The Spotlights Don't Work in Iray
megagearx_eaad3c70d6
Posts: 60
in New Users
The picture is grainy, but that's not the problem. I just stop rendering as soon as I see that something is missing!
I want to have a spotlight lighting up the building in the background and a glow in front of the children. But nothing WORKS!!!
Spotlights, Linear Pointlights, Pointlights...nothing works with Iray.
I have Dome and Scene selected in the Environment tab. Infinite Sphere with Ground is selected. Draw Dome is on.
What am I forgetting here?
Proof.jpg
1509 x 901 - 2M
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If the dome is lighting the sceen you will need a very strong spotlight to have a visible effect - just as you'd need a strong light to show on a bright day out doors.
I increased all of the lights to 1000%. No change.
Don't, for Iray, adjust by intensity - with Photometric On (the default) adjust the Luminance value instead.
I find that luminance values need to be in the millions to be visible. My exposure value is also around 20 meaning I need much more light. It seems to give me better and faster renders.
Switch to Scene Only to set the balance for any scene lights, such as spotlights. Otherwise it's too difficult to know which lights are contributing. Once you get the individual lights working, switch back to Dome and Scene. It'll likely now be overlit if you cranked up the spotlight values, but you can change the environment intensity to compensate. Good lighting is a matter of balance.
Using this page https://en.wikipedia.org/wiki/Orders_of_magnitude_(luminous_flux) very handy page to save or take screen shot of and put with your light source files
the Sun lumins is roughly 3.6 x 10 to the 28th power OR 3.6 x 10,000,000,000,000,000,000,000,000,000,0 OR 3.6 x ten octillion,
the reason is distance and area covered between target (earth) and light source (sun)
So for your image you must take into account the area you want to cover with the spot light (spread angle) and how far away will your spot light is from your target (Beam Exponent)
EDIT: here is a good article about Beam Exponent or beam Distance in relation of Lumins
https://maglite.com/maglab/ansi_lumen_vs_beam_distance__peak_beam/#.WT5HVrszWHs
I don't see how the sun compares to spotlights, which at best are poor collimators or light. At the earth's surface the sun's rays are nearly parallel; because of this, and considering lighting things just on earth, those rays don't exhibit divergence or falloff (except through a lens), and the 93 million miles distance means there's no perceptible inverse square law to consider. Both falloff and inverse square are important to working with point or spotlights. Seems like bringing up the sun in reference to spotlights is a red herring to the discussion?
The D|S distant light is engineered to be similar to the sun, with collimated parallel rays from an "infinitely small" source. There is no falloff or inverse square -- the distance between the light and scene is intentionally ambigous, and doesn't factor in. The lumens control adjusts light incident on the scene, and not lumens from the source.
And what does smoked fish have to do with Luminance values in Iray and why they (the lights) have to be in the millions to be visable ?
I don't remember ever having a light set in the millions to have it seen in Iray.
My spotlights are in the 10s of thousands and they're pretty bright. The confusion comes from the units of measure for measuring lumens. Iray's base unit is the square meter; D|S base unit is the square centimeter. The only light source in D|S that lets you set the units is for geometry emissive shaders. It's a good way to see why there is this apparent disparity. Try setting it to lumens cm^2 and then lumens m^2. When set to cm^2 a value of 500 is so bright it might burn out a character standing close by. Set to m^2 there's hardly any illumination at all.
It can also be seen in the differences between 4.8 and 4.9. In 4.8, distant lights under Iray were set to incident light per cm^2, so a value of 10 approximately reproduced noonday sun. In 4.9, for whatever reason they changed to light incident m^2, requiring you to multiply the old value by 10000 to achieve the same result. It's the same light, but now calculated at a different unit of measure.
I have to suggest this, I've thought about it quite often. I think there should be a "create new 3Dlight spotlight" and "create new IRAY spotlight" selections in the menu. Newcomers plop in a spotlight and have no choice but to come here and search, ask and fret about why it shines no light and those of us who do use the software have to go fiddle with sliders when it would be so nice to just plop out a spotlight for Iray and have it work as expected. You could make the default settings the easiest for each renderer and if it needs fine tuning then we can always go fiddle with sliders but it would be nice to have it just ready to go.
That was how the initial versions of 4.8 went - and people then wanted them unified. As long as you don't have Show Hidden Parameters enabled in the pane's option menu then the available parameters should make sense.
Well that's just it: who's expectations? Mine are likely different from yours. If you mean some default setting appropriate for Iray or 3DL, that's sorta-kinda what it does, though the value for Iray is quite low. I suspect Daz things you'll just make a preset of the lights you use most, but most new users have no idea what presets are, where to find, or what to do with them once they find them.
I suspect this is the best they can do without providing a beginner light set as part of the default materials download.
There's nothing horribly wrong using a non-photometric light with Iray, but doing so will make the light output ratiometric instead of photometric, the difference being that the intensity of photometric light follows the human vision curve, rather than being a simple linear line.
I'm talking about the expectation of adding a spotlight and having it actually illuminate the subject. As it stands, in Iray, the default settings of the spotlight throws no visible light at all. As I said above, you can fine tune it for your subject but a good starting point for any light would be that it light things up.
Here is a quick render of a cube (with a plane floor) illuminated by a single spotlight; it actually illuminates the subject. The render settings and spotlight settings are the default, except for 'Scene Only' in the environment settings. One thing to note is that the default tonemapping settings are for a sunny day; the default spotlight is not as bright as that. More importantly, unlike 3delight, the builtin spotlight behaves like a real-world illumination source, and the light flux falls off in an inverse-square relationship. The spotlight in this image was place pretty close to the cube; move it twice as far away, and the light is only a quarter as bright (well, it falls on an area four times bigger, and so each bit of that area gets only a quarter as much light). So it would be impossible to have a default spotlight that is 'right' for a particular image, since placement will change the required intensity, pretty much as it does in a real photo studio.
For an outdoor scene, you need a very bright spot indeed to compete with sunlight, as others have pointed out.
Late to the party, but commenting because this is where I ended up when searching for answers.
As said above, it's fairly simple if you know how to do it. It only took me two weeks to put all the pieces together, despite searching!
There is a handy tutorial here. All it fails to say is that you need the iray environment set to Dome and Scene. https://www.versluis.com/2017/04/how-to-use-spotlights-with-nvidia-iray-in-daz-studio/