question about the brake light

[sessem13]

as u read the rule about brake light, it says that it must be of minimum 15 watts !!
does this mean a 15 watts I/P electric power to be dissipated by LEDs ?? or it means the illumination power produced by the LEDs ??
u know also that LEDs illumination is measured by "mcd" or "lumens" & not in watts !!!
I ask this because I wonder why it is ruled to have such high power to dissipate while we should decrease the dessipated power as possible as we can !!
thanks in advance
Osama Kamal
Electronics Team member in CURT team

[sessem13]

as u read the rule about brake light, it says that it must be of minimum 15 watts !!
does this mean a 15 watts I/P electric power to be dissipated by LEDs ?? or it means the illumination power produced by the LEDs ??
u know also that LEDs illumination is measured by "mcd" or "lumens" & not in watts !!!
I ask this because I wonder why it is ruled to have such high power to dissipate while we should decrease the dessipated power as possible as we can !!
thanks in advance
Osama Kamal
Electronics Team member in CURT team

[rmk36]

As long as it is clearly visible in sunlight, you shouldn't have any problems.

[JWard]

I was worried about this too. I just about met the 15W power requirement, but the light was genuinely painful to look at (thank you insanely powerful LEDs) In the end we had to use diffuser paper to diffuse the light more evenly and so the perceived power by the user was certainly less than the 15W. I have seen some FSAE brake lights made up of a couple of the LED strips you can buy from maplin, which are about 2W IIRC. This is 20%-30% of the rule, but is still visible in broad daylight - so as long as you can see it, I doubt the scrutineers are going to analyse the LED's in there and check they meet regs.

The rule was likely written (and has remained unchanged) since the days when extremly inefficient bulbs were the defacto for brake lights

[sessem13]

so, u advice me just to use high bright LEDs whatever they achieve 15 Watt or not (I/P or O/P) ??
I hope u have any undoubted answer as the rule is very unclear !!
thanks

[acedeuce802]

Precisely. As long as the light is clearly visible in bright daylight, from a respectable distance, you shouldn't get any questioning about the acutal power output. That is what I took from the above discussion.

[mech5496]

15 Watts could be annoyingly bright for an LED light. Just check out on the linked video a "humble" 10W homebuilt LED taillight for a bike...

http://www.youtube.com/watch?v=dRB-6FokXw4

This thing is SO bright that IMHO is potentially dangerous... Now imagine something like that with 50% more power! I would love to go to a comp with a 15W LED light though, just to cause a rule change on the next release... :P

[JWard]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mech5496:
15 Watts could be annoyingly bright for an LED light. Just check out on the linked video a "humble" 10W homebuilt LED taillight for a bike...

http://www.youtube.com/watch?v=dRB-6FokXw4

This thing is SO bright that IMHO is potentially dangerous... Now imagine something like that with 50% more power! I would love to go to a comp with a 15W LED light though, just to cause a rule change on the next release... :P </div></BLOCKQUOTE>

Our Brake light was hidden in a mount for the diff, so some of the light wasn't visible. If you looked at it ~2m on an average day, you would have 6 green dots left on your eyes for an hour or so. I genuinely agree that 15W of raw efficient LED power is too much for an FSAE vehicle.

[TMichaels]

Hey guys,
the rule says:
B7.4.1
The car must be equipped with a red brake light of at least 15 watts, or equivalent, clearly visible from the rear. If an LED brake light is used, it must be clearly visible in very bright sunlight.

The key part here is or equivalent. You don't have to use 15W LEDs, just make sure that you achieve good visibility.

[wagemd]

Haha, I remember struggling with that rule years ago when that was my project. Anyway, I came up with some really... special... math to get a very rough equivalent lumen-&gt;mcd brightness. I don't have any of that work anymore, but you may be able to do something similar if you're worried about justifying it.

I ended up using 25 8000mcd LEDs and it could illuminate a medium size room. In the day. With the windows open.

I also saw pictures of a team who made a solid block of LEDs and their wiring guy had to wear a welding helmet to look at it...

Anyway, the point of all the ramble was that, as long as you use a few high quality, efficient LEDs, you should be fine.

[tedfennig]

LED's(light emitting diode) have 2 leads, one is an ANODE, the other is CATHODE. they operate at around 1.5-3 volts DC (direct current), but may vary depending on its rated voltage requirement. the wall outlet is 110 volts AC (alternating current), and from where LED Spotlight supplier (http://www.volunled.com/catalog/led-spotlight) i am(philippines), its 220 volts AC. first you have to convert the 220volts AC to DC, for that, there are available converters (opt for the converter that has many voltage settings) that are sold in stores. Secondly, it is how you connect the LED, 12v led lights (http://www.ledstrips8.com/led-light-bars-c-38.html) you can connect them in parallel, all 100 of them using a wire. LED's have a polarity, and will not lit if connected on reverse, which means that you will have to connect all the anodes all together in one wire connection and flexible led strips (http://www.ledstrips8.com/flexible-led-strip-lighting-c-32.html) cathodes all together in one wire. carefully solder them, and make sure that the 2 wire wont touch each other, or else it could get short circuit and will damage ur power converter, worst it could cause fire. after care fully checking and re checking all your connections, connect your power supply to each of the wires, set the voltage to the lowest setting(3V). and if the LED glows dimly, set it to the next higher voltage.

[Rex Chan]

This is what we use: MUR 2011 Rear LED Brake Light (~2W) (http://www.facebook.com/photo.php?fbid=10150400732188036&set=a.10150400731033036.361642.559588035&type=3)

Costs about $20 from LED Autolamps. Uses +12VDC and ~150mA (so ~2W). Bright enough to be seen in daylight across a kart track. IMO, people/teams who spend more than 10 minutes working on the brake light are wasting time: just go buy one and wire it up. We use brake pressure and the PDM, but how you trigger is up to you (we used to use switches, but since we already log brake pressure, it's a LOT more reliable to trigger it off that. And you can get fancy with different flashing rates depending on how hard the driver is braking).

[JWard]

Rex is spot on with his advice. Also, thanks for sharing where you found it. I may suggest this to our team in the future.