Lights in iRay
Kev914
Posts: 1,126
Sometimes how lights work in iRay is a total mystery to me.
I have some light sets that I purchased and when I use them, I try to look at them to see where the lights are and what the settings are. In one light set, the tone mapping was set to 14 and I saw the spot lights were father away than I put them and the settings for the lumious was around the default. So I thought...maybe my lights need to be farther away. So I tried that. I also plugged in one of those HDRI images that I had. When I first rendered, I thought it looked nice, but then after looking at it for a while, I decided that the figure wasn't lit properly. I tried adjusting the tone mapping up and down, but the figure just didn't pop. Finally after a bunch of trial and error, I finally set the tone mapping to 14 to see if my light would have more of an effect. At first I doubled the light setting (luminous), and then I started adding zeroes. I think I ended up with 4,000,000. I had tried 400,000 and it still didn't pop. I figured the 4 mill was going to cause some burn out. But it didn't. My figure looked nice. I could see variations in the skin tone. I could see details on the hands and legs.
But I don't get it, how can a preset light use so low a luminos value and I have to use one so high?
Or are there other settings in play here that I haven't discovered yet?
And what setting do you use to contral how much or how little the HDRI affects the scene?
I also noticed that the back light is often set much higher than the front and fill lights. I would have thought that it would be low. Maybe that has some affect too on how things turn out.
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Comments
What were the units of your lights vs. the preset ones? If you are using cd and they are using kcd or something, that can make a huge difference. Also how far away the lights are has a very big effect.
For HDRI, if you go finite and mess with Dome Size I think that can affect it. I know at one point I had not realized a preset HDRI came in with for some reason a small finite dome, and I was trying to light a scene with the DAZ Dream home and it was just not freaking lighting at all... After playing with it forever I realized the dome was too small... I guess it was "inside" the house so viewing from outside I got almost no light. Making the dome much larger fixed that. So check dome size.
14 tone map seems like a narrow f/stop unless you are simulating full sun. I rarely work that low. For indoor shots, just like with a normal camera, I am usually working at the wider end of the spectrum, e.g. 5.6, 2.8 (from habit I usually use classic camera stops just because I am used to them from photography). For outdoor work under sun/sky or most HDRI settings I am at around f/11. Sometimes I have to go up to 16, but only in very bright sunny HDRI with the sun shining diectly on the figures.
If you Google "Sickleyield" and "IRay lights," you'll probably find some tutorials. Sickleyield's online tuts helped me understand a lot about IRay lighting.
Thanks to both of you. Great tips. I completely forgot about the units setting. I have watched some of Sickleyield's tutorials. I have to search them out and watch them again.
The HDRI can be altered using the Environment Intensity slider above where the Environment Map is, also altering the slider for the Map alters the light
Thanks, Scorpio. I'll try experimenting with those sliders. I think one of the sliders is suppose to alter the direction of the light. Maybe that's what you mean by "alters the light".
I can understand the frustration with iray. I dislike adding so many zeroes to get the lights the way I want them. I tend to not have a good understanding of how much I will need, and it means I spend a fair amount of time adjusting the zeroes rather than enjoying myself. I prefer sort of a percentage dial like there was in 3delight. It was more intuitive for me than iray is.
...I had similar issues with Uber Area lights as well. Seemed I had to use ridiculous values just to mimic a 60 - 100W light source.
Been having issues getting the photometric lights as well. Sometimes I can set them to a "reasonable" intensity and they work fine, then other times I really have to crank them up to totally ludicrous values to get the same effect even when using similar tone mapping settings.
While creating mesh lights using the Emissive shader gives more accurate illumination on a more consistent basis, the shadows produced tend to be too diffuse.
As I used to work with theatrical lighting I find this most vexing. Didn't have these issues with the standard Daz or AoA Advanced lights.
I wish people still did PDF tutorials as I have terrible retention with videos.
For a 3Delight light, there is no such thing as a ridiculous value. The values are totally unitless and have no real world counterparts...so what ever value needs to be put in to make it work is perfectly fine. Some lights come with a scaling factor...some don't. Some have falloff...others don't. A light without a scaling factor but with falloff ON requires what seems to be extremely large values to do anything...but consider that 'realistic' falloff means that 2x the distance from the source = 1/4 the light. And Studio's base unit is the centimeter.
