Cycles Lighting setup

Hi everyone. I have a texture with alpha channel. (you can see it in the upper corner of the render). I want this texture to cast sharp shadow to the classroom.

Is there a way to adjust Cycles emitter planes to cast less diffused light to make sharper shadows?:spin:

Thanx in advance.

Cycles render is physically based. You need sun light or very distant small emission plain for that, but still you can get trouble because of “direct light” feature, when Cycles shot shadow probe it can ignore complex transparent textures, so it assume whole object transparent or opaque. Simple texture can work.

What do you mean by saying simple texture can work?

Following storm_st advice I’ve managed to archieve this result:

Perforated facade with circles and dots outside of the window was made using jpg texture with B&W stencil.
Important aspect to mention is that transparent shadows appeared only using CPU as rendering power.

Sun lamp worked as light source with it size set to 0.001. There were several emitter planes inside and outside the classroom.

Background was added later with gimp.
Any suggestions for improvement are welcome.

some other shots from the same project.

need advice to light up interior scene with deep space, illuminated mainly with artificial lighting. Everything is OK when there is a window in 2 - 3 meters, but when i need to visualize enclosed scenes there is a lot of noise, like in the example above.

this image was stopped at 500 passes, it is not much, but i discovered that if there is lot of noise after ~100 passes, it won’t disappear even after 1000.

in some cases i avoid ceiling in the composition and make all ceiling emit light. That works fine(clear render), but this angle isn’t suitable for this scenario.

would be great to hear some lighting tips and techniques, thanx.

Cycles sample only 1 light in a turn (random selected), and you have extra noise because you need many samples to smooth that. Try decrease lights count, replace mesh lights with point lights (every mesh light triangle work as another light source). You can decrease physically correctness/unbiasness in a cost of less noise using less (maybe zero?) integrator Max bounce, turn off caustics.

Oh i didn’t even knew that i can use point lights with cycles… tahnx for the tip. It is very helpful, because the light object itself is invisible.

Not sure if Max bounce turned to zero helped though…

thanks a lot, guys! I tried to make vitrage - transparent painted glass, through which light was coming to the temple and setting size to really small value solved problem.
I have a question - is is possible to make beautiful colored light rays visible with Cycles?
It is known as “Volume light” or “Lighting fog”

no spot light yet !

@ Shader2:
No support yet, there is very experimental patch but it so slow you need weeks (literally) to get god rays with moderate noise, months to get average noise-free image.