, like an area light, distant light, point light, IES light etc...
2) Light emitting geometry (meaning polygons from a 3D model that has more than zero percent luminosity) - this is LEM.
3) Light from a (textured) environment. You could see this as a very big sphere with normal pointed inward around your scene, with a luminous surface in either a solid color, or a texture like a HDR map of a sky.

I'll prepare and upload a scene with a LEM light in a sec.

[Janusz Biela]

Also:
- LEM as interpolated source of light can be used in hundreds shapes and power in one scene and still render will be fast
- LEM has behavior of physical Light Inverse Distance (similar like Area Light)
- LEM has no noise (because this is interpolated source)
- LEM can be totally hidden in scene expect light (behavior of Area Light)
- LEM doesn't give specularity


Here how hide LEM in Kray (LW+Kray GUI, both must be setup) In Kray you must select: Unseen by rays cast light. In Lightwave must be selected: Unseen by Rays and Camera.

and basic scene:

LEM.lwo

(1.01 KiB) Downloaded 812 times

LEM.lws

(18.76 KiB) Downloaded 787 times

Of course LEM never will have Area Light shadow quality (because is interpolated) but it can be enough close to get acceptable effect.

[thomas]

Hi!

Okay,

Here's a scene lit with two area lights and irradiance caching turned on. Irradiance caching is a "smart" algorithm. It calculates the most important defining lighting and shadow points (simple explanation) and fills in the space in between with smooth, interpolated results. This is faster, but comes at the expense of some precision, mostly in the contact shadows.

Next is the same scene but lit with two luminous polygons instead of the area lights. Here the luminous polygons are visible, like two big rectangular lights at the ceiling. In a sense, this is more realistic than the previous render, because in the previous render the light came "from nowhere", where here you have a visible light source. Don't worry, we're going to hide these later! This image is also done using irradiance caching. You'll see that you lose some shadow detail at the legs of the furniture on the floor, and on the wall behind the paintings.

Now we'll do the same render, but turning of irradiance caching. As I said above, irradiance caching was "smart", by sampling the light at the most relevant points, and smoothing out inbetween. When you turn off irradiance caching, we call this mode QMC or quasi-Monte-Carlo: this is a "stupid" or "brute force" method: the lighting is calculated for each individual pixel! This is much more precise or exact, but it is a) slower and b) give noisy results instead of smooth results. The more rays you fire to define the light and shadow, the less noise, but the longer the render takes. (for the record, the QMC method gives you the best results if you have the time, with LW lights or with LEM polygons). You'll see that the contact shadows of the furniture legs and painting are very good, but a bit noisy.

And lastly, let's hide the big LEM polygons and turn up the QMC quality. Hiding is done by going to object properties and unchecking "seen by camera" and "seen by rays" on the object - you need to put the LEM polys in a separate object. By the way, you can of course set different colours and strength of luminosity on different LEM polygons. Then you need to tell Kray that even though the LEMs are hidden, you still want to use them to light your scene, by going to Kray's "Misc" tab and checking "Unseen by rays casts light". In this render I've set the "Min Rays" and "Max Rays" on the Final Gather tab to 200 and 1200 to get less noise.

Lastly, here are my scene files!

http://we.tl/i4eQvql9eH

Good luck!
Thomas

[Deltronics]

Thanks all!
This really helps a lot for now!
I'm gonna practice some more.
I will have some more questions ...................i figure

[thomas]

The fastest way to learn: post your work to the forum and ask for feedback and critique!

Also, looking back at my own progress, I'd advise you to learn how to work with nodes as soon as possible (if you don't already). Once you work with nodes, you never want to go back.

[Keraressi Abdelkarim]

The fastest way to learn: post your work to the forum and ask for feedback and critique!

Also, looking back at my own progress, I'd advise you to learn how to work with nodes as soon as possible (if you don't already). Once you work with nodes, you never want to go back.

can u show me what is big diffeent btw node and basic surfaces editor pls ?!!! .


i want to see 2 render side by side and one scn put ur node and other one put basic surfaces

and if you are not familiare with basic surfaces editor put the scn and file im gonna make the setup cause i use only basic surface editor and we will see the differnt THANK YOU!

[vgabex]

This node or not to node thing reminds me about the SEX. You can live without it, but after you've tried, you'll want it. Everybody should try "nodes"

[thomas]

Hi Lightwave3d (and others),

I'll try to cook up something tomorrow. The difference is not in the basic quality of shaders at the start, because the quality is of course very very similar. But when you build more complex stuff you can do things that are impossible or very impractical with the surface editor. This allows you to build better shaders or render faster.

Also, a lot of the good shading plugins only exist as nodes, so there is a lot of stuff that doesn't exist inside the surface editor.

[Keraressi Abdelkarim]

Hi Lightwave3d (and others),

I'll try to cook up something tomorrow. The difference is not in the basic quality of shaders at the start, because the quality is of course very very similar. But when you build more complex stuff you can do things that are impossible or very impractical with the surface editor. This allows you to build better shaders or render faster.

Also, a lot of the good shading plugins only exist as nodes, so there is a lot of stuff that doesn't exist inside the surface editor.

Sir thank u for this good explain i cant wait to see .

[thomas]

Hi there,

Especially for Lightwave3D as I promised a very quick and rough example of what nodes can do that normal texture layers can't: a sort of carpaint material!

Of course this is just a quick and dirty setup, but it shows how you can have a material with a specific IOR (going to a fresnel shader) that has a very wide and blurry reflection, and on top of that you have a second coating with another IOR and glossy reflection. I'm a bit short on time, but I tried experimenting with the flakes procedural in the nodes, and you can get cool metallic flake reflections with not too much effort as well.

Not the most beautiful render in the world, I know, but it's just a demonstration of how nodes give you more control than then normal texture editor.

[thomas]

Ugly flakes example added here - I made the flake scale too big on purpose so you could see it more easily, of course it looks bad, but it shows the principle. Here the flakes are only changing the amount of reflection - a better way would be to change the normal angle, probably, to get shimmering light effects.

Anyway, with the nodes you can do just about anything you want...

[Keraressi Abdelkarim]

stuning first 2ball awesome shader ur node and let us learn from it :*

[thomas]

I'll try to post an explanation and the shader tonight! Glad you like it!

[Keraressi Abdelkarim]

wow thank u dudde stuning .