IES strange intensity behavior

[Juraj]

I have attached a test I made a while ago.
On the left there is a real world reference (2 cheap light sources).
On the right a simulated environment with 2 Corona Light that have correct light intensity and position in space relative to the subject.
The settings and exposure of the virtual camera also match the real camera.

Karnak, this test is done with IES light profile ? (And if so, IES left as area light or as point light (keep sharp patterns).

[karnak]

Hi. The test was done with IES "Keep sharp patterns" on.
The IES file was not of the same lamp, I searched for a similar one, but lumens output was correct.
It is not an accurate test by all means. What are your thoughts?

[Juraj]

Great :- ) Just wanted to know when the IES is accurate (keep sharp patterns or not). This gave me the answer :- )

[Jpjapers]

Im confused. So is there a way in max using corona of getting accurate IES Intensity or not?

[mferster]

So here are the problems:

1. When you load an ies file in a corona light, it doesn't automatically use the manufacturers lumen value that's stored in the file.
   (using a 3ds photometric light, loads the correct lumen value)

2. Corona lights and photometric lights are inconsistent from each other when they share the same dimensions and lumen value.
(corona lights are significantly brighter in this case.) The confusion is arising from not knowing which light is physically accurate.

3. When switching from candela units to lumens they produce inconsistent conversion values.
(Corona lights don't take into account the shape of the light when converting from candelas to lumens.)

a fully exposed sphere of light should be 1 cd = 12.566 lumens  (as it is in 3ds photometric lights)

all corona lights regardless of the shape of the light (from dropdown menu or light distribution data from ies files) convert 1cd = 3.142 lumens

[Jpjapers]

So if i use photometric lights in corona i can get a somewhat accurate simulation still?

[mferster]

No, I don't think so.  I could be wrong but based on some quick tests I've done, I think corona is interpreting the lumen/candela  values from 3ds max photometric lights incorrectly because while 3ds max takes the shape of the light into account, corona does not.

If you want the most accurate light for a pot light as of this moment this is probably the most accurate; load up your ies files in a corona light, make sure it's on disc or rectangle, make sure keep sharp patterns is turned on, look up the lumen values from the light manufacturers spec sheets and put that in the lumen value of your lights. That should be the most accurate.

If you have free floating hanging lights, it's a bit more obtuse.

[Juraj]

No, I don't think so.  I could be wrong but based on some quick tests I've done, I think corona is interpreting the lumen/candela  values from 3ds max photometric lights incorrectly because while 3ds max takes the shape of the light into account, corona does not.

If you want the most accurate light for a pot light as of this moment this is probably the most accurate; load up your ies files in a corona light, make sure it's on disc or rectangle, make sure keep sharp patterns is turned on, look up the lumen values from the light manufacturers spec sheets and put that in the lumen value of your lights. That should be the most accurate.

If you have free floating hanging lights, it's a bit more obtuse.

Is the shape and size of the light in this 'particular' case then truly irrelevant as it should ?

[mferster]

Yes,  as long as your using lumens or candelas as your unit, the light shape between rectangle and disc are irrellevant, as long as it's not sphere or cylinder.

Based on the 1cd = 3.14 lumens that's present in corona's unit conversion. this equals to an 120 degree apex angle which is roughly the same as most ies files for pot lights.

If you want to see this in action load up an ies file,  switch to lumens, click on keep sharp patterns and cycle through the different shapes.
(rectangle and disc stay the same, because they are acting like a point light)

next

switch it to the default lighting units and then cycle through the shapes they will all act differently.

[Dionysios.TS]

Good morning all, excuse me for turning back on this but I am curious to know if the dev team is working on the IES mess so they can put some order on this. :)

Thanks!

Dionysios -

[Ondra]

sorry, with everything else going on, this is on pretty low priority right now

[Dionysios.TS]

sorry, with everything else going on, this is on pretty low priority right now

No worries, is important at least to know is in your To Do list... :)