This document provides design guidelines, test procedure references, and performance requirements for stop arm lamp devices on school bus vehicles which are used to alert traffic to stop when passengers are loading and unloading
Photometric performance has now been established as meeting the original peak intensity and meeting a specified “optical power”. Advances in laboratory instrumentation have made it practical and cost effective to directly measure the optical power generated by any optical warning device. The direct measurement or calculation of peak intensity also is readily done with current technology. The Minimum Peak luminous intensity values are the minimum luminous intensity values from the previously published recommended practice. The Optical Power values were calculated from the Candela-Seconds values multiplied by 60 s to obtain cd-seconds/minute with the minimum flash rate of 1 flash per second.
Source definition has been changed to include multiple source components with some restrictions. Light pulse and flash definitions have been added.
Optical power has been defined.
Multiple flash patterns and cyclic patterns have been added. End users have been requesting non-repetitive flash patterns to prevent complacency.
The specified minimum size lighted area has been eliminated. Recent demonstrations have shown that observers were unable to see any difference in the performance of flashing warning devices having the same optical power but substantially different lighted areas.
Environmental tests have been added – these include low temperature, high temperature and 200 hour durability flash rate maintenances.
The flash rate range was increased from 1-2 Hz to 1-4 Hz. Increasing the flash rate without a corresponding increase in photometric energy lowers the flash energy. However, if the flash rate is increased and the photometric energy is maintained above the minimum requirement, the conspicuity of the signal is improved. From a practical stand point, higher flash rates reduce the travel distance between signal flashers and promote earlier recognition of a hazardous condition. This document increases the allowable flash rate maximum to 4 Hz, so long as the flash energy content of the signal is not reduced below the required tabulated values. It is important to note that the energy to operate such devices may have to increase with the flash rate.
Miscellaneous Editorial Changes – The word “device” is used to indicate the assembly of components which is tested. The previous edition used both the words “lamp” and “device” for this purpose as well as referring to light sources as “lamps”.
Removed Design requirements since this recommended practice is for the lighting devices and should not specify reliability requirements for mechanical components
Remove reference to SAE J887 since there is no need to reference the other Recommended Practice
Change from SAE J575 to SAE J2139 for environmental testing for vehicles wider than 2032 mm. The typical application for these devices is for school buses which are over 2032 mm in width
Added reference to SAE J387 and SAE J1330 SAE publications
Added 300 cd maximum for Figure 1. The lights are installed at other vehicle driver’s forward looking position and need to ensure lights are not too bright.