Visible IES lights

[sirchris]

IES lights render invisible, often this is also what we want, but for some cases it is useful to have them visible and have the right intensity depending on viewing angle,
for example for glare analysis or for a simple approximation of the luminaire exit window without having to add an additional lights.

I tried some tricks with glossy reflections but that is not really workable.

[andy51]

As in this image, the light fitting, ceiling and wall would be modelled in a 3D program, the bulb itself would be for example a small vraylight (sphere), otherwise you would not see the actual light... the pattern on the wall, is the result of the data in the IES file, describing how the light is distributed from said light fitting. It is visible in the sense that you see the pattern, but cannot be made to show the actual light, since there is nothing apart from the distribution and luminosity (pattern on the wall) described in the IES file.

[sirchris]

Hi Andy, thanks for your answer, but this is not entirely correct. IES files contain a definition of the exit window, either a rectangle, circle, ... Iray and mental ray can render this shape,
with the correct brightness, and also lighting calculation programs like Dialux or Radiance do visualize this. Btw. Corana can do this as well.

This is a nice feature to have as the emitting surface will have the right brightness depending on viewing angle, so when you apply glare/bloom you get a strong halo if you look
directly into a spot, and much less if you look at an angle. Of course you can model this by modeling the bulb, emittor and reflector etc.. but using the data from the IES makes this
much more generic and simpler to set up.

[andy51]

https://corona-renderer.com/forum/in...topic=13397.30

From what I can find out, in the above thread, corona doesn't generate a visible shape, from an IES file, you have to create the disc or plane (rectangular) light, to which you attach the IES file. You also need to know the value of the light (IES) to get an accurate value etc etc. I may be wrong but I have never heard of Iray, MentalRay or Corona, being able to render the physical light shape from the data stored in the IES file. Perhaps you could show us how it is done, in any of those.. While Photometric lights, such as those used in Max can be made renderable and photometric lights can indeed use IES profiles, similar to the way corona does things, I am pretty sure the shape and visibility of the actual light, doesn't come from the IES file itself and has to be created by the user.

As I said, I could be wrong, I am not expert.. the only setting other than the IES files used, that I can find in Corona, is the use sharp pattern or whatever it is called. I don't know Metal Ray or IRay, however I have yet to find an example of an IES file rendering in any way other than generating the distribution / pattern of light, stored in the IES

If you can demonstrate using example images, from Mental Ray, IRay, Corona, to show them doing what you say, then by all means I would be interested to see and be corrected at the same time.

While I would love to have Vray set up a visible light source, when using IES files, to save me creating them separately, I still cannot find any mention of example of the visible light source, being rendered by any of the mentioned render engines.

[sirchris]

Here is a description of the IES format: http://lumen.iee.put.poznan.pl/kw/iesna.txt

See section 3.15:

Luminous Opening Dimensions (Identifier Line 10) While the term "luminous opening" is somewhat ambiguous for many architectural
luminaires and other light sources, it is useful in calculating average luminaire luminances and modeling the luminaires as homogeneous area light sources.

V-ray also reads this information and uses it for soft shadows and you can set it to also use it for illumination, but you cannot use it for direct visibility (what i want).

Let me show you a few examples, as i like a challenge:

Indeed corona does not read the shape and intensity from the IES file, but it uses the distribution for brightness when you define a shape.
Below two IES spot lights, on the left in each picture a 12 degree beam angle the other a 60 degree angle. When looking head on, the right picture, you can see
the 12 degree becomes much brighter as the light is mostly emitted in that direction. Both lights were set to the same intensity.



With a trick it is also possible in v-ray, but this is not preferred as it converges slowly:



Since IES lights are visible in specular reflections you can look to the scene via a mirror with a glossiness < 1.0, here i used 0.98 and turned fresnel reflection off.

This hack would not be necessary if v-ray would have an option to render the IES light areas with direct visibility.

[andy51]

Thanks for the examples and the more thorough explanation

So V-Ray would obviously need the user, as it does in Corona, to model said light shape (rectangle or circle), to make use of said data in the IES file, as Corona does.

So since Corona cannot render that data as a visible area light, as you said it "uses the distribution for brightness when you define a shape", so you should do the same with V-Ray and what you want is for V-Ray to use that data, same way as Corona does.

which is not making the shape defined in the IES file visible, but using a visible light shape (rectangle or circle), which can be made visible/renderable, and using said distribution for brightness data from the IES file, so that the light, changes in brightness, (also affecting glare and bloom) dependant on the angle it is viewed from....

So you still have to model additional lights, to get vray to render them as visible light sources, but you want those sources to use data from the IES, in order for them to render more physically accurate results, especially in the area of bloom / glare

My head is starting to hurt now.. Think I will just stick to putting in a window to my interiors and using daylight

[sirchris]

Haha

No I did not explain that, but V-ray DOES read the shape and intensity from the IES. As you can see the two ies lights in max have different shapes, i did not set this up, this was defined by the ies on import.

[Vizioen]

Very interesting.