Author Topic: Lightmeters and corona  (Read 10714 times)

2016-10-19, 15:49:41

Jpjapers

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Is there any way of measuring lux levels in corona like you can with the lightmeter in MR?

2016-10-19, 18:37:07
Reply #1

Dionysios.TS

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Nice question, they asked me something similar here in studio but I don't want to go back to MR for this but probably I will... -.-

Thanks,

Dionysios -

2016-10-19, 19:49:12
Reply #2

Jpjapers

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I have a 50k square foot building and a lighting plan set up. I have the cad plan with all of the metered lux levels marked every 8-10m on the plan. Im using corona so we can experiment with light levels and temperatures virtually with lightmix. But to ensure accuracy i want to make sure that A. The lux levels match as ive read a little on here that suggests ies data isnt all that accurate. And B. So i dont have to play with lightmix then set up a separate photometric scene to measure the Lux.

2016-10-19, 20:28:49
Reply #3

Dionysios.TS

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I have a 50k square foot building and a lighting plan set up. I have the cad plan with all of the metered lux levels marked every 8-10m on the plan. Im using corona so we can experiment with light levels and temperatures virtually with lightmix. But to ensure accuracy i want to make sure that A. The lux levels match as ive read a little on here that suggests ies data isnt all that accurate. And B. So i dont have to play with lightmix then set up a separate photometric scene to measure the Lux.

The only issue you may have is the IES problem I mentioned in a previous post. And is very important if you want to have an accurate simulation.

2016-10-19, 23:04:32
Reply #4

Jpjapers

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Did you figure out a workaround? Or any consistent maths behind the problem to get it to how it should be?

2016-10-20, 11:31:55
Reply #5

Dionysios.TS

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Did you figure out a workaround? Or any consistent maths behind the problem to get it to how it should be?

Unfortunately not, I expect some news from the de team which I still never received.

2016-10-20, 13:27:59
Reply #6

maru

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Hi, this was already asked a few times, and unfortunately it seems that there is no reliable "light metering" in Corona yet. There is one thing, which might be helpful for you, depending on what exactly you are working on. Here it is...


Quote
-currently Corona does not offer any kind of automated way to measure light intensity at given point (like Vray light meter)
-it should be possible to measure light intensity in real life (I think it would be best to put the light meter as close to the light source as possible, although in theory this should not matter) and simply paste this value into Corona light, but the hardest part will be to keep realistic scale of the light emitting object, I think this will require some experimenting anyway

-here is an idea to read "real world" light intensity from rendered image:
1) set up scene in correct units and scale
2) set up light sources with correct size, units, and intesity
3) optionally, for best fidelity, use PT+PT and set MSI to really high value (more than 100, higher = closer to reality)
4) disable any tone mapping, (even set gamma to 1.0!)
5) render
6) read data from VFB. Interpret the numbers as "Watts per meter squared per steradian reflected into camera" - "original RGB" 1,1,1 should mean 1 W/(sr.m^2)

Maybe this process could be somehow reversed, but I think it will still be guessing.


Other than that, some more facts/ideas:

Quote
Corona lights support the following units:
-W/(sr.m^2)
-Candela
-Lumen
-Lux

Quote
You can paste the value which you obtain in W/(sr.m^2) from image pixel (or from your lightmeter in real life) into Corona light intensity and then change light units to Lux. But from what I understand this still requires some guessing and is more of a "workaround" than real light metering. Unfortunately it looks like a proper implementation of light metering tools will be required for this to work.

Another idea is to use native 3ds Max photometric lights as Corona supports them. You can then switch to Mental Ray and use pseudo-color exposure controls or other tools which are built into 3ds Max to get the desired light intensity, and switch back to Corona again.

Quote
it seems that the easiest way to recreate real light in Corona (or any other renderer probably) would be to find what is the light's intensity in lumen (it should be on the box/package if this is some regular light bulb, or there should be some manual with such info if this is some more advanced/photographic light). If you know value in lumen, then you should be able to simply paste that value into Corona light. If you know the power of light in W, and you know the light's efficiency, then you should also be able to convert this into lumen. Here is an example calculator: http://www.rapidtables.com/calc/light/watt-to-lumen-calculator.htm

There are also some obstacles like light color, or light shape, so it looks like this is always some simplification.

Quote
If you are not after scientific precision, I would suggest you taking a number of reference photos so that you would know the camera exposure values (shutter speed, iso, f number, etc), then recreating these exposure values in Corona and tweaking light source intensity so that the image is visually similar to the reference photos. Unfortunately I don't think there are currently any easy ways of doing this.
Marcin Miodek | chaos-corona.com
3D Support Team Lead - Corona | contact us

2016-10-20, 13:43:44
Reply #7

Dionysios.TS

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Hi, this was already asked a few times, and unfortunately it seems that there is no reliable "light metering" in Corona yet. There is one thing, which might be helpful for you, depending on what exactly you are working on. Here it is...


