For some reason in this discussion the thought of "dim" keeps reoccurring.
"NOTE: Light Emitting Diodes (LEDs) illuminate 200 milliseconds faster than incandescent bulbs For an automobile this means a faster braking distance response time, about a full car length of extra stopping distance at 65 MPH."
LED Stop Lamps Help Reduce the Number and Severity of Automobile Accidents Application Note 1155-3 NOTE: Light Emitting Diodes (LEDs) illuminate 200 milliseconds faster than incandescent bulbs For an automobile this means a faster braking distance response time, about a full car length of extra stopping distance at 65 MPH. Summary Another benefit of LED rear brake lamps is their significantly faster turn-on time than conventional incandescent signal lamps. This faster turn-on time provides a safety benefit to the vehicle following the vehicle using faster brake lights in situations requiring fast braking responses. The National Highway Traffic Safety Administration’s (NHTSA) 1996 Traffic Safety Facts estimates that 28% of all accidents are caused by one vehicle rear-ending another vehicle. This is the second largest cause of accidents (the largest cause being angled collisions between two vehicles at 36%). A recent article in Ward’s Auto World quotes Robert Schumacher, Delphi’s director of advanced engineering, as follows: “Our research shows that between 37% and 74% of rear-end collisions are preventable by early warning systems.... Just 0.5 seconds [500 ms] in early warning would reduce rear-end collisions by 60%.” Two UMTRI studies conclude that LED signals provide a braking response time advantage between 170 and 200 ms under favorable lighting conditions and up to 300 ms under adverse lighting conditions (e.g., viewing at a distance with high-intensity illumination on the lamp surface). Note that a 200 ms improvement in braking response time is equivalent to a 19.1 feet reduction in stopping distance at a speed of 65 MPH. In addition, the turn-on time for incandescent bulbs is adversely affected by reduced voltage at the signal light. A study by NHTSA of 546 large trucks showed that some trucks have such large voltage drops in the wiring that the voltage across the signal lamp is reduced to voltages in the range of 5.5 to 8.8 V. A study by UMTRI shows that at these reduced voltages, the turn-on times of incandescent bulbs can increase by as much as a factor of two. This means that braking response time of the following driver would be adversely affected by the response time of the truck’s stop lamp. In addition, the light output of the signal light can be reduced to 5% of the nominal value, which could cause the following driver to confuse the tail and stop signal functions. Thus, the use of LED brake lights for heavy trucks would provide an even larger safety benefit than for passenger vehicles. In addition to the benefits caused by the faster response time of LED brake lamps, another safety benefit is that emergency flashers using LED signal lights reduce the electrical current drain on the car battery. The expected electrical current required for LED signal lights is covered in detail in Application Note 1155-2, “Electrical Power Consumption Savings for LED Signal Lights.” Reduced electrical current usage increases the operating time of the flashers as well as reduces the likelihood of a dead battery. Studies by NHTSA indicate that the braking response time improvement for the use of incandescent bulb Center High2 Mount Stop Lamps (CHMSL) is in the range of 90 ms for light trucks and 110 ms for passenger vehicles. NHTSA has evaluated the long-term effectiveness of CHMSL for reducing accidents and concluded that they reduce the incidence of rear-end collisions by 4.33 per cent. At the time the study was done, almost all of the CHMSL on the road used incandescent bulb technology. The report concludes that if every car and light truck had a CHMSL that they would reduce property damage associated with motor vehicle crashes by $655 million per year. Another NHTSA report concluded that property damage only accounts for 35% to 24% of the complete economic costs due to motor vehicle crashes. Thus, the total economic cost saved by the use of incandescent bulb CHMSL is in the range of $1.87 billion to $2.73 billion per year. Considering that there are 192,213,000 registered vehicles during the year of the study, then the total economic cost saving for the use of incandescent bulb CHMSL is in the range of $9.73 to $14.19 per vehicle per year. If the average life of a motor vehicle is 10 years, then the total economic savings for the use of an incandescent bulb CHMSL is in the range of $97 to $141. The braking response time due to the use of LED signals is in the order of 200 to 300 ms for passenger vehicles, and even more for large trucks. NHTSA concluded that the braking response time for the use of incandescent bulb CHMSL is in the range of 90 to 110 ms. Therefore, it is reasonable to assume that the economic cost savings of LED rear brake lights and CHMSLs should be significantly larger in reducing the number and severity of motor vehicle crashes than the economic cost savings of incandescent bulb CHMSLs alone. Detail It is generally well known that LED technology has a significantly faster turn-on time than incandescent bulbs. Typical incandescent bulbs used for automotive signal lighting have turn-on times in the range of 100 to 300 ms.[1] In general, the turnon of LED lamps is less than 100 ns. Further, LED lamps don’t exhibit a high in-rush current, which might further delay the turn-on time. This faster turn-on time provides a safety benefit to the vehicle following the vehicle using faster brake lights in situations requiring fast braking responses. For example, at a speed of 65 miles per hour, a 200 ms faster braking response time from the driver in the following vehicle would reduce the minimum braking distance by: A number of incandescent bulbs were characterized to determine the turn-on time when driven with a fast rise time circuit. The basic circuit used a high current power supply (>17 A) supplying current to the bulb and power MOSFET switch. The power supply was set to 12.8 V. The power MOSFET had an on resistance of 0.1 ohm and switching speed of 50 ns. The bulb was mounted at the end of a #16 gauge 10 foot wire harness (20 feet supply and return) to simulate the effect of wire inductance that would be experienced in an automotive application. Typical results for one of the bulbs and an LED CHMSL array are shown in Figure 1. The summary of results is shown in Table 1. Distance traveled = (65 mph)(5280 feet/mile)(1/3600 hour/sec)(0
