Light Shelf Daylight Modeling not Working

Hi, I am trying to model light shelf to make a daylight penetration to deeper area of a room. However, it might not doing so. I have increased the ab to 4 and ad to 1000. However, when the length of lightshelf increased from 0.5 to 1 daylight autonomy decreased. I also changed the ceiling reflectance to 0.8 but the problem still occur. I am trying to get light shelf example file on old topics but the file does not exist. Please help, the file and weather data is attached. (784.5 KB)

hi @aishanuraaa

Interesting topic. Please do post some screenshots of the case and problem that you are facing.

A lightshelf would cast shadow below, near the window… maybe the Daylight Autonomy there could decrease, but perhaps at the end of the room the levels are distributed deeper?

What material have you assigned to the light shelf? most likely that high reflectance is needed >0.9 and some specularity. Have a look here for a database of materials

Let us know.

Hi,@OlivierDambron is a very nice material database. Thanks for your share!!!

From my understanding, under diffused sky condition, the light-shelf’s performance is reduced. At certain point, the tradeoff between light redirection/casting shadow is simply not worth it and the light-shelf would be counterproductive.

This is something I’ve found out while dealing with tropical climate, especially during the rain season where there’s a lot of cloud.



In my experience, light shelves aren’t nearly as effective as their popularity suggests they should be. My guess is your results are correct, but I’m curious what others think. A design space that explores orientation, cloudiness and glazing ratio would be really interesting for everyone to see. Has anyone created one?

Hi, thank you all for your response. I think there are several studies that has investigate the use of light shelf in tropical climate. I put the reference down below.

2016 The Effectiveness of Light Shelf.pdf (874.1 KB)

Thanks for the paper @aishanuraaa

I ran a design space over the weekend to explore the topic and test the approach of using Honeybee to quickly explore common questions. Anyone can review the results here:

Parameters Tested

  • Façade type
    • Full curtain Wall
    • Ribbon window with lower portion solid
    • Punched Window
  • Location
    • Detroit (cloudy)
    • Phoenix (sunny)
  • Clerestory Height (light shelf height from top of window) (3x)
  • Clerestory Depth (4x)
  • Orientation (8x)

It appears that light shelves reduce overall annual daylight levels. This apears to contradict the common idea that light shelves bounce more light farther into the space. However, this model does not incorporate internal blinds. As shown in the study @aishanuraaa linked, when light shelves block overlit conditions and allow blinds to remain up, overall light levels may increase relative to the shades-down condition. Light shelves therefore may still be an effective solution for improving daylight quality even if they do not on their own increase daylight quantity.

Taken from the conclusion of the paper:
“The findings concluded that the integration of light shelf and partial blind at sitting position eye level is the most effective design for contemporary high-rise open plan office. Therefore, internal shading shall not be overlooked or simply left to the office users to install without proper understanding in daylighting. Architects and interior designers shall take internal shading into thorough considerations even during the early design stage towards achieving effective tropical daylighting.”