Quote
-currently Corona does not offer any kind of automated way to measure light intensity at given point (like Vray light meter)
-it should be possible to measure light intensity in real life (I think it would be best to put the light meter as close to the light source as possible, although in theory this should not matter) and simply paste this value into Corona light, but the hardest part will be to keep realistic scale of the light emitting object, I think this will require some experimenting anyway

-here is an idea to read "real world" light intensity from rendered image:
1) set up scene in correct units and scale
2) set up light sources with correct size, units, and intesity
3) optionally, for best fidelity, use PT+PT and set MSI to really high value (more than 100, higher = closer to reality)
4) disable any tone mapping, (even set gamma to 1.0!)
5) render
6) read data from VFB. Interpret the numbers as "Watts per meter squared per steradian reflected into camera" - "original RGB" 1,1,1 should mean 1 W/(sr.m^2)

Maybe this process could be somehow reversed, but I think it will still be guessing.


Other than that, some more facts/ideas:

Quote
Corona lights support the following units:
-W/(sr.m^2)
-Candela
-Lumen
-Lux

Quote
You can paste the value which you obtain in W/(sr.m^2) from image pixel (or from your lightmeter in real life) into Corona light intensity and then change light units to Lux. But from what I understand this still requires some guessing and is more of a "workaround" than real light metering. Unfortunately it looks like a proper implementation of light metering tools will be required for this to work.

Another idea is to use native 3ds Max photometric lights as Corona supports them. You can then switch to Mental Ray and use pseudo-color exposure controls or other tools which are built into 3ds Max to get the desired light intensity, and switch back to Corona again.

Quote
it seems that the easiest way to recreate real light in Corona (or any other renderer probably) would be to find what is the light's intensity in lumen (it should be on the box/package if this is some regular light bulb, or there should be some manual with such info if this is some more advanced/photographic light). If you know value in lumen, then you should be able to simply paste that value into Corona light. If you know the power of light in W, and you know the light's efficiency, then you should also be able to convert this into lumen. Here is an example calculator: http://www.rapidtables.com/calc/light/watt-to-lumen-calculator.htm

There are also some obstacles like light color, or light shape, so it looks like this is always some simplification.

Quote
If you are not after scientific precision, I would suggest you taking a number of reference photos so that you would know the camera exposure values (shutter speed, iso, f number, etc), then recreating these exposure values in Corona and tweaking light source intensity so that the image is visually similar to the reference photos. Unfortunately I don't think there are currently any easy ways of doing this.

Maru, at this point, the problem I found by using IES files in Corona how can be solved? Lumen, cd or lux values are not working in the same way as they do in 3ds Max photometric lights which they seem physically correct.

Thanks,

Dionysios -

2016-10-20, 13:57:04
Reply #8

maru

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I do not know the answer right now. We will definitely look into this.
Marcin Miodek | chaos-corona.com
3D Support Team Lead - Corona | contact us

2017-12-12, 16:33:42
Reply #9

Jpjapers

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I started this thread a few years back, I was just wondering if there has been any investigation into using 3dsmax lightmeters?
Considering the architectural nature of the majority of users here it seems like it may be useful for those who are working in the industry.
If anyone has a more reliable workaround than the above to measure Lux in corona scenes it would be greatly appreciated!

Otherwise, i have to resort to relux and that software is horrid.

Thanks
Jack

2017-12-13, 12:43:00
Reply #10

maru

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Sorry, but no improvements here yet, and no specific plans for the nearest future.
Marcin Miodek | chaos-corona.com
3D Support Team Lead - Corona | contact us

2017-12-13, 14:53:09
Reply #11

Jpjapers

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Sorry, but no improvements here yet, and no specific plans for the nearest future.

No problem. Relux will have to do

2019-02-07, 18:37:11
Reply #12

CarlaTuck

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Hi... I'm looking for some tips on how you could check the light level in a room.  I'm not looking for rocket science and I'm not looking for super accuracy.  I thought you might be able to do it by taking a snap shot with the camera and somehow checking the average color... or something like that. Also, want to know about your setup. do you have your components embedded on PCB and could you pleas show me PCB Assembly and its design? How are you managing the heat of components?
« Last Edit: 2021-12-09, 13:26:45 by CarlaTuck »

2019-02-08, 08:45:13
Reply #13

Tanakov

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I did have this challenge lately and I simply eyeballed all the lights, because all the methods were as good as that.

There are specific programs for light simulation and I would recommend you use it or contact a dealer and ask them to do that for you (they usually are helpful)
Using Corona since 2014-01-02
https://www.behance.net/Gringott

2019-02-08, 09:55:09
Reply #14

sprayer

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Hi... I'm looking for some tips on how you could check the light level in a room.  I'm not looking for rocket science and I'm not looking for super accuracy.  I thought you might be able to do it by taking a snap shot with the camera and somehow checking the average color... or something like that.
https://knowledge.autodesk.com/support/3ds-max/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/3DSMax/files/GUID-0BD33141-AA1C-4FC1-AD33-3F011B4721FA-htm.html
https://knowledge.autodesk.com/support/3ds-max/getting-started/caas/CloudHelp/cloudhelp/2015/ENU/3DSMax-Tutorial/files/GUID-65DD9716-74C7-405F-B05B-9E8C1E2CA306-htm.html

maybe this helps. for corona there is no tools