Diagram: Annual Sunlight Exposure

Annual Sunlight Exposure

ASE gives you a feel for how excessive sun affects your space in terms of glare and solar heat gain.

The following was posted on the Arch Lighting website

ASE A Proxy for Glare and Overheating

With higher levels of daylight sufficiency comes the potential for glare and solar heat gain. That’s where Annual Sunlight Exposure (ASE) steps in. Meant to complement sDA, ASE is intended to help designers limit excessive sunlight in a space. While ASE is a crude proxy for glare phenomena, it measures the presence of sunlight using annual hourly horizontal illuminance grids rather than luminance measures, so it is technically not a glare metric.

ASE uses a simulated 1,000 lux as an indicator value for sunlight, but the simulated value can differ significantly from what is measured in the physical world, which considers secondary bounce-off surfaces. Like sDA, ASE values range from zero to 100 percent, with the latter suggesting that the entire floor area of the space in question exceeds the simulated value of 1,000 lux for at least 250 hours per year. Thus, to reduce the potential for glare and thermal stress, designers should aim for low ASE values.

LM-83 provides preliminary guidance for recommended ASE limits, cautioning that spaces with ASE values exceeding 10 percent will likely result in visual discomfort. The DMC is presently refining the criteria for recommended practice of interpreting ASE results, but designers can use ASE immediately to make relative comparisons among proposed design options. In the future, the DMC will provide better criteria to guide absolute performance thresholds using ASE.

The sunlight analysis method implemented in simulations using LM-83’s methodology to calculate ASE is also used to trigger the human operation of manual blinds, which affects the determination of sDA. As a result, areas with high ASE values may have lower sDA scores because the algorithm assumes building occupants will close window blinds or draw the window shades manually if excessive sunlight persists.

 

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