IES strange intensity behavior

[Dionysios.TS]

Hi all, I am working on a big international project and I am having some issues by using IES file information in Corona. I really need an accurate simulation but I have some strong doubts on how the engine treats the IES files and their intensity values.

In the past years I always used the native 3ds Max photometric lights where once loaded an IES file, the intensity values are driven automatically so the "cd" and "lm" values are written as in the file by the manufacturer.

In Corona of course this doesn't happen, so the user must manually do this and here is where I find a big difference or BUG?!?!?

Take a look at the IES Comparison image I uploaded here, the 3ds Max Photometric Light reads automatically and correctly the "lm" value. Now if we want to get the same result in Corona the "lm" value has to be set too way low?!? How this is possible? This kind of difference is very important for a natural based result!

The IES file has a 2.217,831lm value and Corona must be set to 47,123lm for the same intensity result!
Also in the 3ds Max Photometric Light's menu, if you change from "lm" to "cd" the values are correct but in Corona, if you change from "lm" to "cd" and you put manually the values from the IES data information, the result is different! O.o

I included a iGuzzini IES file here and from the IES info I read:

5.129.6cd which are 2.291,772lm

In Corona, 5.129.6cd has different intensity results if compared to 2.291,772lm. What a mess... :(

Looking forward for an answer.

Thanks,

Dionysios -


 

[Juraj]

'Might' be because in CoronaLight, IES is still area light, which is super-odd, like, what kind of size do you create analytical point light :- ) ?

[Dionysios.TS]

I just need to simulate the correct lighting effect in the space. The architects here need to see a "realistic" output and not my artistic point of view and is very understandable.

If I use also a Corona Sun element in the scene and my IES files are so wrong with their values, well, the result is NOT ok and everything becomes messy.

[pokoy]

I don't know if this is a coincidence but Corona's 47,1 squared (47,1^2=2218) is very close to the 'real' value displayed the photometric light. Maybe test it with other values and if it's roughly the formula you have a rough estimate at least.

[Dionysios.TS]

I don't know if this is a coincidence but Corona's 47,1 squared (47,1^2=2218) is very close to the 'real' value displayed the photometric light. Maybe test it with other values and if it's roughly the formula you have a rough estimate at least.

Didn't noticed that... I am curious to know what the dev team thinks about.

Thanks guys for your answers.

Dionysios -

[pokoy]

It's not exactly the square so it really could be by coincidence, best would be to verify with different IES files.

[Dionysios.TS]

Already tried and they work all the same way unfortunately.

[Dionysios.TS]

Any news from dev team here?

Sorry for stressing you guys but I would like to know if you know anything about these issues.

Thanks,

Dionysios -

[mferster]

'Might' be because in CoronaLight, IES is still area light, which is super-odd, like, what kind of size do you create analytical point light :- ) ?

Maybe I'm missing something... but I thought it only became an area light when you uncheck 'keep sharp patterns? Otherwise it stays a point  light regardless of the size of the shape, is that not the case?

[Juraj]

'Might' be because in CoronaLight, IES is still area light, which is super-odd, like, what kind of size do you create analytical point light :- ) ?

Maybe I'm missing something... but I thought it only became an area light when you uncheck 'keep sharp patterns? Otherwise it stays a point  light regardless of the size of the shape, is that not the case?

Now that you mention it, that might be the case ? I honestly didn't know. So if I check ON "keep sharp patterns" (it's stupid name then no?), the size of the light doesn't matter ? If yes that's wonderful, and I've been misled.

[mferster]

Yah, here are the differences between 2 long rectangle ies area lights with 'keep sharp patterns on' the left, and right with it off.

*EDIT

..... but as for the topic at hand. Corona and the 3ds max do treat the conversion from candelas to lumens differently.

in corona 1 cd = 3.142 lumens

in 3ds max photometric 1cd = 12.566 lumens

I also pulled this from the lumens wikipedia page

The lumen is defined in relation to the candela as

    1 lm = 1 cd⋅sr.

A full sphere has a solid angle of 4π steradians,[1] so a light source that uniformly radiates one candela in all directions has a total luminous flux of 1 cd × 4π sr = 4π cd⋅sr ≈ 12.57 lumens.[2]

so something is happening differently between the two. Hopefully Ondra can illuminate what's going on ;P.

[Jpjapers]

Glad i read this. i was about to go into work tomorrow and light a 50k sqft building with ies lights and play around with lightmixer. maybe ill postpone that project until one of the team chimes in :D

[Dionysios.TS]

Yah, here are the differences between 2 long rectangle ies area lights with 'keep sharp patterns on' the left, and right with it off.

*EDIT

..... but as for the topic at hand. Corona and the 3ds max do treat the conversion from candelas to lumens differently.

in corona 1 cd = 3.142 lumens

in 3ds max photometric 1cd = 12.566 lumens


I also pulled this from the lumens wikipedia page

The lumen is defined in relation to the candela as

    1 lm = 1 cd⋅sr.

A full sphere has a solid angle of 4π steradians,[1] so a light source that uniformly radiates one candela in all directions has a total luminous flux of 1 cd × 4π sr = 4π cd⋅sr ≈ 12.57 lumens.[2]

so something is happening differently between the two. Hopefully Ondra can illuminate what's going on ;P.

Exactly, this is the point and I think is a mess.

Can you guys try to check if your IES files have the same differences? Would be nice.

Thanks in advance,

Dionysios -

[mferster]

yep It's not exclusive to ies lights though, corona lights and photometric lights behave differently at different lumens.

But here is the thing... I think the corona light intensity is actually correct using lumen values.

I think the issue is that corona interprets photometric lights incorrectly based on some quick tests I did using photographic exposures, but I could be wrong and overlooked something.

[Dionysios.TS]

Didn't received any news from the dev team IES problem and neither another post about Kelvin colour problems (https://forum.corona-renderer.com/index.php/topic,13377.15.html)...

I guess guys you're busy these days but would be nice to know if there is something wrong with both issues or not.

Thanks!

Dionysios -