On June 21st in Boston, MA, at 12:00PM clock time, the sun is 69 degrees above the horizon (known as altitude). Because of this high sun angle, the sun does not enter very deeply into the space. This day represents the highest solar altitude angles of the whole year. On every other day, the sun will enter more deeply into the space than shown here. Given that the circulation is placed at the south edge of the space with work surfaces placed more inboard, sunlight does not hit any work surfaces and will cause little glare from the disc of the sun on June 21st. In fact, the small amount of sun penetration near the perimeter increases the total illumination in the space. Approximately 93% of the floor area meets the targeted lighting criteria from daylight alone. It is interesting to note that the highest solar altitude (71 degrees) is actually at 12:40 clock time on June 21st. Due to daylight savings time, 12:00PM is actually 1:00PM and due to Boston’s easterly position within the Eastern Time Zone, the highest solar angle occurs 20 minutes “early” or 12:40 clock time.

On September 21st in Boston, MA, at 9:00AM clock time, the sun enters the space but only as deep as the circulation buffer at the edge of the south façade. The short period of time from sunrise until the pictured time can be a period of low angle glare at inboard office workstations. However, by 9:00AM the sun penetration is generally limited to the circulation way and the altitude angle of the solar disc is high enough to be of minimal concern regarding line of sight glare at inboard office workstations. Approximately 90% of the floor area meets the targeted lighting criteria from daylight alone.

Given the large percentage of the floor area that exceeds the targeted lighting criteria, one might assume that a very high proportion of the lighting energy would be saved if a high quality daylight harvesting system is installed. This may be the case, however the high level of contrast from the very bright sunlit perimeter space and the comparatively dark inboard area near the rear wall can present challenges to visual comfort and may require electric lights to be turned on near the rear of the space to compensate.

On September 21st in Boston, MA, at 3:00PM clock time, the sun enters the space, however, it is generally limited to the circulation way and the altitude angle of the solar disc is high enough to be of minimal concern regarding the line of sight glare at inboard office workstations. Approximately 96% of the floor area meets the targeted lighting criteria from daylight alone.

Given the large percentage of the floor area that exceeds the targeted lighting criteria, one might assume that a very high proportion of the lighting energy would be saved if a high quality daylight harvesting system is installed. This may be the case, however the high level of contrast from the very bright sunlit perimeter space and the comparatively dark inboard area near the rear wall can present challenges to visual comfort and may require electric lights to be turned on near the rear of the space to compensate.

On December 21st in Boston, MA, at 12:00PM the sun is still very low in the sky (24 degrees altitude) and penetrates deeply into the space. The disc of the sun is in full view of seated workers throughout much of the floor plate. Approximately 100% of the floor area meets the targeted lighting criteria from daylight alone, however this should not be regarded as successful in this case due to excessive glare from sun penetration. Blinds will need to be fully closed in order to mitigate glare.