SAE J887_201106

This document provides design guidelines, test procedure references, and performance requirements for red and yellow overhead warning devices on school bus vehicles which are used to alert traffic to stop when passengers are loading and unloading. Manufacturers are now integrating flashers into the lamp. Environmental tests for flash rate have been added. Added references to FMVSS108, CMVSS108, SAE J387 terminology, and SAE J1330 laboratory accuracy guidelines. Added reference to SAE J578. This was added to ensure consistency with other SAE lighting documents. Added definitions for: Light source, Light Pulse, Optical Element, Optical Power, and flash. Updated photometric figures to allow more accurate interpretation, and replace with minimum peak intensity and optical power requirements. The 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 the minimum accepted flash rate of 60 flashes per second to obtain the Cd-S/Min values. Removed ASTM publication contact information. Various editorial changes were made to harmonize the language used in other Warning Lamp and Devices Recommended Practices. Specified at which point the voltage from the power source is to be measured as a distance from where the wire exits device being tested to provide consistency in test setup. Removed test equipment quidelines – these are specified in SAE J1330. Changed photometer sensor distance from 3m to 18m minimum distance from device to harmonize with other warning lighting devices test requirements. Removed reference to instantaneous intensity must exceed 60% of values given for alternate method for a minimum of 50mS. Now uses optical power and peak intensity to determine intensity requirements. Added SAE J2139 for environmental testing for vehicles wider than 2032mm. The typical application for these devices is for school buses which are typically over 2032mm in width. 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. This also harmonizes with ECE Regulation 65, J595 and J845. Removed reference to SAE J1690. The SAE J1690 document assumes the flasher is external to the light and does not address if the flashers are integral to the light. This document has not been updated since 1996, and has not kept pace with many lightheads now incorporating internal flash circuitry. Since the J887 document now details the flash requirements, this reference has been removed. Removed reference to ASTM E 308-85. Color is specified by SAE J578. 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 of peak intensity also is readily done with current technology. 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. This will also harmonize with other warning recommended practices. Remove Alternate method since new method is technology independent and measures peak intensity and optical power. Added photometric stability requirement. Removed reference to SAE J1054. the document was cancelled in 1999.