UDLI Explanation wanted

Hello All,

Can someone give me a favor to explain to me the result in the photo?

As we see, it gets less illuminance close to the window and in the middle is getting higher, and decreasing in the back of the room! Is that correct?

Also, what is the unit that comes out from UDLI 100-200 (READ_ANNUAL RESULT 1) component?

Thanks in advance,

If you check the hint of the output you’ll see the following:

UDLI_100_2000: Useful Daylight illuminance > Percentage of time during the active occupancy hours that the test point receives between 100 and 2000 lux.

From this the answer for your first question is that it can be correct. Probably, in your case, the percentage of time over 2000 lux is very high. That’s why the percentage of time between 100-2000 is lower than at the back of the space.

Makes sense for you?


Thanks @AbrahamYezioro for your reply!

you are right! when I change the range to be over 2000 lux, the light becomes close to the window.

If it’s percentage, why the result is over 1000? see the photo, you will find total addition is 1393, is it a lux or %?

How to describe the result? Can I say that “During a year, it needs more artificial lights close to a window and less in the back of a room”?

You are summing up ALL the results of the grid. This is wrong since you are adding percentages. This number is not good for you.
Also the color and legend are wrong (you see title LUX). You probably connected a legendPar to the recolorMesh.

I wont draw the conclusion you mentioned … I suggest to understand better the definition of the UDLI, what is it good for, etc.

Do you mean it needs to change it to (%) instead of (LUX), and the LUX number to Percentage number?

I have read many articles regarding to that, and understood the difference between Daylight Factor (DF), Continuous Daylight Autonomy (DAcon) and Maximum Daylight Autonomy (MaxDA), Useful Daylight Illuminance (UDLI) and Daylight Availability.
I use UDLI as a mean metric because it has 3 ranges; UDLI<100 , UDLI 100-2000 and UDLI>2000. My case is a proposed living-room in a residential building.

My problem is I got many numbers from honeybee results!! How to calculate the percentage of darkness and the lighting in this space?

Yes. Set the high bound of the legend to 100.

The UDLI is fine, then, for you. You can draw conclusions regarding where, most of the occupied hours, you have enough/not enough light, where there is a chance of glare. You can also try to change the shading conditions, depending on the results, so you not only say what is happening but you can also improve the solution.

Thanks for your reply!

I applied a shading device front of the window to improve the daylight meanwhile decreasing the energy.

Logically, whenever it has much daylight comes from the sun, it increases the heat gain into a room, therefore it increases the cooling. However, what I got when I applied a shading device in a previous room, I got the opposite result, as you see in following photos!

No Shading Device got 16946.82 kWh

with Shading Device got 17303.00 kWh.

What do you think that’s happened? Any suggestion?


From the results you show in the bottom image i can see that the cooling consumption is ~14000 and not 17303 as you wrote. If so, is is lower than the 16946 without shading device.

That’s my fault!! I uploaded the wrong result.

Please, take a look at the following images.

No Shading Device got 12960.799 kWh

with Shading Device got 13468.837 kWh.


Hard to say without checking the file. But from the images i also see that the north direction change. The last ones show that the window is in the north facade. This can explain some things …

I would share my file if you could. Which file would you want to check?


Not sure when i’ll have the time to check it, but the GH that describes the case with the geometry internalized.