Author Topic: [Question] - Lux unit in corona light  (Read 741 times)

2023-02-17, 13:01:21

Jpjapers

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Is the lux unit in the corona light lux at a specific distance from the source?
Usually lux measurements in lighting data is measured at a specific distance. Is this the case for corona lights and if so, what is the distance?

Thanks

2023-02-23, 13:06:00
Reply #1

Jpjapers

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I know this is a fairly technical question and likely one for devs themselves but without knowing if its lux at 1 system unit2 or lux at 1m2, and without a way in corona to actually measure light at surface level, its hard to know if youre accurate when youre trying to render lighting from measurements or datasheets.

So if any devs can confirm whether the lux is calculated using the Standard 1 lm/m2  = 1 lux at 1m distance or if its calculated with the system unit , that would be really helpful.

I recently saw Maru add a tracker ID to an old post about a surface light metering system in corona and i am very much looking forward to seeing that as a feature some day.

For anyone wondering what im talking about, this page is useful to understand the different lighting units and how theyre supposed to be used.
https://www.auersignal.com/en/technical-information/visual-signalling-equipment/luminous-intensity/
« Last Edit: 2023-03-21, 13:38:09 by Jpjapers »

2023-02-24, 10:47:31
Reply #2

maru

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Hi, I got some info on this from our almighty devs:

We are always using the standard formula for lux:
1 lx = 1 lm/m^2

3ds Max cannot be set to "generic" system units, it's always some actual unit like cm, mm, inch, etc. Thanks to this, we always know what the scale of the scene is, so that we can interpret it correctly. 

As for the conversions - Corona internally uses radiance:
radiance = lux / (683 * PI)
radiance = candela / (683 * m^2)
radiance = lumen /  (683 * PI * m^2)

The radiance unit which we are using is watts per square meter per steradian.
Marcin Miodek | chaos-corona.com
3D Support Team Lead - Corona | contact us

2023-02-24, 12:52:50
Reply #3

Jpjapers

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Awesome thanks Maru, So independent of the system/scene units the lux measurement is always the standard 1 lm/m^2 at a distance of 1m?

Because 1 lumen m^2 at a distance of 1m and 1 lumen/m^2 at a distance of say 10m is going to look quite different.

2023-03-03, 14:51:28
Reply #4

maru

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I have little knowledge on light metering, but this is backed up with Wikipedia and a quick chat with our devs:

lux is illuminance (luminous flux incident on a surface)
you can, for example, spread a flux of 1000 lumens over some area
full moon has specific lux, overcast day, office area, etc

lumen is luminous flux
it is the total quantity of emitted light

Lumens are usually used to measure "light intensity" (how much light a light source emits).
Lux is usually used to measure the amount of light on some area.
Generally, lux as a unit makes little sense as a light source intensity unit.

From Wikipedia: "The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. The same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2."
^The above is also true for a Corona Light.


Let's imagine a rectangular surface which has some width and length. This surface reflects all the light it receives. We measure illuminance over that surface and we get a lux measure of X lux.
Now, if we create a rectangle Corona Light, set its width and length to the same values as that surface from previous example and set its intensity to the same number of X lux, then we can say that the this light has the same "brightness" as the surface from the previous example.
Marcin Miodek | chaos-corona.com
3D Support Team Lead - Corona | contact us

2023-03-21, 13:36:11
Reply #5

Jpjapers

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I have little knowledge on light metering, but this is backed up with Wikipedia and a quick chat with our devs:

lux is illuminance (luminous flux incident on a surface)
you can, for example, spread a flux of 1000 lumens over some area
full moon has specific lux, overcast day, office area, etc

lumen is luminous flux
it is the total quantity of emitted light

Lumens are usually used to measure "light intensity" (how much light a light source emits).
Lux is usually used to measure the amount of light on some area.
Generally, lux as a unit makes little sense as a light source intensity unit.

From Wikipedia: "The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. The same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2."
^The above is also true for a Corona Light.


Let's imagine a rectangular surface which has some width and length. This surface reflects all the light it receives. We measure illuminance over that surface and we get a lux measure of X lux.
Now, if we create a rectangle Corona Light, set its width and length to the same values as that surface from previous example and set its intensity to the same number of X lux, then we can say that the this light has the same "brightness" as the surface from the previous example.

Thanks Maru, i actually did a post on what you described a few years back on someones tonemapping thread after doing a deep dive so i think i understand the difference in units and the relationship between them quite well at this point. My only real query was whether corona used the standard 1 lumen m2 = 1 lux at 1m unit as per this diagram or whether it was usingscene units but youve covered that so thank you!