Emitter not lit up

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Bosseye
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Emitter not lit up

Post by Bosseye » Fri May 05, 2017 9:35 pm

Odd one - using an IES profile for my lights, works fine when the lights are a certain size. But when I make the area of the emitter larger it stops lighting up. So for example it all works find with a 50mm spotlight, but if I make it a 200mm spotlight suddenly the source doesn't light up/glow.

Whats odd is that the light still functions and the fall off still casts on the walls correctly - its just the actual emitting 'bulb' is no longer is lit up.

It doesn't clear up the longer it renders either.

See below. Literally all I've changed is the size of the emitter. IES is the same, block is the same, emitter material is the same etc.

Working fine, 50mm spot
Capture2.JPG
Not working, 200mm spot
Capture.JPG
At the moment I'm having to add white in postpro.

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galinette
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Re: Emitter not lit up

Post by galinette » Fri May 05, 2017 11:51 pm

The IES profile sets the total amount of light emitted by the object in lumen.

If you scale the source by 4x, its area is multiplied by 16. The lumen value being constant, it has to emit 16x less light per area unit. Which means the source surface appears 16x less bright. Since it looks like you have daylight, the source brightness becomes lower than the surrounding daylit ceyling.

There is nothing you can do about this. If you want to increase an area light source size, you have to either:
- Increase its total luminous flux
- Decrease its apparent brightness

But you can't keep both constant.
Eclat-Digital Research
http://www.eclat-digital.com

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Bosseye
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Re: Emitter not lit up

Post by Bosseye » Sat May 06, 2017 1:18 am

Ok, thats interesting, thanks. I'm still confused though!

How does one go about changing luminous flux etc?

The only emitter options in SKIndigo appears to be emission scale - increasing this doesn't resolve the issue.
4.JPG
See below, small spot light (50mm diameter), then one increased by 4x and then the last increased by 4x again.

Obviously the emitter isn't white like it should be, and the fall off pattern on the wall is looking all wrong too. Why does that change? It looks zoomed in. Is the fall off pattern affected by the size of the light?

I've not noticed this issue before.
1.jpg
2.jpg
3.jpg

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Oscar J
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Re: Emitter not lit up

Post by Oscar J » Sat May 06, 2017 1:29 am

The spotlight *shouldn't* necessarily be white, depending on from where you're looking at it. If you're viewing the spotlight from a position outside of its light "cone", you will receive no or very little light from it.

IES lights should preferably be kept small. If I recall correctly, each triangle in an IES spot will emit light with the defined profile. If you have a large circle consisting of multiple triangles far apart from each other, each emitting the with the IES profile, it will result in a much more blurry looking fall off pattern.

Eneen
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Re: Emitter not lit up

Post by Eneen » Sat May 06, 2017 1:44 am

That "IES from triangle" is really unique and powerful in Indigo. That way when you assign IES to very long rectangle divided into small squares you will get pretty accurate LED stripe :)

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Bosseye
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Re: Emitter not lit up

Post by Bosseye » Sat May 06, 2017 1:56 am

Ah, ok.

Funny how I've never noticed this before, every day is a school day!

Obviously my qiuick and dirty emitters aren't viable for this project (for speed I did a simple face with the emitting texture applied) What I've done then is make a spotlight in a marginally more realistic fashion - I've got the wide 250mm spotlight casing, and I've got 1 small 50mm diameter emitter recessed within it and a translucent lampshade material over the face.

Its showing up as I want it now, and as a side effect, the falloff pattern isn't quite as aggressive as I had it previously, presumably as its filtered through the shade material - so the light is washing about better, makes the walls look less contrasty.

Thanks for your help both.

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galinette
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Re: Emitter not lit up

Post by galinette » Sun May 07, 2017 8:31 pm

Bosseye wrote:Ok, thats interesting, thanks. I'm still confused though!

How does one go about changing luminous flux etc?

The only emitter options in SKIndigo appears to be emission scale - increasing this doesn't resolve the issue.
Glare should definitely add a way to scale the IES emission. It seems it only works without IES enabled.

Etienne
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