Lumen Explained - IMPORTANT Tips for UE5

hey everyone welcome back it's great to see you again william foshe here today's video is about lumen now this video may come across as a little wordy long dry and while lumen is fairly user friendly and works very well out of the box there are several changes to the way you need to make your models and materials moving forward so i promise you your work will improve if you just bear with me to the end here this is quite possibly one of the most important videos i've made in a while i know i've made a video about lumen back in may but that video was made three days after ue5 dropped and i've addressed a few issues there but epic has since released additional information making that earlier video a bit outdated somewhat so in this video i've gathered all of the latest and greatest information available most of which gathered from epic's amazing live stream on the topic that said their live stream is over two and a half hours long and while they are gold mines of information a lot of it goes way deeper than necessary for the average artist so that's where this explained series of videos come in i want to condense the info from those live streams into a much more digestible format but before we get started nistito does have a sponsor so let's get that integration done first as to not break the flow of the video later so this video is sponsored by skillshare and as you all know by now skillshare is an online learning platform with thousands of classes for creatives artists or just curious people to explore new skills and dive deeper into existing hobbies or passions if you're curious about virtual production shooting video filmmaking skillshare offered a large variety of classes on cinematography like this short and sweet 30-minute class by zach mulligan called cinematography basics understanding filmmaking which covers the key basics and fundamentals of film the mood the tone and the feel skillshare's classes are curated they have really high production quality they're ad free and there is a constant stream of new classes for you to choose from and since many of you watching this channel are from all corners of the globe it's worth mentioning that skillshare's entire catalog of classes now offers subtitles in spanish french portuguese and dutch now because skillshare is sponsoring this video the first 1000 of you to click the link down below we'll get a one month free trial of skillshare so you can start learning today so once again thanks so much for skillshare for sponsoring this video and with that out of the way let's dive right in starting with the necessary project settings for lumen now by default lumen is active and you don't need to change anything but in the event that you've migrated a ue4 project over to ue5 here's what you need to set it to dynamic global elimination method set the lumen reflection method set to lumen generate mesh distance fields needs to be on in editor lumen is controlled by the following values the light properties the material base color and roughness and the exposure lastly you do have some quality control settings in the post process volume final gather quality and lumen reflection quality which we're going to dive a little bit deeper into real soon next let's talk about what lumen can do the obvious and the not so obvious the obvious being it achieves real-time indirect lighting with rather surprising accuracy and as we all know emissive lighting does contribute to gi just to be clear when i say gi moving forward i mean global elimination so if you have a large bright material it will light up your scene there are several limitations to this which again we will get into a little bit later lumen also provides reflections and integrates gi into the reflections as well so what i mean by this is you will see all of the gi in the reflections this is something that ray trait reflection didn't really do very well in ue4 lumen also supports clear coat materials properly so that there are two reflections not just one which is really useful for car materials again this is something that ray trace reflections really can't do at the moment it also supports fully shadowed skylight so drag and dropping a skylight set to movable will shadow everything automatically with no additional input from the artist it provides a dynamic gi and sky shadowing on translucency and volumetric fog albeit at a lower quality lumen makes things so much easier for artists there's way less fiddling around with hidden settings for lighting and shadow detail most of the heavy lifting is done under the hood which is absolutely awesome for us so how does this all work in pure nerd talk it is a hybrid ray tracing pipeline which uses software ray tracing it traces against the depth buffer first which we call screen traces then it traces against the distance field and applies lighting to ray hits with the surface cache lumen relies heavily on mesh distance fields but what's worth noting here is that the mesh distance fields have been completely rewritten in ue5 for youth with lumens specifically and they are way way better than they ever were in ue4 the mesh distance fields now have mipmaps they're streamed from disk based on distance and they cost about half as much in terms of memory compared to ue4 they also build 10 times faster than before which is a massive upgrade if you remember back