Difference between HDR and SpotLight / Mesh light
Hello everyone,
I've been working with DAZ for a few months now and have gotten quite good at it, but there is something that I still struggle with, and that is the differnt forms of lighting.
Working on my last outdoor scene with an HDR lighting dome was a breeze, my character's skin looked very natural without much tweaking on my part, the scene was well lit, and it rendered to an acceptable level in just a few minutes.
The current scene I am working on takes place in a storage room, so there are no windows or other natural light sources available and I have to rely entirely on my own scene lighting. I have spent the past few days fiddling around with different options: Using ghost lights / mesh lights, a 3 point spot light setup, tweaking the tone mapping options like the ISO setting and the shutter speed, and I can generally get the scene to be lit OK, but my character's skin seems to look very "flat" for lack of a better word. Most of the skin details are missing, normal maps look like they are painted on, skin reflections look sometimes waxy, and reflections on water will often leave black spots. Render times have increased massively, and it takes at least 30min for all the noise in the image to disapear, making it rather difficult and time consuming to iterate on different settings.
I guess my main question is: Can someone explain to me what the main difference between an HDR dome and the various other options like mesh or spot lights are in terms of the light they emit, if any? Why am I seeing such a stark difference in results and is there any way I can replicate the "depth" of the HDR light indoors without using section planes or hiding the room's ceiling? Or am I just not finding the right combination of settings for my current scene?
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HDRs produce light from all around, its intensity determined by the colour of the HDR in that direction. Local lights produce light only from the light itself, though Point and Spot lights may be given a shape to increase the source area; other areas are lit only by light bouncing off surfaces. Without an image it's hard to guess what your issues are - too large a light source washes out fine detail; too small, and you are increasing your reliance on light bounces which will greatly slow the convergence of the image down (it will take a long time to lose its noisiness).
Hello Richard,
thank you for your reply.
So if I understand correctly the main difference is that the HDR is a sphere that projects light towards its center and may have different color values across the surface, as opposed to something like a spotlight that will only emit a single color from its surface in a specific direction? So I assume it won't be possible to replicate the effect of an HDR without a sphere that has a lighting map of the room?
Ok, so far I have been relying on a ghost light that stretches over most of the ceiling of the room to generate some base lighting and additional spotlights for shadows and atmosphere. Would you say that might be the reason for the effect I'm seeing? Do you happen to have any tips on how large the surface of the mesh light should be in relation to the room or is there another technique I could try? Maybe have different, smaller mesh lights from different angles?
Thank you for taking time out of your day!
A couple of things to look at.
1) Make the ceiling Emissive and use the ceiling diffuse map in the Emissive colour map.
or/and
2) If there are any light fittings make the bulbs Emissive.
3) Use a Linear Point or Point light as the main light and then use a few more for fill light.
or (Least believable in my opinion)
4) Hide the ceiling and use a HDRI.
I have taken the file referenced in Ceiling -> Diffuse -> Base Color and set as the emission color under the emission tab with the color set to white. Is that what you meant? The diffuse map for the ceiling is the same texture used as the base color, it is just a slab of concrete.
I'm able to light the scene this way, but the ceiling is noticably brighter than the walls, which won't really work for me, unless I misunderstood your initial suggestion.
The room only has a single light source, but I tried placing a couple more and it did indeed increase the lighting quality. It's nowhere near the HDR, but definitly an improvement, so I'll play around with that setup a bit more.
I will give that a shot, I haven't really worked with linear point lights as of yet and always wanted to try them out. Just for my understanding: Wouldn't point lights lead to relatively sharp edges on shadows, much like a spotlight with the geometry set to point? I have mostly resorted to using spotlights with the geometry set to circle and both width and height set to around 25-50, although I have a feeling this might negatively affect the color depth of whatever is on the other side of that spotlight as well.
Thank you very much for the input!
With the ceiling lower the Lumen, I have had it as low as 0.1 to get the light I wanted :)
You wont get the same light inside a room like you do outside with a HDRI. Think about your own room and the way the light acts. Some areas will be bright, some darker and other places in shadow.
This image uses the Emissive ceiling and the desk lamp at top left the bulb is Emissive shining down on the desk.
Note that in Iray a Linear Point Light is just a Point Light - Iray doesn't do non-physical falloffs.
If it's an enclosed scene, a mesh light made out of some kind of sphere is probably going to give you the most realistic lighting since in Iray, since it will bounce and light the entire room. I'm not a fan of photometric point lights because as the name implies, the light emanates from a single point. This tends to result in overly harsh and unrealistic shadows. A mesh light sized to the realistic size of a bulb (or a cylinder if you want florescent tube lighting) will provide better results.
However (it's been awhile since I've done this in Studio, but this is just general lighting advice), a simple primitive sphere often won't give very good results. This is because the primitive sphere doesn't actually have any geometry to work with. Ideally, you want a polygon modeled sphere.
As Fishtales suggested, you can also make existing light fixtures emissive. But this often doesn't provide very good results because you might end with weird self-shadowing and strange shadow artifacts.