Interstate 35W Bridge Collapse
August, 2007, Minneapolis, Minnesota

A Somber Kelvin Case Study.
Eleven years ago, the Interstate 35W bridge over the Mississippi River in downtown Minneapolis collapsed, in a tragic accident that killed thirteen people and injured 145 more as cars, trucks and a school bus plunged into the Mississippi below.

This Bridge was rebuilt and many things were done differently afterward, with a primary focus on SAFETY. One notable change is seen in the above animation from a photo taken at night of the new LED light fixtures.

The twenty 400 watt High Pressure Sodium Lights (2000 Kelvin) on the old Bridge were replaced by twenty 290 watt LED Light fixtures (>5000 Kelvin) on the new Bridge which produced a different and safer color of light.
A comparison of the ‘before’ and ‘after’ light fixtures on the two Bridges:
  • The Kelvin of the lights increased from 2000 Kelvin to over 5000 Kelvin.
  • The lumen output of the fixtures decreased:
  • High Pressure Sodium bulb output (40,000+ lumens) was reduced with the new LED fixtures (16,500 – 19,000 lumens).
  • And - the night visibility of those driving over the Bridge was changed.

An actual Survey taken of the Drivers on the Bridge showed:
With less lumen output, why did the new LED lights
seem brighter to the drivers?
The Human Eye ‘sees’ light differently at night.
Don't miss our next Technical Journal (#50).
"LED Lighting and the Human Eye."
Bill Nagengast, Lighting Engineer
Solas Ray Lighting
Holds over 20 patents in the lighting industry.
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TJ-49 11.01.18