in unifor building mesh distance field took a very long time that is no longer the case here now while all this takes care of shadows it can't determine material color and lighting of a surface so that's where the surface cache comes in the surface cache essentially splits up your meshes with a bunch of cards it captures material properties of the mesh color and roughness at very low resolution into an atlas which does work especially well with nanite meshes it also constantly updates its atlas as you fly around your scene it's worth noting however that these recaptures are very slow on non-nanite meshes so if you notice your frame rate just tank for no apparent reason try and see if your environment has some non-nanite models lying around they could be the culprit especially if those meshes don't have proper lods set up you can visualize the surface cache with the following console command right here tldr if you're going to use lumen with any high poly assets they pretty much need to be nanite if you want good frame rates now that was a whole lot of boring talk why should artists care about this crap the surface cache has one major major limitation and this is what's going to affect how you create your assets and your models only simple meshes and interiors can be supported and what i mean by this is you can't simply just use one large combined mesh for an interior for example walls floors ceilings all of these need to be separate individual models if you're trying to light a scene and things just look odd or lighting is only screen space this could be one of the reasons why and while having separate walls and floors and ceilings sounds like a pain in the butt thanks to nanite you can simply bring all of these separate models into a single blueprint asset and from there it's going to be good to go it's a great little trick to combine the convenience of having both a single assembled asset and the quality benefits of lumen the reason i bring this up segues into my next topic the lumen scene which is arguably the most important view mode for lumen because if your lumen scene doesn't roughly match what's on your main screen there's going to be view dependent artifacts in the gi if you've ever noticed that lumens gi is sometimes screen space that is why something is wrong the lumen scene is your number one tool for seeing what is lumen doing why is there an artifact you can maybe compare this between viewports and make sure they look roughly the same lighting wise color wise etc it's really convenient to use the g shortcut especially if you're seeing meshes or objects that are black like this in the lumen scene something is wrong and that object is not contributing to gi black models in the scene means that they are only going to show up in screen traces which is why the lighting will appear and disappear in a screen space fashion but now let's talk about some of lumen's limitations and the very important things to know for now only static mesh and instant static meshes are supported meaning there is no landscape support for this at the moment but it is coming in 5.0 world position offset causes artifacts so anything wind related can be problematic translucent materials are also not yet supported for lumen reflections or dynamic gi so glass is not going to look right the interesting thing is that subsurface scattering does not work with lumen but subsurface profile does it's what i use to give the snow on the ground here a subtle subsurface scattering look lumen also happens to rely heavily on temporal super resolution which is similar to nvidia's dlss this means that it calculates in 1080p and it upscaled everything to 4k resolution all while looking nearly as good as a native 4k temporal super resolution tsr is really the key to making lumen possible in real time lumen does allow hardware ray tracing which offers the highest quality but also the highest cost as well and it only has partial support in early access such as raytrade reflections shadows and it is part of the final gather hardware ray tracing traces against the nanite proxy geometry only so you may need to raise the proxy triangle percent if you're running into artifacts or bad shadows in the nanite settings of a given static mesh if you're using hardware ray tracing try to avoid kit bashing too much or have too many overlapping meshes the performance impact is going to be massive so if you do have a lot of kid bashing maybe stick with software ray tracing instead next when you use the movie render queue you may notice that the first few frames look frankly horrible and noisy and this is because lumen is intended for real time usage and it needs several frames to converge so you need to use a high amount of warm-up frames which you can add here in the movie render queue under the anti-aliasing tab i often use around 250 to 500 warm-up frames just to err on the side of caution it's probably overkill but it works by default the lumen scene is only active to about 200 meters past 200 meters lumen goes screen space so for all intents and purposes you can't really tell because things are so far away at that point but it is worth noting if you're using a very long focal length on your camera that said lumen can be optimized a little bit and the default is to trace mesh distance fields for the first two meters which is detail tracing but you can choose to skip the meshes