ID#5245 made on
SSc8 - Light pollution reduction
LEED BD+C: New Construction, LEED BD+C: Schools, LEED BD+C: Core and Shell, LEED O+M: Existing Buildings
Our project is located in the heart of downtown Allentown PA and falls under the lighting category "High Ambient Brightness." The site comprises an eight storey building, approximately 140 i...
Our project is located in the heart of downtown Allentown PA and falls under the lighting category "High Ambient Brightness." The site comprises an eight storey building, approximately 140 in height above grade, and a plaza in front of that building. The plaza is bordered by city streets and sidewalks (not part of our project site), with city standard historic pole mounted fixtures. These fixtures are not cutoff fixtures and distribute light in a radial pattern towards the street, the sidewalk below, and towards the plaza. Our project's landscape lighting scheme is designed to balance the perceived brightness from these city street lighting fixtures by utilizing up-lit trees within the plaza as glowing objects that replace the need for additional pole mounted fixtures. Additionally, the plaza incorporates a fountain with up-lit water jets to enliven the plaza at night and add to the perception of the plaza as an occupied public space. Aside from the trees and fountain, all other plaza lighting, and the light levels eminating from the adjacent internally lit 140' high building, are clearly within proscribed low-level light standards proscribed by the LEED 2.0 Rating System and its associated credit inquiries. We would like the USGBC to confirm that the up-lighting scheme for these plaza trees and fountain conforms to the revised lighting requirements specified in the LEED 2.1 Rating System and thus the general intent of this credit to eliminate light trespass, improve night sky access, and maintain a safe and appropriately lit urban public space.
Beginning with the trees, which are the primary lighting component of the plaza, they are nominally 16' to the top of the canopy. The illuminated undersides of the canopy at this pedestrian scale would significantly contribute to the public perception of a safe environment. Based on detailed computer modeling of the proposed tree lighting scheme, we find an average light level of 2.0 fc directly above the tree canopy when lit from below by the specified recessed up-lighting fixtures. As an additional note, the source is regressed within the fixture suspended from a cast iron tree grate cross louver providing superior cut off shielding of the source. Based on the foot candle levels above the tree canopy, and especially when put in the context of the adjacent street lights and the neighboring tall building, the lighting of these trees meets IESNA standards for low level exterior lighting and we believe that there is effectively no stray light adversely affecting this urban setting.
The second area of up lighting in the plaza is the fountain, which comprises water jets that are lit from below by parabolic luminaries. The light fixtures are provided power only when the fountain pumps are active, so there would be no circumstance in which the lights would operate without a water column above the lamp to shield the light source. The effectiveness of the water as a light shield was determined in a measured study of the fountain light levels, which recorded an average light level of 9.06 fc three feet above the water feature when utilizing a 50W MR16 source. The design calls for a 35W lamp instead, which should reduce the measured average light level above the fountain to approximately 6fc. As a note, the luminaires are less than 3500 lumens and do not require full cutoff shielding; because each fixture is recessed well below the level of the paving, the full intensity of a lamp would never be visible since there will always be a column of water atop it. Accordingly, we believe the fountain lighting levels are well within the IESNA standards, especially as the fountain is located between the unshielded city street lights and the 140' high illuminated building.
Please confirm that these two plaza elements with their carefully shielded up-lit elements meet both the specific requirements of LEED 2.1 SS credit 8, and the larger intent "to provide enough illumination for safety, accessibility and public perception while at the same time avoiding unnecessary light pollution."
Under LEED v2.0, uplights are precluded in achieving this credit, as they represent direct beam illumination to the night sky. Under LEED v2.1, clarifications have been made that allow some limited uplighting, primarily for the purposes of lighting the American flag at night.
In areas of high ambient brightness only, limited uplighting will be allowed if the following conditions are met: (1) All credit requirements are met, including full cut off luminaires for lamps over 3500 initial lumens and shielding for those over 1000 initial lumens. (2) Lighting controls are used to turn off lighting after hours and/or during post curfew periods. A plan should be developed to insure the use of the controls (automated controls, etc.). Note that some landscape features such as trees and plants (depending somewhat on the type of planting) require a rest from light. (3) Lighting controls are commissioned.
In addition to the above conditions (and associated documentation), certain additional information must be provided to demonstrate compliance with the credit intent: (1) The results of a light study that verifies the illumination intensity emitted directly above the feature being lit (in this case, the fountains and the trees). (1a) If trees are being uplit, this study must verify the maximum light levels that will be produced when the trees have dropped all of their leaves. (2) A narrative describing how light levels and glare will be controlled around the trees in each of the seasons and listing the hours of intended uplighting operation for both the water feature and the plaza tree lighting. (3) A statement from your landscape architect indicating that the planned tree lighting will not have adverse effects on the trees' dormancy cycles. (4) Confirmation that the fixtures and lamps installed are the same as those modeled.
Note: the v2.1 Reference Guide language will provide further clarifications; please refer to that document before finalizing your design.
Related Addenda (Corrections & Interpretations)