Emissivity, over-exposed? Help :p

Robinson

So I wanted some light in my hallway.  I imported a light mesh obj and then set one of the materials (the "bulb") to emissive.  The emissive settings are as follows:

 

Emission Temperature: 6000
Emission Profile: None
Emission Colour (RGB): 1.00    1.00     1.00

Luminance: 2500.00 (kcd/m^2)

 

My problem is I don't think it looks quite right.  The falloff seems wrong, i.e. very, very bright right near the bulb and then kind-of dim bounces off the walls.  Should I choose an emission profile for this and if so, which one?  Other than that is there a way to change the falloff so it's more even and brighter at a distance?  The bulb looks over-exposed to me.   I had to ramp up the luminance in order to get a reasonable amount of light on the walls but it seems way too high.

Here's a picture showing what the model and scene look like:

 

nonesuch00

Problem is

a) in Europe & the Western Hemisphere indoor light is almost always about 3500K not 6000K.

b) Those very high kcd/m2 aren't really good except if you CPU render & use those high values as a cheat to reduce render times. If you have a fast & iRay capable nVidia video card you do yourself a lot of 'artistic good' by using 5000 or 10,000 iterations/samples but more realistic lighting values. If you don't know what those should be in candelas or lumens than use watts. The scene will look too dark at first but as it gets closer to 5000 or 10000 or whatever it will start looking realistic. 

c) If it's still too dark then introduce low level evenly distributed ambient lighting throughout the whole room be using an invisible DAZ primitive plane just below the ceiling and setting it up to emit about 200 watts, probably less, more like 60 W - 100W. As the light bounce calculations add up you should get a brighter and brighter room as the render nears its finish. If you have too much fake light and let the render run all the way to the finish you get too much light added to the scene via bounces (bounces equals ambient light) and it gets too bright (that's why I said those adding bright light sources to speed up renders only works if you render 2000 iterations or less on a CPU and similar GPU situation).  So unless you are trying to artificially complete a render with less than 2000 iterations adding extra bright light sources isn't a good ideal artistically. You could in the Tone Mapping setting adjust exposure instead to create artificial brightness.

Sevrin

That kind of light is typically used as much as accent pieces as for illumination, so if you rely on them as the sole source of light, you'll have to dial them up pretty high. 

You might want to try turning them down and then placing ghost lights on the wall sort of where their mounting plates would be in order to get approximately the same amount of illumination, but without blowing as much of the lamp details.  Also, if they're supposed be incandescent, you might want turn down the temperature a bit more, but that's just a suggestion.

Robinson

This is reduced temperature (3.5k) and switched out to 30W, and with 3,000 iterations.  I also fiddled with the tone map settings.  Unfortunately the tone map change over-exposes what you can see in the lounge to the left.  I suppose I can justify this as the eyes adjusting as you move from one lighting environment to another.  I think it's unlikely I'm going to win this battle with physics... 

 

maclean

To get the effect you want, you'd be better to create your own IES profile for the lamps.

https://www.vertheim.com/ies-generator.html

It's easy enough to do (Stand-alone software - No install). Just drag the graph line, look at the preview, then save it and load it into the IES profile channel in DS.

Robinson

So the problem was the tone mapping.  I'd left it as default and that's really for outside, cloudy day.  I reduced exposure to 6 and then damped all the lights in the scene right down.  This is more or less what I want in the hallway.  The lounge render now looks OK too.

Getting tone mapping right is sooo important.

With respect to emission profiles, they really don't like certain types of surface geometry, i.e. they probably only work on planar surfaces, not some generic mesh.  Anyway this is more or less what I wanted:

Sevrin

Emission profiles work with whatever, but the direction of the light is less predictable with emissives than it is with spotlights.  When improvising emissive lights like you did, they will as often as not point in some other direction than the one you prefer.  They're ideal for dramatically illuminating architecture with directional lights once you get them figured out, though.

mwasielewski1990

Robinson said:

So the problem was the tone mapping.  I'd left it as default and that's really for outside, cloudy day.  I reduced exposure to 6 and then damped all the lights in the scene right down.  This is more or less what I want in the hallway.  The lounge render now looks OK too.

Getting tone mapping right is sooo important.

With respect to emission profiles, they really don't like certain types of surface geometry, i.e. they probably only work on planar surfaces, not some generic mesh.  Anyway this is more or less what I wanted:

As someone before said: Higher ISO, lower emission on the small bulbs, and place an invisible mesh light in the center of the room. So:

1) Set iso to anywhere between 150 to 200 (50-100 is good for outdoor scenes with a lot of light)

2) Emission on the bulbs maybye 900-1000kcd/m

3) Go to Create -> New Primitive -> Sphere -> Diameter depends on the size of the room, but by eye maybye 1m should be enough? Or maybye a bit smaller, or bigger, just use the Scale dial in Parameters tab. Place the sphere in the middle of the room

4) Click the Surface Selector tool, select the sphere

5) In the surfaces pane of the sphere go to Emission property, and try anywhere between 300 to 600kcd/m

6) Then go to Geometry property -> Cutout opacity and set it to 0 (zero)

You should get the desired result. I hope that was helpful.