Light shelf not doing what it should?

Hi all

I have been modelling a simple room with a light shelf for a small study that I am doing. I am not quite sure that the results I get are accurate. Maybe someone here can share their wisdom :slight_smile:

I have modelled the room to have both an internal and external light shelf. The external shelf can be angled so that light should be reflected further into the room, which it does indeed do, but to a very limited extent as can be seen in figures 1-3 (this is a vertical WP in the YZ-plane):

Figure 1 - No light shelf:

Figure 2 - Flat lightshelf:

Figure 3 - Angled lightshelf:

The thing that seems a bit strange to me is that the light shelf seems to do more bad than good. It provides shade to the area closest to the window, thus reducing the illuminance in that area, but doesn`t reflect the light as much as I thought it would. As I said, setting the external shelf at an angle has some positive effect, but not at the back of the room which is the part that should be benefitting from the light shelf. Also, I would have thought that keeping it flat should also do some good.

I have set reflectance parameters to quite high values in attempt to get the light into the room, but it does not have the effect that I hoped for. The reflectance values for the ceiling and the light shelf are also set to values quite a lot higher than on the floor, but the floor still seems to reflect better. The dimensions of the room are: width = 3m, depth = 6m, height = 3m.

What could be the problem? Help is much appreciated!


Attached is the gh file (with a horizontal work-plane) and the compressed results files if you don`t have the patience to run the simulation.

The gh file follows the example of M. Roudsari`s β€œgetting started files” to Honeybee. Simply toggle β€œ2” to true and press β€œ3” to run all the simulations. If you edit the input list in β€œ1”, be sure to change the max values in the sliders as well. Finally, you can visualize the results by dragging the sliders in 4. (230 KB) (524 KB)

Not exactly wisdom but i would recommend to increase the -ab radiance parameter to al least 4 (default is 2). This is the one in charge of calculating the number of bounces for indirect calculation. Which in your case is critical.

Probably the -ad parameter also need an increased value (default 512). test it with 1024.


Hi Orn,

As far as I can see in your example lightshelf does what it is supposed to do: 1. scatter the light into the space and 2. Shade the surrounding area. You should have a more even distribution of the light with lightshelf.

There are some parameters that you can change to have a better idea from the effects of your lightshelf.

  1. I would make the room deeper so you get some dark space at the end of the room.

  2. I would make the room wider while keeping the test grid in the center to avoid the effect of the side walls. You can also assign black colors to the side walls.

  3. Set a view from inside the room and render the images. You will see how lightshelf changes the daylight pattern inside the space. Creating false color images also helps for an easier to understand visualization.

  4. Now try it for different times of the year to see the effect of the sun angle (both on the grid and the images).

  5. Finally run an annual analysis with and without lightshelf.

Setting the parameters to a higher quality will mainly change the results at the end of the room. As Abraham mentioned for this case you need to increase the number of bounces.


Thank you Abraham. I will try this when I have time to look at the model again :slight_smile:

Thank you Mostapha. As always, very helpful! I will try this when I have time to look at the model again :slight_smile: