Prescriptive Method Questions Cont'd

The LEED 2009 Reference Guides prescribe a minimum and maximum daylight range for the first 2 calculation options. For option 1, it is a range: minimum 25 fc and maximum 500 fc. For option 2 the range is between 0.15 and 0.18. For these options, I would assume that if you exceed the threshold, you cannot count that bay as the guide has put a maximum cap. However, option 3 - actual measurement with a light meter- doesn't mention anything about a maximum foot candle requirement as long as your spaces measure a minimum of 25 fc. You might be able to use the combination option 4 approach and prove compliance using the calculation methods for all spaces you know fall within the minimum and maximum ranges, while taking actual light meter readings for the areas where you think you are exceeding the ranges.

If you have a room where the rough calculation (option 2 - prescriptive) indicates high brightness at the glazed wall, this LEED benchmark is indicating that there is a potential problem with glare (due to the high brightness ratio). The design team would be well served to reconsider the transmissivity or area of the specified glass at that space. If neither can be changed, consider providing automatically controlled glare control translucent shades (to maintain views) and using option 1 (simulation) for your calculation (computer simulation) to comply with the credit. Option 3 (measurement) also requires avoidance of high contrast (though it's vague about measuring this).