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Page 1 of 2 <br /> <br />DATE: February 13, 2017 <br /> <br />TO: Honorable Mayor and City Councilmembers <br />William S. Joynes, Sr., City Administrator <br /> <br />FROM: Sue Polka, Interim Asst. Public Works Director/City Engineer <br /> <br />SUBJECT: County Road E Bridge Lighting <br /> <br /> <br />Requested Action <br />Accept proposal from Forest Lake Contracting, Inc. for the removal and replacement bridge <br />lighting at the County Road E Bridge at Snelling Avenue in the amount of $6,999.00. <br /> <br />Background <br />Two decorative light fixtures currently provide light to the County Road E Bridge over Snelling <br />Avenue. The existing lights do not provide the recommended foot-candle levels for a concrete <br />sidewalk in a commercial area (0.9 fc). <br /> <br />Discussion <br />WSB & Associates has provided photometric plans for three lighting scenarios: no lights, <br />existing lanterns, and LED shoebox lights (Attachments A, B, and C). These show that replacing <br />the existing lanterns with the LED lights would provide adequate lighting in accordance with <br />standards for sidewalks in commercial areas as well as provide lighting for the bridge deck. <br /> <br />Light Loss Factor (LLF) is the factor by which light output is adjusted due to a combination of <br />environmental factors and luminaire degradation. The LLF compares lighting output in a <br />laboratory condition to output in actual field conditions. The factors include: <br />• Lamp Lumen Depreciation (LLD) – the overall performance of the lumen output over a <br />predetermined time period (of the at 40% of expected product life). <br />• Luminaire Dirt Depreciation (LDD) – the light loss due to dirt, road salt, etc. expected on <br />a fixture that hasn’t been cleaned. <br />• Luminaire Ambient Temperature Factor (LATF) – the effect the ambient temperature has <br />on lumen output. The higher the ambient temperature, the less lumen output. <br /> <br />For the photometric analysis of the existing bridge lighting and the proposed bridge lighting, an <br />LLF of 0.89 was used. This provides for a similar comparison of the two fixtures and mounting <br />conditions. The lumen output for the proposed lights will be brighter than the photometrics show <br /> <br />CONSENT ITEM – 5I <br /> MEMORANDUM <br />