Projector

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Re: Projector

Postby aoktar » Mon Apr 04, 2016 6:09 pm

aoktar Mon Apr 04, 2016 6:09 pm
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Re: Projector

Postby VVG » Wed May 10, 2017 2:33 pm

VVG Wed May 10, 2017 2:33 pm
How can one understand or indicate the equivalent of Lumen (as a built-in function in cinema4d) in the power of light?

Power =1 lumen = ?
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Re: Projector

Postby bepeg4d » Thu May 11, 2017 10:00 am

bepeg4d Thu May 11, 2017 10:00 am
Hi VVG,
OctaneRender does't use lumen, the power of light is espressed in Watt + Efficiency/Texture.
As you can see from the following link, different lights have different efficency, and have different lunem with the same Watt value:
http://www.rapidtables.com/calc/light/w ... ulator.htm
At the following link you can find a table (the second one) with different efficency values in % for different type of light sources:
https://en.m.wikipedia.org/wiki/Luminous_efficacy
So in Octane, set the Power in Watt, and change the Efgicency /Texture value according to the type of light source.
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Re: Projector

Postby VVG » Fri May 12, 2017 8:14 am

VVG Fri May 12, 2017 8:14 am
If the projector UHM lamp is 430 watts (430x4 units) (this is 20 000 Annsi lumen, luminous efficacy in lumens per watt = 46) then in the power of the octane of light you need to set the value to 430?



Is my example correct?
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Re: Projector

Postby bepeg4d » Fri May 12, 2017 2:45 pm

bepeg4d Fri May 12, 2017 2:45 pm
Hi VVG,
no, 5 is way too high as efficiency.
Please, look at this example, the first light is 430 Watt with an efficiency of 0.78.
The second light has the power in Lumen and low efficiency, If you don't want to use the efficiency, you can leave the node empty (the default value is 0.025) and use the Lumen value in the Power. As you can see, the result is quite similar:
Screen Shot 2017-05-12 at 11.08.43.jpg

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Re: Projector

Postby VVG » Fri May 12, 2017 6:51 pm

VVG Fri May 12, 2017 6:51 pm
bepeg4d wrote:Hi VVG,
no, 5 is way too high as efficiency.
Please, look at this example, the first light is 430 Watt with an efficiency of 0.78.
The second light has the power in Lumen and low efficiency, If you don't want to use the efficiency, you can leave the node empty (the default value is 0.025) and use the Lumen value in the Power. As you can see, the result is quite similar:
Screen Shot 2017-05-12 at 11.08.43.jpg

ciao beppe

Hi and thanks for the replies.

Explain to me. Where did you get the values ​​of 0.78 for 430 watts and 0.025 for 20,000 Ansi Lumen?
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Re: Projector

Postby bepeg4d » Wed May 17, 2017 10:21 am

bepeg4d Wed May 17, 2017 10:21 am
Hi VVG,
sorry my scene is heavily approximate and the efficiency value used is wrong.
I have revisited the example scene with Paride that is more expert than me on this argument, and here is the exact values to work with Lumens in c4doctane:
As said, to get the correct light in Octane we need the Watt and Efficiency values. In your Example, the light has 430Watt amd 7.3% of efficiency equal to 0.073 in octane:
LumenWatt_01.JPG

Now let's say that we have the only the Lumen value, that, accordingly to this calculator, for your light should be 430 x 50 lu/W = 21.500 Lumen. To obtain the same light knowing only the Lumens value, we need to use the Lumen value in Power, and 1/683 = 0,001464 in the Efficiency float value:
LumenWatt_02.JPG

The Lumens-Watt translation is quite complex and involves also the temperature and the Normalize parameter, but for a general use, this conversion should be more than enough.
Let me know if it works also for you.
Happy rendering,
ciao beppe
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Re: Projector

Postby VVG » Wed May 17, 2017 6:54 pm

VVG Wed May 17, 2017 6:54 pm
Hi, bepe
Now I understand you. Thank you

A magical value of 683, need to remember everything ))
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