That same pesky 1 unit = 1 cm also plays a role in the seemingly strange photometric light parameter bahavior in Iray, too. Coupled with the base toning mapping being set up for an 'outdoor' shot on a bright, clear day...without an 'auto exposure' settings on the camera. Then there is hte fact that certain units used for lights have little basis to the actual amount of light...namely Watts...I'm sitting here with a 3.5W led that is rated at around 2000 lumens. That's somewhere around a 100W incandescent...
That would be an efficacy setting for the led being around 70 which is within the range for them. Incandescent lights are 15.
Efficacy = lumens per watt
https://en.wikipedia.org/wiki/Luminous_efficacy
I didn't want to get into that...but yeah, that's the 'why'. The point, though, is that without knowing that, entering 3W for a light and expecting around 2000 lumens is not going to get you very far.
At some point, there HAS to some technical learning going...
..which is no doubt why those LED headlights in cars today seem so bloody much harsher than the old sealed beams.
Still wish I could find some "standard" to work with. It all seemed so much simpler with the Daz Default lights. 100% lit up everything bright as day and you reduced the value to suit the needs of your scene from there.
For emissive objects, you can quite easily use (very) low values by changing the units to cd/cm2, which is candles per centimeter square. With this setting, values of 20 to 50 give out loads of light, and the light output per area of the object remains consistent.
For the point and spot light types, there are always in lumens, and yes, the values can sometimes be quite high, because the luminance is for the entire surface; the larger the surface, the higher the numbers will need to be in order to cast a certain amount of light onto an area of the scene. If the big numbers bog you down, create a scene with some lights you like, and save as a preset. With a generic setting you may seldom need to mess with adjusting the luminance value. You can save lights as a set, or individually.
For distant lights, remember the luminance value is candles per square centimeter *incident on the scene*. Therefore, a value of just 9 or10 will mimic noon day sun: there's about 9.3 lumens per square centimeter from the overhead sun at noon.
...however as I mentioned, shadows from emissive lights often tend to be too diffuse. I wish there was a shadow softness/hardness adjustment.
The downside of using Photometric lights (besides the seeming inconsistency in intensity scale) it is having to go back to the tedious 3DL process positioning large arrays of lights in a scene again.
Shadows from nearby, non-point lights will be soft as the amount of the emitter that is blocked will change as the relative position of emitter and shadow source change across a surface. Distant and small sources will product sharper shadows. this is basic geometry and not something that could be changed by a parameter. The 3Delight Shadow Softness setting is faking this effect for point/distant sources.
The trick to Iray lighting (I know, I want to call it 'iRay' too; the actual name always looks too much like 'Tray' to my eye) is that the 'standards' are the real world. For example, if you have a computer monitor emitting light, you can look up the specs (e.g., for the Apple 27-inch Thunderbolt), and find that it has a brightness of 375 cd/m^2. A 100-watt incandescent bulb has a total light output (approximately a sphere) of 1600 lumens, and a color temperature of 2870K. You can google for all these things.
But if I light a room with a sphere with its emissive output set to 1600 lumens, it seems so dark!! The reason is that the Tone Mapping render settings correspond to the settings of a camera, and the defaults are tuned for a bright sunny day. Fortunately, the tonemapping settings are simpler than a camera, because they all get composited into a single number. In a real camera, shutter speed will affect motion blur (but not here), and aperture (f-stop) will affect depth of focus (again, not here). So you can stick with just one of the three knobs and the effect will be the same. Having three knobs, I think, just enables one to use real-world settings as recommended on photography sites. Anyhow, if you crank up the ISO rating from its default 100 to 1000 or 1600 (or even more), your room will be well lit by that 100W bulb.
You can use point-geometry photometric spotlights to get hard shadows - but again, if you're trying for 'photoreal' results, those won't be very realistic. Not even the sun casts perfectly hard shadows, after all (since it has a finite size in the sky).
Basically, with Iray, you have to think more like a photographer and consider what the real-world analogue is for the lighting you want to achieve. And if that turns out to be extremely complicated, perhaps Iray isn't the right tool for the job at hand. On the other hand, real-world photographers set up an awful lot of lights sometimes.
...I used to do "available light" photography using high speed Ektacrhome (ISO 400). Needed one film type for Tungsten light (your "normal" lightbulb) and one for UV light (florescent lights) to get the proper "tone" balance. This is why I preferred Tri-X Pan as it was black & white so lighting type was not an issue. I could pretty much do handheld shots in most normal room lighting conditions (had a pretty steady hand back then) and in lower values if I pushed teh ISO to 600 or even 800. The highest push I did was ISO 1200 with 400 speed Tri-X Pan.
