Tersen supplies LED fixtures for Mall Of America garage retrofit

The Mall of America in Bloomington MN, the most visited mall in the US, has installed new LED fixtures from Tersen Lighting replacing 5600 HID lights in two seven-story parking garages that house 12,550 spaces. The city of Bloomington has extremely strict codes for light levels and uniformity, and Tersen's Ratio family from Acuity Brands turned out to be uniquely suited for the application.

Throughout most of the US, 2.5 fc is considered a safe level of light for parking ramps. Bloomington requires 5 fc with a maximum to minimum uniformity of 6 to 1. Alternatively, the requirement drops to 3.25 fc if the installation meets a uniformity goal of 1.5 to 1.

"For the mall, we have both horizontal and vertical minimums," said Londell Pease, planner with the City of Bloomington. "We wanted to make sure that the light levels were bright enough for security reasons and have a good uniformity across the space."

Cutoff fixtures

The city also requires a 90° cutoff in the fixture design meaning that the fixture has no uplight as measured according to the backlight, uplight, and glare (BUG) classification system defined in the IES TM-15-11 standard. For more information on BUG ratings and outdoor lighting, view our recent Webcast on the topic.

The cutoff requirement was also meant to eliminate glare. "The city determined that all new outdoor lighting fixtures needed to be cut-off fixtures to help with glare," said Charlie Brantl, project leader for the Mall of America. Pease added, "As we get older, our eyes don’t adapt like they used to. Transitioning from bright outdoor light into a dark parking garage means there is less chance for the eyes to adjust. We wanted to eliminate any hazard associated with vision."

Brantl said that the mall wanted to achieve a four-year payback on the lighting project so low-energy lights were a requisite. The mall considered a transition to linear fluorescent lights, but that would have required a doubling of the number of fixtures, and the goal was a one-for-one fixture upgrade.

Aesthetics and evaluation

Over four years the team evaluated numerous fixtures from more than 15 manufacturers. The mall had one additional aesthetic requirement that the fixtures be round in shape. Ultimately lighting-design firm Davis & Associates essentially custom designed a fixture for the mall working with the Tersen team.

"In developing the fixtures, we knew energy savings was a key factor right off the top, as the majority of the lighting remains on 24/7 due to the ramps sizes and depths," said Shawn Meyer of Davis & Associates. "We then needed to focus on pairing these energy saving goals with fixture performance and the criteria set forth by the City of Bloomington."

The project was primarily accomplished using Tersen Ratio PG LED luminaires that are ceiling mounted, round, and integrate multiple LEDs with total internal reflection (TIR) lenses on each to control the beam pattern. There were also some surface and arm-mounted Ratio luminaires used in the project.

Project scope

The project encompassed parking ramps, entryways, interior parking, stair wells, and top decks. The incumbent lights were 150W high-pressure sodium (HPS) fixtures and 175W metal-halide (MH) fixtures. The 5600 new Ratio fixtures are rated at 55W.

"Tersen Ratio PG LED luminaires achieved the highest reduction of wattage that still met all of the City’s requirements," said Brantl. "The uniformity of the Ratio PG LED fixtures came up 1.38 to 1, which is very good and uniform. We now have five to seven foot candles everywhere across the space."

The lighting levels and uniformity will pay dividends in better safety and security. "In the transit center, with the previous fixtures, we were getting about 2.5 to 3 fc at eye-level,” said Pease of the city. "Now we [have] closer to 8.5 fc with the Tersen Ratio PG LED luminaires. Rather than just having the uniformity on the ground, we actually have outstanding uniformity five feet up."

Pease's point about vertical illuminance is another one addressed in the previously mentioned outdoor-light Webcast. Vertical illuminance is more important than horizontal illuminance in detecting objects and faces.

"With the new fixtures, the depth of field on closed circuit television is outstanding, which really helps with security," said Pease. "The police need to be able to identify subjects on their monitors, as well as when confronting subjects in person, so reducing the amount of shadows and glare is important. There were lots of shadows and glare caused by the previous fixtures, but now we have a wide open look at each ramp."

Energy savings

Of course energy savings was a key motivator for the project and the lower-wattage LED products deliver those savings. The mall retrofit team has projected an annual savings of 7 million kWh. The mall does expect those savings to deliver the projected 4-year payback.

The project also delivered on the goal of reducing light pollution as you can see from nearby before and after pictures of the garage.

"One of the things that shocked me about the Tersen Ratio PG fixtures was the lack of light pollution from the highway. When driving by, the lights did not appear as one large glaring light source like the old fixtures did," said Pease. "I initially thought there was no way we were getting the required foot-candle levels, but was baffled when we measured the performance. The light levels and distribution with minimal glare was unlike any other fixtures I have seen, and I looked at more than 20 different LED light fixtures throughout this review process."