and field tracing entirely with what we call global tracing this can give you a handy fps boost in scene with a lot of overlapping geo now i've saved one of the major drawbacks of lumen for last and that's the fact that lighting channels are not supported and they won't be supported at all primarily because of how lumen is designed and how it works this really sucks but it is what it is it is a very small price to pay for the incredible lighting that we get now this part here is going to be a favorite for archviz artists you may have noticed that in many cases reflections are just kind of the kind of bleh especially if you're used to the gorgeous sharp and crisp ray trace reflections of ub4 i'm going to tell you all about the magic sauce to get the rage rate reflections and lumen combined together in just a second by default reflections use a surface cache which is great for performance but as you know it doesn't look so hot most people seem to think that you can either use only hardware ray tracing or lumen not both unfortunately you can get the best of both worlds so first open up your project settings and in the rendering section you need to make sure use hardware raytracing when available and support hardware ray tracing are turned on next search for default rhi and make sure this is set to directx 12 then restart unreal lastly you need to set the lumen reflection quality setting in the post process volume to four that is the magic number and that solves our issue now you can get both lumen lighting and rate rate reflection to work together in harmony now for the last part of this video i want to talk about the best practices using lumen so this is a very important part of the video first off you cannot use lumen and emissive meshes to replace light sources you're going to have a bad time if you do results are going to be noisy and inconsistent and possibly even screen space in many cases lumen does pick up emissive materials as we've seen before but the smaller and brighter that emissive source is the noisier the result will be so if you're using emissive materials with lumen keep those sources large and dim for best quality and then go ahead and add an actual light to give your scene the brightness you want use a red light or a point light spotlight whatever just don't rely on only using emissive materials it's going to look bad very small and bright material sources like particles or small lights on the walls of a sci-fi scene are going to be notably problematic next the base color has a huge impact on gi now for those of us coming from an offline rendering or a vfx background this is obvious dark and busy base colors are going to have a poor impact on gi while bright albedo values will bounce the light around more again obviously of course it does but it is important to never use an albedo of one or pure white a perfectly bright albedo means it reflects 100 percent of the light's energy and that simply never happens in real life all surfaces absorb a small portion of light even the purest snow on the top of the himalayas we'll have an albedo 0.8 or 0.9 or so so even though it's very very bright it's still absorbed 10 or 20 percent of the light it's important to keep this in mind when setting up your base colors it's also important to not use a material that's too dark as well and that's just going to suck away all of that lovely indirect lighting in your scene so taking a look at this example right here you're going to see just how impactful a brighter albedo can be again you want to turn on the lumen scene to visualize what's going on in your scene if you have objects that are black or things don't look similar to your main scene here you're going to get screen space gi this is a problem a lot of people have run into and they just write it off at oh lumens of the screen space effect no no it's not lumen is not just screen space but if you're seeing a setup wrong it will be just to give you a classic example in my previous environment i made here i have some snowman from mega scans and they were showing up as black in the lumen scene the reason for this wasn't the model the reason was because of the master material it was using it was by default using the megascan transmission master material as opposed to the default vanilla mega scan material and the transmission one here is the one that broke lumen on these assets that transmission material was automatically created by quixote bridge so pay attention to the materials if not just a mesh that could trigger a black mesh in the lumen scene here like combined walls and ceilings and floors unsupported materials can break lumen 2. so keep an eye on the lumen scene view mode and be sure it stays in sync with your main scene yes these content requirements really suck but it is so much better than authoring light map uvs and baked lighting god i hate baked lighting that would painful and that's it for today folks thank you so much for watching if you did find this video helpful do consider subscribing and hitting the like button down below and as always happy rendering

Channel: William Faucher

Views: 18,134

Keywords: UE4, Unreal Engine 4, Unreal Engine, Cinematics, 4.26, UE4 4.26, UE5, Realtime, realtime rendering, rendering, CGI, 3D, 3D Artist, lumen, Unreal Engine 5, Lighting, tips, tutorial

Id: 1e6oOiKh91U

Length: 16min 2sec (962 seconds)

Published: Thu Dec 16 2021