Do you leave a light's Luminous Flux at default, and instead light up your scene with Tone Mapping?

Flortale

Do you leave a light's Luminous Flux at default, and instead light up your scene with Tone Mapping?

I just saw an interesting technique to light a scene.  The scene had a single point light, and it's Luminous Flux was left at the default of 1500.  Then, to light up the scene, Tone mapping was used instead, particularly the Exposure Value, Shutter Speed, and Film ISO settings.

Are we not supposed to crank up the Luminous Flux light setting to insane values like 500,000 or 1,000,000, and instead use Tone Mapping? What's the professional way to light a scene with Point, Distance or Spot lights? Leave Luminous at default value and use Tone Mapping, or leave Tone Mapping alone and rely purely on Luminous Flux?

Richard Haseltine

You don't hae to leave the light at default, but I would usually aim to use a plausible value for whatever the ligh was and adjust Tone mapping as would be the case with a camera (though with DS cameras it makes no functional difference which setting - ISO, f-stop, or speed - you use) to get the desired look. It's a mantra that Iray likes light, but that's more a matter of making sure there is direct light on as much of the scene as possible rather than of ramping up the lvel of the lights.

AlmightyQUEST

I usually change the units on elusive surfaces so at least those values aren't such large numbers to work with when tweaking them. Otherwise I set the lights first, and use exposure settings to refine it. In my case there are usually multiple lights sources (if it isn't an outdoor scene using an HDRI only), so the light sources are going to be different strengths. Knowing how to use the exposure settings, especially for low light and indoor scenes, helps a lot to keep from setting lights too bright, even if you are also changing the default light settings.

Luciel

Professional photographers (and me) typically use much more light than would look natural. This is for a few reasons though both practical (more light means higher shutter speed (less hand shake/movement blur) and less ISO, which means less sensor noise in an actual camera) that don't apply in renders, and stylistic. 

You also have to remember than a light's 1500 lumens is 1500 lux (brightness) spread over the entire area of the light. A 1500 lumen light will deliver 1500 lux to a 1m square area but will only deliver 15 lux to a 10m square area. So the spread angle of a light will decrease the useful brightness, as will the distance (as it's more spread). So it's more than likely you'll need to increase the lumens significantly to compensate. To put it another way, to deliver 500 lux (the typical lighting for an office) to a 10x10m area, you'll expect to need at least a 50000 lumen light.   

Various real world lights deliver 30,000/60,000 lumens+ way over the standard DAZ light's 1500 because of distance/spread factors/lighting needs. Bright sunlight can be 100,000 lux, so 1,000,000 lumens to replicate bright sunlight isn't that unusual. 

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I always lock the exposure value at it's default (the padlock icon) and adjust the shutter speed. ISO is the speed at which the chemicals in film react to light, which is dependant on the grain size of the crystals (silver salts in BW), generally I just ignore it, it does not give me the same effect as real film, that can be done in photoshop. Not sure if ISO actually changes anything.

The lumens has a cd/m2 and a kcd/m2 units setting for lights, extra insane values.

maclean

The default Tone Mapping value of 13.0 is for a bright cloudy day, so you should always change it to suit the type of scene - indoors, night, etc. Ramping up the value of every single light defeats the object of having Tone Mapping available. Individual light values can be increased, but there's no need to multiply them all by 50 or whatever. That's what Tone Mapping's for.

https://en.wikipedia.org/wiki/Exposure_value#Tabulated_exposure_values

Paradigm

I've literally never touched the flux setting. I always use ISO or add more light

barbult

My understanding is that Tone Mapping doesn't really add light to the scene, though, from the point of view of the render engine.  Yes, you can use Tone Mapping to make your rendered image darker or lighter, but Tone Mapping is just post processing, similar to changing curves or levels in Photoshop. I don't think changing Tone Mapping has any affect on how fast an image will render. Does anyone have evidence to the contrary?

marble

For interior scenes (most of my scenes are interior) I generally use a combination of Ghost Lights and Spotlights. Ghost Lights are adjusted in the Surfaces panel and the Spotlight is the one I change the Luminous Flux value. Default is 1500 and I multiply that by 100 to 150,000. I make sure that the camera headlight is off too. Obviously, the 150,000 can change depending on the lighting I want so I go down as far as 50,000 and perhaps up to 200,000. Sometimes I tinker with the Tone Mapping too but not often.

Lastly, I occasionally use HDRi to light interiors either by making some walls/ceilings invisible or by using IRay Section Planes.

Mattymanx

barbult said:

My understanding is that Tone Mapping doesn't really add light to the scene, though, from the point of view of the render engine.  Yes, you can use Tone Mapping to make your rendered image darker or lighter, but Tone Mapping is just post processing, similar to changing curves or levels in Photoshop. I don't think changing Tone Mapping has any affect on how fast an image will render. Does anyone have evidence to the contrary?

As I understand it, you are correct and have summerized nicely.

Sevrin

There are lots of ways to skin the lighting cat.  You can also turn tone mapping off entirely for rendering, assign your lights to canvasses and then do all your final lighting adjustments in post.  If you are comfortable with compositing in an image editing program, I'd suggest giving that a shot.  You still need to choose and position your lights carefully, but you have a lot of flexibility in adjusting levels in Ps or The Gimp or whatever.

mark128

I always render scenes with several lights.  Even when doing portraits I usually have a 3 light setup.  I adjust the intensity/location of the lights to give the effect I want.  Usually a main light, a fill light at lower intensity and then a back light on the hair.  Sometimes there are background lights to light a larger scene which are adjusted to give a pleasing results. 

If you only have one light in your scene, you can do all your adjustment in the tone mapping, but as you learn to use more than one light, you will need to learn how to adjust the different kinds of lights.