Lighting Calculation Luminaire Plane

[HVAC-Novice]

i know Revit has the limitation that the Lighting Calculation Luminaire Plane is set by the lowest fixture. IS there a workaround to trick fixtures into not being seen a fixtures?

In a high-bay space I added an Exit light and the plane came down to 8'. I noticed when I move the light source in the EXIT family up (as it dosen't contribute to light anyway) i can trick Revit in not using the EXIT light as the lowest fixture. Deleting the "light source" didnd't work.

In some applications I have low-level floodlights, or step lights etc. So those could bring that Calculation plane close to floor level. Which obliviously will make things very wrong. Is there a way to make a light fixture to not be counted for the purpose of determining that calculation plane? I don't want to convert them to a different type of family.

I know Revit isn't a complete lighting software, but the Revit lighting tool is handy when doing a first layout.

[Alaaeldin_Alsahli]

light Calculation is not my strong field, but if you assign these step lights to a workset and turn them off during the light calculation, does it work?

[HVAC-Novice · Accepted solution]

Putting them on a different workset and "hide" the workset doesn't change the Calculation Luminaire plane. It also wouldn't help me if it did since i schedule the calculated fc-values (to show I meet IES or other requirements). Playing with worksets would mean when i print the sheetset to repeat that procedure (since "hiding" workset also would hide the fixtures on the plan).

What I came up with is:

- lay out lighting in Revit so that it kind of illuminates the way I want (and include the experience gained from below)

- export that view as dwg to my lighting software and perform lighting calc there and adjust lights as needed.

- then edit light fixtures as needed to match the layout in lighting software.

- This can give me much different fc-values in Revit. Espeically whne i have high-bay fixtures, but one fixture very low, the REvit value can be twice as high. My trick is to turn off some fixtures in Revit (turn off "Calculate Coefficient of Utilization" checkbox) until the Revit fc-values match the values in my lighting software (I use Visual)

I noticed in rooms where the calculation luminaire plane is correct, Revit is spot on (with same reflectance values, lumen values and lightlossfactors). We talk about 31 vs 32 fc values. Really great. But where there is a large difference in plane height, values drift off. It would be great if a new Revit version would fix this since it has potential to be useful for lighting design.

With the above knowledge, experience with the fixtures, and tracking W/ft² values one could get a pretty good layout, but still want to verify in a detailed lighting software.

[aksrocks]

Hi. I'm facing the exact same issue. Revit calculates lighting pretty accurately except for spaces where there is lighting fixture family (even without a light source) and even if Calculate CU is turned off. Revit will just not exclude this fixture from being included to calculate the Ligthing Calculation Luminaire Plane and thus the Room Cavity Ratio Calculations. This completely throws off the Illumination calculations and makes the whole thing useless. In contemporary design where we have LED Strips and Low Level lighting all over the place, a simple checkbox to include/exclude fixtures from ligthings calculations would have done the trick.

Does anyone have a work around?

[fabiosato]

Hello,

Select the Lighting Fixture and set Coefficient of Utilization to 0.

[aksrocks]

Thanks for your attention to the matter, however this does not work.

Revit says, "The value for Coefficient of Utilization must be between 0 and 1."
And like I mentioned in my earlier post, switching off the CU for the fixture or giving it a value close to zero can only allow us to control whether the lumens produced by the luminaire contribute to the Average Estimated Illumination (AEI). This however still screws up the calculation of AEI for the entire space because Revit determines the Ligthing Calculation Luminaire Plane (which is used in the formula for arriving at the Room Cavity Ration and hence the CU) merely by the presence of a lighting fixture family irrespective of the fact whether the family contains a light source or not or CU set to off/zero or not.

Now, the critical aspect to note here is that this value of Ligthing Calculation Luminaire Plane which is reported in the properties of the space, is used by "ALL FIXTURES" to calculate their individual CUs as revit uses the height of the lowest fixture to set the value for the Ligthing Calculation Luminaire Plane.

To make it absolutely clear, lets say Fixture A (4000 lumens) is set at a height of 10' from the floor and Fixture B(100 Lumens) is close to the floor at 1'. Now, obviously Fixture B doesnt contribute to the lighting level at my workplane height of 30" so I set it to not calculate CU. However, Fixture A now calculates its CU by using the Room Cavity Ratio which is obtained using the mounting height of Fixture B, which will be negative in this case as the workplane height is above the fixture height. The result of this is that revit ends up with an extremely high and incorrect value of CU, maybe double or more. And thus, this space whose correct AEI at workplane level should have been 500 lux will end up being calculated as 1000 lux or even more.

This is at the core of lighting calculations and revit makes this entire process useless just because they dont have a simple tick box. Now, I've tried assigning these fixtures which should not contribute to ligthing calculations to a separate workset and then closing that workset. However, revit still includes this fixture into lighting calculations.

I'm left wondering how does a software so advanced miss out on something so basic. Or am I missing a trick here? Can someone please guide me?

[HVAC-Novice]

Thread necromancers of the World:

The whole lighting calcaultion in Revit is pointless for professional lighting design. i've been using elum tools plugin for many years and it is perfect. 

Yes, it cost money, but you get what you pay for and if you design lighting for money, you shouldn't use the oob Revit lighting tools. IMHO the Revit lighting tools give you a rough estimate at best. Even if you can work around this luminaire plane issue.