On 3/2/06, Alan B. Pearce wrote: > >Wether the time difference is actualy reduces > >accidents I don't know, > > I have serious doubts that it does. After all a filament bulb is essentially > instant on anyway, it must take all of 100 mS to reach full brightness, and > fade again - apart from headlights that is where the fade of the glow is > easily seen in the dark. Having read about studies demonstrating it earlier, I'm fairly convinced. The following paper indicates that LEDs turn on as much as 200mS earlier than incandescent bulbs. A lot of the problem appears to be the large inrush current of the bulb coupled with the inductance of a long wire run to the brake switch and power source means that many bulbs take 200mS to turn on, while some take as long as 300mS. Few cars turned the bulbs on around 100mS. http://chemistry.beloit.edu/BlueLight/pages/hp/an1155-3.pdf Also look at the abundant resources in a Google search: http://www.google.com/search?q=study%20LED%20tail%20light%20reaction%20time Some indicate that the reaction time of the following driver is improved by at minimum 50mS, and generally 100mS - which is the real point. It doesn't matter how fast the lights get to 100%, or 80% - what matters is how fast the light is percieved by the driver behind. The following study goes through a range of drivers and a range of setups (center mounted leds and bulbs, normal right and left side tallight leds and bulbs, men and women of different ages, etc): http://www.visteon.com/utils/whitepapers/2002_01_0379.pdf Arguments against the LED improvement usually revolve around the closing reaction time - while a car going at 70mph may see the light 1 car length earlier, the fact the the car braking in front is also going 70mph means that the difference in speed while braking, or the closing time, is generally under 20mph. The difference in position, therefore, over 100 or even 200mS is not a full car length. So: 1) There is a significant, measurable difference in driver reaction time on the order of 50-150mS between incandescent and LED bulbs in a driving simulation. 2) The difference generally never means more than 1 car length difference in stopping distance, and less than a meter of difference considering relative vehicle speeds/positions 3) While studies with large trucks show a statistically significant reduced accident rate, that is largely due to 300mS or longer turn on times due to long wiring runs. LEDs are proven accident reducers in this area. The best option, I believe, to put this to rest is to study data from the national traffic accident database: http://www-fars.nhtsa.dot.gov/ and compare two similar cars with similar body style and demographics, one with LED tail lights and one with incandescents to see what exactly the difference is in accidents. As an aside, a good article on flashing brake lights mentions the difference between LEDs and incandescent bulbs: http://www.msnbc.msn.com/id/11351634/ It indicates that the NHTSA awarded an examption to a german car maker to allow 5,000 cars with flashing brake lights to be sold in the US to determine if they result in fewer accidents. I suspect that while there is a measurable decrease in accidents due to LEDs, flashing LEDs as described in the article will have a significantly greater impact. -Adam -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist