Tuesday, May 8, 2018

Revit's Initial Intensity Settings for Lighting Fixtures

I am super excited to be speaking at Lightfair tomorrow in Chicago, on Revit Families Done Right. I will be presenting with Matt Kincaid, lighting expert and software developer at Lighting Analysts, Inc., makers of ElumTools add-in for Revit and AGI32.

As mentioned yesterday, here is some helpful information about Revit's Initial Intensity settings for Lighting Fixture families. Enjoy!

Based on Revit's Initial Intensity dialog shown above...

  • Luminous Flux = 2909.  I entered this manually based on the Luminaire Lumens that ET calculated in Luminaire manager.  This is a required step to get the Revit renderings/zonal cavity calc to work (which is a bad software design, imho). 

  • Illuminance.  By default, Revit calculates this as the illuminance due to a single fixture, at a point 10’ directly below the fixture.  Perhaps useful if you’re at Home Depot picking out new can lights for you kitchen.  But really a pretty misleading number for most situations.

  • Wattage.  Revit is taking my entered 2909 lumens, and estimating the wattage based on Revit’s default efficacy of 148 lumens/Watt (a value they pulled out of a hat, I think).  So that works out to about 20 Watts.  But, the IES file shows the Wattage is 29W.  This is from the actual test, and is the real value you want.

  • Efficacy= Should be 100.3 lumens/Watt based on the correct wattage of 29W

  • Luminous Intensity.  Basically 100% bogus.  Revit is estimating this based on the specified 2909 lumens.  The estimation is probably trying to get the intensity for nadir (directly below the fixture).  But there is no documentation that confirms this.  And, if you look at the polar plot, you can see that the Intensity for this fixture actually varies quite a bit and maxes out at nearly 1,000 candelas.

  • Check out this ElumTools video with some good detail about reporting luminous intensity; click here.

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