No light from area light portals?

HI,

Sorry if this is a silly question but i seem to have an odd problem.

If i make a scene with the default cube. Add an area light, set the area light size to something like 4 (or any number). Then i click render and there is light!

If i then click the portal button, suddenly there is no light. Is there a render setting i’m not pressing?

Cheers

i believe that you should only check portals for interior scenes. If you check portals on an area lamp, the lamp doesnt function as a lamp no more, but as a guideline to where blender should aim camera rays (i know i sound very vague right now). Take a look at this video: https://www.youtube.com/watch?v=oveSskhIEAc , this guy can explain it way better than me.

So does that mean he had a sun lamp outside and then used the portal area lamp to direct it?

I just tried this, i added a sun lamp and a portal lamp in the window and my scene became more grainy??

Portals only work for environmental light, not regular lights.

If the majority of your noise is from a sunlamp, then they will not help much.

Wonderful, bumped up the environment lighting and added some area lights. Now i have a nice looking scene! much appreciated

HOW??? In blender 2.8 i still cannot make it work T_T GG i have put HDRI and also i try many other way but still not working it emit no light

Portals do not emit light. They “direct” light from other sources.

If you are saying the entire scene has no light at all, check for other things causing it.

I believe (not 100% sure) portals work by guiding rays “looking for light” to the right spot. So if you have a small opening (hide windows as wrong materials can cause issues too), your floor sampling will ask “where are the lights I need to sample”? Portal will say “head this way and you can find a pixel on the environment map or sky texture” behind the portal object. Otherwise it would check in all directions with equal weight (or based on MIS) and have little chance of finding the environment. It’s supposed to have more impact the smaller the opening. Again, turn off the window object in case its glass is causing issues, and make sure the portal is pointing the correct way.
PortalOff:


PortalOn:

HDRI based environment with no denoising. 100 Samples.

It’s not supposed to.

Portals tend to only be of use when you only have 1 opening or of all your openings are very small. In a scene with 6 good sized windows portals don’t do anything to improve my render.

Depends on the situation I guess. It just aids guide the “light lookup rays” to an area of importance. If you had a small skylight entrance in the ceiling and big windows that were prevented to see the environment (i.e. tall solid fencing), I think it would still help the skylight. Being situational, I think best approach is to add them into logical groups, and test how much they matter. So maybe you end up turning them off for big unobstructed windows and leave them on for skylights? Maybe I should look more into them myself as well, I’m basically just guessing here, but it kinda makes sense in my head :smiley:

yes i already put in the environment HDRI in environment world shading. Furthermore i also try adding one sun i just wanna know will that sun is the light that will get directed by the portal light … but nothing is working … i check the whole internet they didn’t talk much about this. Thank you for reply

Wow thank you I really appreciate the fact that you give your time in writing this … i am thankful… yes i will try it again… thank you sooo mucch

No, only the world background shader is affected afaik. If you have large unblocked windows the portal style guidance isn’t really needed - a lot of the background shader is “found” randomly anyway for its direct light contribution. I don’t know how the renderer does it, but it would make sense to me that direct contribution by the sun is traced the opposite way - is there anything blocking the sunlight if I trace the sun vector from the pixel?

I did some tests, and you need to have significantly blocked windows (partial curtains, tall fences, close neighbor house) for portals to have sensible effect on resolving the background shader. If you add a sun to all this in all it’s mighty power (I’m using sun 4500K strength 441 and sky texture 29 strength), it’s likely to drown the contribution from the small openings. The indirect contribution from the sun is going to create a lot more noise than the small openings (at least on fairly bright surfaces). This is from a fairly brute force point of view, in reality you might try to do some fakery and optimizations.