Keep getting negative illuminance value and strange UDI output in Honeybee

Hello everyone! I have encountered a big problem with Honeybee. When I tried to run an annual daylighting simulation, I kept getting negative illuminance in some sensors for certain moments. For the UDI metric, If I set the lower threshold to 0, and the upper threshold to 3000, I would get a positive value for UDI(<0 lux), which is strange. Any good suggestions? Thanks a lot.

One of my friends thinks that the way I create the room might cause the problem. Because I use the honeybee room rather than the honeybee face. In my opinion, if I want to run thermal analysis at the same time in the future, it’s better to follow the same creating method.

The relevant rhino file and gh file are attached below. Please help me with it!

Dear “Three Green” (?),

while you mentioned the front-end you are using, I do not know what daylight simulation method you apply. So I guess that you use the five-phase-method. This methods includes a substraction (low-res direct solar from global contributions) followed by an addition (result of the first operation plus hi-res direct solar). Since the results of hi-res solar and low-res solar include some noise, the result can fluctuate around zero and therefore can be negative if the ground thruth is low and driven by direct, not diffuse illuminance.

An example: true Edir=40lx, true Ediff=10lx. With some noise in the range ±30lx, you got Eglobal=20lx, Edir,low-res=35lx and Edir,hi-res=10lx. The result would be 20lx - 35lx + 10lx = -5lx for some location in a dark region of the zone. In the brighter region, the effect of such noise may be invisible.

To verify and possibly overcome this, try to increae the sampling parameters and see wether the negative values converge toward zero. If you need more help, please share information on simulation method and parameters.

Best, Lars.

P.S.: Please avoid exclamation marks and similar, non-informative decoration in subject lines. Please also note that this is a mailing list / forum covering questions about the light simulation suite Radiance, and that many subscribers (including me) have no Grasshopper installation.

Hi @threegreen, you should post this question on the Ladybug Tools forum, and @mikkelkp will be able to help you.

Using a room or building the room by faces doesn’t make a difference. They create the same Radiance model.

From what I see you are not using the enhanced method which means it will only use the total sky for the annual calculation. This shouldn’t be happening. If you re-post this on Ladybug Tools Discourse, we should be able to help you more effectively.

Dear Lars,

Thanks a lot! Also, I will try to avoid non-informative decoration in subject lines and the ladybug issue in the forum.

Hello Mostapha!I have already posted the question on the Ladybug Tools forum. The link is attached below. If there is anyone with the same problem, they can come in to have a look.