Annual Sunlight Exposure and Spatial Daylight Autonomy


I am trying to do CBDM analysis for different types of rooms and I was wondering about the metrics of ASE and sDA.
What is generally asked it to have sDA of 300lux for more than 50% of the occupied time and
the ASE should be less than 10% of the room’s area receiving 1000 lux for 250 hours.

I was wondering how did these numbers came up? What is the backround research on these?
For hot climates would it be better to use ASE for 3000 lux if this the direct sunlight? And why they ask for 250 hours and not more?

Also, if I set the occupied hours from 4AM until 10PM I should have 6570. The analysis shows 4453 hours. The results are based only on daylight-sunlight hours and do not include night time even if you use a broader range?

Moreover, do these calculations of Useful Daylight Illuminance, Annual Sunlight Exposure and Spatial Daylight Autonomy use the three phase method? Or each one uses a different method?

Thank you for your time!


Hello Maria,

I recommend you read the standard IES LM-83-12 about sDA and ASE. In the standard is explained how they determine the lux limits and the percentages of the space. As I remember, the limit of the percentage of the area is based on a standard room. So, you need to “adapt” this percentage according to your room depth.

On the other hand, as I understand, the ASE penalty the direct light, because they assume that direct light is the main reason for glare. Then, if you have 3000 lx or 1000 lx of direct light, for the observer won’t be a difference because direct light will cause glare independent of the intensity.

The time of analysis must be work hours, but as you said, during night you won’t have problems.

I think that three phase method is enough, but you must be careful when calculating ASE because you need to set the reflectance of the surfaces 0% to take into account only the direct daylight.

Good luck with your work!