January 05, 2005<br />
<br />
<br />
I've known that LEDs are faster to come up to brightness than Incandescent bulbs, but didn't realize how much different they really were.  Looking over a bunch of video, frame by frame (easiest method at hand right now), I see about 0.2 seconds faster, and really 0.3 seconds faster for the LEDs to hit full brightness.  The circuit used on the LEDs takes 0.0002 seconds to hit full brightness, from when the brake pedal is touched.<br />
<br />
So, lets say it takes 0.2 seconds.  Assume you are driving 60 mph on the highway.  There are 5,280 feet in a mile.  60 mph * 5,280 ft = 316,800 feet per hour.<br />
<br />
There are 60 minutes in an hour, 316,800 feet per hour / 60 minutes = 5,280 feet per minute.<br />
<br />
There are 60 seconds in a minute.  5280/60 = 88 feet per second.<br />
<br />
88 * 0.2 seconds = <FONT COLOR="#ff0000"><b>17.6 feet</b></FONT><br />
<br />
So, an LED brake light could allow a person to <b>stop 17.6 feet sooner</b> than with incandescent (normal filament lightbulb).<br />
<br />
But there is more.  I've noticed that folks react a lot quicker to the "instant on" effect of an LED vs. the slow ramp up in brightness of an incandescent.  What this equates to in reaction time is unknown to me. <i>(how many additional feet it buys you.)</i><br />
<br />
<br />
In any case, the 17 ft sooner the guy behind you stopped, that is plenty enough space to have completely munched your car, and then some.<br />
<br />
<br />
Here is a compressed video, sorry about the loss of frames and poor quality due to the compression, notice how the LED light, the top 3rd tail light comes on faster than the lower two normal incandescent tail lights:<br />
<br />
<a href="http://www.molalla.net/~leeper/dougta~6.avi" target="_blank">http://www.molalla.net/~leeper/dougta~6.avi</a><br />
 <br />
(I had to watch the video about 20 times to get my mind and eyes sync'd to actually appreciate it)
<br />
<br />
<br />
<i>[CPF-PhotonWrangler]<br />
<br />
Wow, thanks for doing the math!<br />
<br />
Yes, the LED's ramp-up is virtually instantenous, which is why they can use them in communications as well as video screens. It's possible to modulate the light REALLY fast.  [img]/ubbthreads/images/graemlins/smile.gif[/img]<br />
<br />
I've noticed that the on/off transition of LED tail-lights and traffic signals is much crisper looking and thus more attention-getting, which is definitely beneficial in terms of reaction time on the roads.  The highly monochromatic nature of LED light is also more noticeable against a background of visual clutter.  At least until all of the other lighted "clutter" is changed to LEDs also!</i>
<br />
<br />
Yes, you sure can, I've modulated Luxeons at 1/250,000,000 of a second.
<br />
<br />
<i>[CPF-MaxaBaker]<br />
<br />
Wow. 17.6 feet could definitely save some lives.</i>
<br />
<br />
Or save me from hospital bills, whiplash, or worse...
<br />
<br />

<br />
<br />
<i>[CPF-JamesS]<br />
For myself, I really like led brake lights. I don't like the PWM dimmed ones though,, I find them to be distracting as I look around and they leave the trail of flashes. There are some cars that are obviously current limited that really do look very nice.</i>
<br />
<br />
I more than hear you! I've been in some really bad situations (storms and heavy traffic) where the PWM'd tail lights have nearly caused me to over correct and caused a major accident.  I had to fight what my eyes were telling me to do...
<br />
<br />
<br />
In Reply to another comment- it's probably not legal just to go and modify your tail lights. <i>(check into applicable laws and regulations)</i>  One could add a third tail light, and aim it down.  That way they don't get blasted unless they are too close...thats definitely not safe though...<br />

<br />
In my tailight, I am utilizing 6 1W LEDs and a fast current regulator.  I was going to use some faster parts, but got to thinking, and 1/100,000th of a second time for comming up to full current regulated brightness is plenty fast enough.

Why six 1 Watters?  Originally it had 1 18 Watter, and this gives me nearly the same output or better as the original did, from all directions.
<br />
<br />
<br />
<i>[CPF-Darell]<br />
<br />
You got pictures of that 6-banger, Newb? I'm curious how you're sinking the heat, and how much room you have. I've been building LED third brake lights for a while now, and I'm still not happy with the design. I REALLY wanted a Lux5 in red, but that just didn't happen, officially.<br /></i>
<br />
<br />
I just used a large copper plate that covers the whole backside.
<br />
<br />
<br />
<br />
<i>[jtice]<br />
<br />
Your vid explains it well Jar,<br />
<br />
I agree, the LEDs are A LOT faster, and you are correct, the INSTANT on of LEDs catches your attention alot better than the ramp-up incans have.<br />
<br />
I am seeing alot of emergency, rigs, garbage trucks, etc using LED lights<br />
and I dont think its just cuz they dont burn out.<br />
I think they realize, or have been told that they are much faster.</i>
<br />
<br />
I just thought I'd mention, the tail light is still working great as we passed 2 years now.
<br />
<br />
<br />

<a href="http://www.molalla.net/~leeper/led.htm">Main site</a><br>
Mirror:<br>
<a href="http://jarhead.hobby-site.com/~jarhead/led.htm">Main site mirror</a><br>

<br>
<br>

<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
_uacct = "UA-2114182-1";
urchinTracker();
</script>