Revit MEP - Light Levels

Jason Combs a P.E. (Professional Engineer) with Woolpert, Inc. was worried about me. He noticed that I hadn't posted in a couple days and sent me this so I could keep on track. Okay, okay I may have stretched the truth a bit. He wasn't worried about me but he did share this information with me the other day and it seemed so nicely put together that I might as well just put it here too. He said it was okay so here it is!

Jason writes:

Adjusting the elevation of a light inside of a space will change the lighting level in the room. Following is a significant set of characteristics affecting the way lights work in a room/space.

Light families must have a light source to add illumination to a room. In other words, in order to schedule the estimated illumination of a light, a light source must be added to the family through the Categories and Setting dialog within the family.


The illumination in a space is related to a light family's Illuminance. But don't be confused when scheduling Illuminance versus Illumination. Following are two schedules, one is a Light Fixture schedule and one is a Space Schedule with Lighting fields included. Illuminance of a light is based on a given foot-candles amount at a given height (i.e. 10fc @ 10'). Illumination in a space is dependent upon the number of lights and at what level the measurement is taken for a given set of light Illuminances.


The Light Source location is what matters when it comes to measuring the illumination in a space. The following image depicts that the light source is within the space. However, there is an unclear limit to where the light source must exist within a space. After some testing, I (Jason) determined that the light source must be within 1'-0" of the space and exist on the same side of the work plane to included in the space. Further I (Jason) was able to adjust the tilt angle of the light source from -90 deg to 0 degrees and still existing within the space.


Without the Light Source visible it would appear that this standard troffer light in the following image is outside the space. But no, Revit still considers it to be within the space because the light source is within 1'-0" of the space even though the visible geometry is entirely outside. Just remember to keep the light source within the space!


Here's an example illustrating that the Light Source location affects lighting calculations. Flipping the work plane of the light can significantly change the illumination value in a space.


In the following example it appears that Adjusting the Tilt Angle of the Light Source did not change the illumination calculation within the space.

Thanks for sharing this Jason!