Photo of one of the LED strobes from PSE used in this study.
Strobe or rotating beacon-type emergency lighting is a requirement on all Minnesota Department of Transportation (Mn/DOT) maintenance and construction vehicles. There is an effort to replace the standard warning lighting with LED-based lights in order to reduce cost of replacement and maintenance.

LEDs are well known for their long life and low current requirements, resulting in their use in a variety of applications including emergency vehicle lighting.

Top-view sketch representative of the LED lights tested in the Mn/DOT study.
However, concerns of LED-based systems include limited angularity, visibility under certain environmental conditions such as bright sunlight, and dimming capabilities during low light conditions. Because of these features, LED lighting has not been able to meet requirements for emergency lighting on maintenance and construction vehicles.

The scope of this project is to review the strobe type lighting currently used on Mn/DOT snow plows and LED replacements for that lighting. Included in the study is laboratory and field testing of the different light types in order to correlate objective and subjective test results. Lab testing included detailed optical measurements of angularity, brightness, and color for the standard and LED strobes. Field tests included visibility testing of different lights under typical driving conditions. Lights tested in this study were supplied by Whelen Engineering, Public Safety Equipment (PSE), and Federal Signal. The standard plow lighting currently used on Mn/DOT snow plows is a high-intensity discharge (HID) strobe made by Whelen Engineering.