This is sort of where I am coming from when approaching physically based lighting.
The problem with relying on tone mapping to increase brightness is that it does not increase the photonic sampling in the scene, and it's the samples that drive pixel convergence. It's akin to trying to fix a badly exposed picture in Photoshop by messing with the Curves adjustment. Sure, it can improve the image, but it's much better to start with a better picture to begin with.
If you want a good scene, spend the time to light it properly. In the real world, shooting outdoors, we don't usually have the benefit of being able to adjust lighting levels -- that's what existing light is all about. So as a result, we have to compensate by adjusting the camera controls, or using filters over the lens, or by changing the film processing step.
There's no point taking that limitation into a studio where you DO have the flexibility to control the lighting and lighting amounts. Similarly with Iray, it makes no sense to me to throw insufficient light into scene, and then expect to fix it by tone mapping. The tone mapping controls do nothing to alter light levels, and good light levels make for better and faster renders.
As a BTW, the default tone mapping settings are not for a bright day, but for hazy sun to cloudy. A bright sunny day would be f/16 (or even f/22 depending on the film). This would assume close reciprocal settings between shutter speed and ISO.
I tried to understand Iray from the start. I sought every kind of tutorial. Still I think everything is very white, washed, without definition. But is rather a Great Render for those who want a photographic effect of Render.
I always looked for in my Renders something more graphic, even art, with respect, hand painted. And bright colors, a great clarity. 3Delight gives me.
3Delight for a time, worked well on my computer and suddenly, my Studio, sucked all my CPU and I did nothing, not a reder minimum size available. It was the end. So computer, burned on a hot summer too in Brazil. I took over a year to get another computer. Now a powerful computer, which 3Delight, is done in minutes.
Use 3Delight, because I myself putting my lights, my way and manner, the thing is equal or better than Iray.
I believe that everything is a matter of taste.
Do you like photograpy, realism use Iray.
You like illustration, something more artistic is 3Delight.
" Age Of Warriors - Celts 1 " - 3Delight not Photography.
Straight Iray render. No postwork
Personally I find Iray much better for the "painterly" look. Because if there's one thing most of the old masters were really into it was lighting. And Iray is really good at lighting once you have a handle on it.
and below: an image I'm working on with a very marginal amount of postwork (just using the camera raw filter in photoshop)
...I've been using the actual shutter speed/aperture setting tables for various types of real films.
For outdoor daytime scenes my usual choice was Kodachrome or Ektacrhome 64. Fort indoor and night outdoor I used Ekatacrhome 200 & 400 Professional (the latter for available light photography with no flash) or Tri-X Pan B&W. With Luxrender and Reality 2.5 this approach worked pretty well, the only downside being the "glacial" rendering times. Reality 4.0 was a mess with so many bugs and patches that I gave up on it. When Daz intergrated Iray into their Studio application I felt I had a bit of a leg up having worked in a physically based render engine. Now I am not so sure.
Daytime outdoor scenes work OK as I can use the same settings as I would with film and they looked pretty good (though I had to tweak the saturation to get that "Kodacrhome quality"). The nice feature with Reality is it has actual film quality presets one can choose that act just like the real thing, no having to manually adjust saturation, colour balance, or gamma. I would have continued with Reality/Lux were it not for all the stability issues with 4.0 and again, the extreme render times.
When it came to interior and/or night scenes that became far more problematic in Iray than Lux. Settings that I used with film for available light shots didn't work as well as they did. As I mentioned, emissive mesh lights didn't produce proper looking shadows while photometric lights seemed inconsistent as to what values to use even with the same tone map settings.
I would also be using 3DL more had flagging the SSS skin shader with the AoA advanced lights not been broken in the 4.7 update (the Atmospheric and Graphic Art Cameras have since been fixed through third party scripts). After I ditched Reality and before Iray was implemented, I felt I was getting pretty close to a photographic look using the AoA lights, SSS skin shaders and Atmospheric Cameras (the latter which had finer adjustments than the Iray Atmo Cam). Sadly, I couldn't adjust lighting for specular, diffuse, or translucency effects on skin that used SSS as like I mentioned, the flagging for the Advanced Lights was broken with respect to the shader. Going to UE not only involved much longer render times (longer than even Iray in CPU mode), but resulted in higher CPU temps than the default 3DL or Lux during the process.