For the Light Pollution Reduction credit we have several questions: Question 1) LEED 2.0 states "zero-direct beam illumination leaves the building site". A formula had been submitted for the proposed revision of this Credit to determine an acceptable light level at the property boundary according to IES which is different that "zero": The formula is as follows: Ilos = (Ihor/Hlum-Hlos) X square root of (Dlum2 +(Hlum - Hlos)2), where: Ilos = The line-of-sight illuminance Hlum = the height of the identified luminaire lens above the ground Dlum = The distance from the point on the ground directly below the center of the lens of the identified luminaire to the property line Hlos = The height above ground of the typical line-of-sight at the property line Ihor = The initial horizontal illuminance at the property line due to the identified luminaire, calculated at a height of Hlos. We propose to demonstrate that we meet IES RP-33 maximum illuminance levels at the property line rather than ensuring "zero direct-beam illumination". Question 2) Do IES RP-33 Recommended Maximum Illuminance Levels call for an absolute maximum or a maximum average? This is not clear in either the standard itself or the LEED Reference Guide. Question 3) Do IES RP-33 Recommended Maximum Illuminance Levels refer to the maximum light tresspass level from any point on the site as well as off the site or only from off the site? Note that IES RP-33 refers to these values as "suggested light tresspass limitations", whereas the LEED Refernce Guide Table 1 calls these "Maximum Brightness Levels" without using the word tresspass.
1) The proposed formula is acceptable for calculating light trespass from the building site. This method adequately addresses the credit\'s intent to reduce light trespass, and can be used to demonstrate achievement of this aspect of the credit. The illuminance calculated with this method must be within the guidelines of RP-33, as also suggested by Table 1 in the V2.0 Reference Guide. Alternatively, achievement of this aspect of the credit can be demonstrated in many cases by showing that the horizontal illuminance levels on the ground at the property boundary are at or near zero, provided that the light fixtures are adequately shielded. 2) Both the formula above and the illuminance level guidelines in RP-33 are directed toward light trespass over the site boundaries. On-site illuminance levels for different design conditions should follow the appropriate standards listed or referenced within RP-33 based on use type and site conditions. The specific use of the standards within RP-33 will be addressed in the LEED V2.1 Reference Guide (forthcoming first quarter 2003). 3) The light levels listed in Light Trespass section of RP-33 are meant to be suggested light trespass limitations. When the "line-of-site" illuminance levels for the different environmental zones reach the values listed in the table, there will likely be light trespass complaints. The words "maximum brightness" as listed in the LEED Reference guide Table 1 are not proper terminology. The Reference Guide is being revised for LEED 2.1. Note that RP-33 also stresses the importance of glare control, and references other standards that address the importance of light level uniformity. When the uniformity of light ratios within a small area greatly exceed 10 or 15 to 1 (light levels in the brightest areas are ten or fifteen times higher than the light levels in darker areas) there will likely by other visibility problems that will not meet the intent of the credit. The presence of localized \'hot spots\' which exceed this ratio can call into question the success of the project\'s approach to this credit. Note that the use of uplights generally precludes achievement of this credit. Some changes to this credit were recently adopted in LEED Version 2.1. In the new credit language, the requirements of this credit are clarified with respect to fixture cut-off, overall light levels, and light spillage off the property. The new credit language will help to clarify the requirements of this credit. Applicable Internationally.