Daylight Deconstructed

The first step of the simulation determined whether the blinds are open or closed. The second step of the simulation determines the level of illumination at each point and at each hour after the blinds are in position. For LEED V4, a point must meet a minimum illuminance of 300 lux (28 footcandles) for at least 50% of the year: sDA (300, 50%).
Obtain illuminance levels at each hour using a climate-based simulation. This step is common to all annual metrics using a 10 hour per day “analysis time period extending from 8 am to 6 pm according to local clock time” (IES LM-83-12 Section 2.1.2) . The only difference with sDA is that it measures illuminance for the space with the blinds in their determined position for each hour of the day.

Process illuminance data according to the sDA metric. Each annual metric has a unique way of processing the illuminance data. The sDA metric checks each point on an Illuminance Grid to see if its illuminance is at or above 300 lux for at least 50% of the year during the analysis period with the blinds in operation. With the daily 10 hour analysis period as stated above, “50% represents 1,825 hours per year” (IES LM-83-12 Section 2.2.6).

Below, Figure 1 shows the measured illuminance for one point, and every point on the Illuminance Grid is measured this way.

Figure 1. The orange dots show the hours that the point meets the minimum illuminance threshold of 300 lux. The gray dots show hours that the point does not meet the illuminance threshold.

All of the time points that meet the 300 lux threshold are summed together and are compared to the number of time points that do not meet this illumination threshold (Figure 2).

Figure 2. Total hours of illumination above 300 lux.

The point must meet the minimum threshold for at least 50% (1,825 hours) of the annual analysis period to be counted in the final score (Figure 3).

Figure 3. Since the point meets 300 lux for 53% of the time, it is acceptable.

The final score is the percent of points on the grid that meet the minimum illumination threshold for 50% of the time (Figure 4).

Figure 4. Percentage of points that meet the 50% threshold.