Bgrigg, and all...
A rebuttal if you will, as I just want to set the record straight, and then I think we can let this thread die...(I'm guilty of starting it, I know...)
The ugly math is in the actual EDM, not the simple unit conversion from mph to fps then multiplying by time elapsed.
400ms is not 0.004s, but rather 0.4 seconds, which is definitely noticeable, and a big boon to most people's reaction times.
Every state I've been in has an interstate speed limit of at least 70mph. Most are more like 75-80mph. At 35 mph, the standard legal city/town speed limit, we are still looking at 20 feet of EXTRA stopping distance. If we were to start stopping at less than a car length from the 0-0 point (0 acceleration, 0 velocity, complete stop), no amount of improved reaction time would prevent an accident.
Also, multiple bulbs only keep working when wired in parallel. If they are wired in series, if one fails, they all fail. Unfortunately, wiring in parallel leads to a reduction in current per bulb, causing incandescent light bulbs to be (even) dimmer. This is not a factor with LEDs because they have such a low current draw.
I reiteriate: LEDs are substantially faster, and the reason they are used in automotive/street level applications is their ability to reduce accidents. My own engineering education and experience aside, here are a few more sources to hopefully settle this once and for all. I've tried to get purely scientific, governmental, or consumer level sources, first for unbiased information, and secondly for ease of understanding.
http://chemistry.beloit.edu/BlueLight/pages/hp/an1155-3.pdf (Fair warning, this one can get a bit hairy)
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=8026456&dopt=AbstractPlus
and finally, under the heading "THE TECH ADVANTAGES" at http://autospeed.com/cms/A_109124/article.html
The Tech Advantages High intensity LED brake lights have major advantages. When compared with incandescent lamps, their faster illumination time gives following cars significantly reduced stopping distances. Incandescent lamps used for automotive lighting have turn-on times in the range 100 - 300 milliseconds (ie up to one-third of a second). In comparison, a LED lamp has a turn-on time of 100 nano-seconds - pretty well instant! Those turn-on figures assume that full battery voltage is available, but voltage drops are often present in brake lights. If subjected to reduced voltage at the lamp, turn-on times for incandescent lamps are even longer. With a voltage drop of 4 volts, the turn-on time of an incandescent automotive bulb can as much as double. The brightness of brake lights is also greatly reduced if the lamp is subjected to this lower than design-level voltage. Studies have indicated that LED rear brake lights provide a braking response time advantage of between 170 and 200 milliseconds under favourable road conditions, and up to 300 milliseconds under adverse conditions. A 200 millisecond improvement in braking response is equivalent to a reduction in the stopping distance of 5.8 metres at a speed of 105 km/h. In addition, practical testing has indicated that the response time of a person viewing a LED brake light is actually faster than would be expected, even taking into account the shorter LED switch-on time. It's thought that a lamp that reaches full brilliance very quickly is more likely to catch the eye of the following driver than one that reaches full brightness only slowly. |
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Oh, and I'd have to agree that the main reason Tamiya went with LEDs was heat reduction. That's a good call, and something I overlooked, not having firsthand experience with the workbench. Thanks for reading along, postulating logical arguments, and above all, keeping this civil, after all, we're all friends.
My apologies to usmc1371, and you can have your thread back now.