Lightbar Rotator Speeds

[bmd224]

Question: On lightbars, why do manufacturers (especially Code 3 on the MX-7000) place the slow rotators on the outside/ends of the bar, and the fast rotators on the inside/middle of the bar?
I always thought it should be the other way around, so more flashes occur at the sides of the bar where usually only one rotator is visible while crossing or 'breaking' an intersection.
Any thoughts?

 

[SBFD-E-9]

It could have been the way it was speced. Usually I see the outer and center rotators fast speed, and the inner rotators slow speed.

 

[dmathieu]

The thinking back in the day was, the slower rotators were considered optimum to the human eye (longer dwell time) for distance and identification of a vehicle. These were put on the outside to mark the tracking, width, and position of the vehicle at those longer distances. The faster were used for eye catching purposes, but with less dwell time, were considered less effective for long distance warning/identification.

 

[NPS Ranger]

At one time SAE J845 specified the allowable flash rate for rotating lamps, something like 80 - 120 flashes/minute. For a lightbar to be considered compliant the end rotators had to be within that spec, because from some angles the end was all you could see. Fast rotators could be used elsewhere within a fullsize bar, but for example you couldn't have an SAE compliant minibar with 2 fast rotators. Some states still have language specifying flash rates. Once strobes came along with comet flash and multiple patterns, the SAE standard was revised several times. At that point we began to see a lot of high speed rotators in minibars and beacons, which have been standard in Europe for decades.

 

[lite-em-up]

SAE requirements... In order to meet the required light output for a 360 degree warning system, the rotators could not spin so fast because it would be a less effective signal. So in order for a bar to meet SAE the outboards would have to be standard and all others could be whatever you wanted. The bar met SAE with just the outboards.

 

[SEPD_52]

I thought the SAE J845_201306 specs were that the flash rate must be "at least 1.0 Hz (60 fpm) and no more than 4.0 Hz (240 fpm)"? Has that been changed? I'm curious to know why some flash patterns are not SAE J845 compliant but are NFPA 1901 compliant.