Soft Light

Soft Lights with by S68 who, in the real word answers to the name of Stefano Selleri www.selleri.org [email protected] 12-03-2002

INTRODUCTION Ok, folks, times for a 2nd tutorial. Paradox showed a vase + lamp scene with very cool soft light and shadows. There was a intense exchange of messages and posts between the two of us, Stonzy and darkelfv which lead to many interesting results. My solution, presented here, is based on the classical Dupliverted spot light but there are some tweaks which might be of interest for the community. The tutorial will be divided into two section: Soft light Indoor and Soft light Outdoor.

Indoor For directional light Indoor a single spot might be enough. In reality it isn't because light never comes from a single point in space but from an object of finite dimension. Hence you need an area casting light. Besides Radiosity, which is cool but slow, you can use a series of spots correctly placed and oriented. I'm talking of spots because I assume you would like to have shadows too, but any light source is good.

This is what you get from a simple scene with a single spot light. It is nice but you can do better. S68 - Soft Lights Tutorial for Blender Page 1/1

First, in top view, create a cylinder, with not too many vertexes, say 12. Then, in side view, select all the vertexes of the upper base and delete (X KEY) them. Go back in top view and add a lamp. Make it a spot with a nice warm light colour. Put the energy down. If with a single spot you need energy ? now you must give to the newly created spot an energy ? / N , being N the number of vertexes of the mesh (here 13). Give to your Mesh (the remaining base of the cylinder) the size you want for your area light. Parent the spot to the mesh (select spot, then SHIFT select mesh, then press CTRL P) then in anim window (F7), with the mesh selected, press 'DupliVerts' and 'Rot' buttons. Now your mesh is an Area Light! Spot softness (SpotBl) should be pretty high, to allow a nice blending of the spots. In this image the value was 0.608. Next step is to place it in the right place and rotates it so that the direction of incidence suits your need.

As you may notice image is a bit darker because spots do not sum everywhere, but lights and shadows are noticeably softer and more good looking. Also specularity highlights on the vase are more diffused and more convincing. Another tweak, to fake area light which comes from a finite distance, is to resort to an UV sphere as a mesh. In top view add a UV sphere with not too many vertexes, say 12 segments and 12 rings. In side view select all the vertexes but the last two rings and the bottom pole and delete them (X KEY). Select the remaining node and constrain scale (S KEY, then press middle S68 - Soft Lights Tutorial for Blender Page 2/2

mouse button) so that mesh is flatter. The flatter the mesh, the more directive the beam. In top view scale once more to the desired dimension of the area light. Next steps are identical as before, except that now you have 25 vertexes and hence energy should be further decreased. This time you came out with 25 spots projecting their beam of light in the direction normal to the (flattened) spherical surface comprising the mesh. The effect is that of a lamp of finite size and distance from the object.

An additional, subtle tweak to better fake radiosity is to place two very dim lamps on each wall, casting a light having the same colour of the wall. This way you'll get both some light illuminating the shaded side of your object and the correct hue.

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Outdoors Suppose now you want to have nice smooth lights and shadows in an Outdoor scene. All the sky diffuses light, so there is a small amount of light coming from each point of the sky, but there is also the sun, unless sky is completely covered with clouds. Again a single spot faking the sun is inappropriate. You don't get the light diffused by the atmosphere.

Your sun is hopelessly a point, not an area light. Shadows are sharp and uniform. The conventional technique to obtain a faked global illumination to approximate atmospheric diffusion is to use the dupliverted spot technique described earlier with a skydome, or, in other words (half) an iconsphere. In top view add an Iconsphere (Subdivisions at least 2, 3 is better). In side view delete all nodes below the horizon. Move iconsphere up so that no vertex is actually on the horizont. Flip the normals (Flip Normals button in F9 window). Back in top view scale the iconsphere so that it will engulf your entire scene. Then add a spot and parent it to the iconsphere. Duplivert and Rot as for previous examples. Result is interesting ad there is a sensation of light coming from every point of the space, but no distinct shadow is present and general feeling is that of a gloomy cloudy day.

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To get rid of this one possibility is to add a single strong Spot light casting light and shadows. The Iconsphere area light can be light blue and the single spot representing the sun sligthly yellow for a better result.

In any case you get again a spot and not an area light, and sun is an area light, otherwise how could we get partial eclipses? So you can add a sun the way we did for Indoor light (a disk coming from a cylinder is better here since the sun is usually quite far away) Or we can think something different. For the lazy ones, once you are done with the half iconsphere stuff you are done! Look at your iconsphere in top view, it is made of triangles, clustered in hexagons or pentagons. Go Editmode (TAB) Choose a vertex where you want your sun to be. Select it and all the vertexes surrounding it and press the subdivide button in the mesh editing (F9) window. Deselect all ad re-select the central vertex and the 6 (5) newly created vertexes surrounding it. Press subdivide again. Repeat the subdivision process as many times as you like - I did it thrice, don't exaggerate, unless you are willing to wait a lot for rendering... This technique is interesting because it actually takes into account that light is diffused by the whole atmosphere but there is more diffused light next to the sun, furthermore the sun itself is an area, not a point. S68 - Soft Lights Tutorial for Blender Page 5/5

Be extremely careful with energy, now you have a lot of spots (If you followed my steps, they are 127) so energy must be really low (I used 0.030). Be also careful with ClipStart and ClipEnd, don't keep ClipStart too close to the spot, move it towards the object. Keep SpotBl fairly high (around 0.6) so that spots blend nicely, but don't bother with Samples and Soft. They are unneeded since it is the number of spots which smoothes shadows. I kept both down to a value of 2.

Conclusions Description of two Soft light scenes, indoor and outdoor has been carried out. I hope that in this tutorial you found some useful tips to get smoot and soft lights and shadows in your renders. Happy Blending Stefano

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