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Render Absolute Photometry Correctly Out of the Box (LED Lighting)

Render Absolute Photometry Correctly Out of the Box (LED Lighting)

When LED light fixtures are used in Revit, the rendering engine does not properly interpret the IES file. It works correctly if you render in the cloud, but for some reason the out of the box render engine interprets the light as rainbow colors.

25 Comments
jill_chen
Autodesk

Does anyone know if there is standard conversion method for lumen to candela (or candela to lumen) for absolute photometry lighting? or how does candela used for the absolute photemetry lighting (e.g. LEDs). Thanks a lot!

Anonymous
Not applicable

@jill_chen The answer is a giant formula that I cannot understand that is located in the IES handbook around page 600-ish if I remember correctly.

https://www.ies.org/store/lighting-handbooks/lighting-handbook-10th-edition/

 

Realistically speaking there are two options. Either Autodesk will integrate this formula into Revit so that it can determine how many lumen are in the light or people should use the very obscure website I provided to get the lumen amount:

https://www.visual-3d.com/tools/photometricviewer/

 

Maybe you can also figure it out if you understand steredians:

https://www.ies.org/definitions/candela-cd

 

Also, anyone working in a photommetry lab (the people who create IES files) would know how to answer this simply.

ArmandD
Enthusiast

Jill,

 

Here is some information that explains how to calculate the total luminous flux from an IES file. 
See this article:  http://resodance.com/ali/zl.html

Key point to look at in the article:
The following paragraph is referring to the Vertical angles in the IES file.
"A more general equation - used to determine the solid angle between two cones with the same centerline - is 2pi * (cos(small angle) - cos(large angle)), which produces the values known as zonal multipliers (e.g. in the IESNA Lighting Handbook), used to convert luminous intensity to luminous flux."

Further down in the article he discusses the horizontal angles.

Armand

Anonymous
Not applicable

I suggest you hire a lighting consultant to do audit and make recommendations on the lighting aspect of Revit. Autodesk has been doing an amateur job poking its nose into light for many years now, but they do not understand what they are doing and are not providing us with the things we need. by getting a professional and/or a lighting designer, you could get some real progress in this and identify all the deficiencies in the lighting system (there are many).

 

Once all the problems are solved, you could also start working on all the things that we need to do proper lighting. By getting people who don't know about lighting working in this, you will be stumbling around.

 

I would recommend Ian Ashdown, he is a digital lighting god

https://ca.linkedin.com/in/ian-ashdown-2671754

mthomas45
Advocate

Has there been any progress on this front?

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