[Matt] wanted to increase the intensity of the center brake light on his car. The factory installed light uses a 20w incandescent bulb and although aftermarket LED replacements are available, he decided to take the retrofit on himself. Using the Fresnel lens from the light assembly as protoboard, he mounted a row of 10mm LEDs along with their current limiting resistors. He then broke the glass from the original bulb, removed the filament, and soldered directly to the two electrodes. This way the bulb socket can still be used to connect to the car’s electrical system.
heh… I made one out of a old Nintendo r.o.b. and mounted that to the rear deck in the car. of course, that car didn’t have a high mount brake light to begin with. I also wired directly from the brake light switch at the brake pedal and grounded it to the car near the mount.
http://www.myhomeintexas.us/media/pics/Cars/Pontiac-tail.jpg
Don’t have that car any more and haven’t gotten around to modifying my current ride yet, but I plan to *g*
Why does this not suprise me with the ever increasing brightness of car lights over the past few years, if the headlights don’t blind you the brakelights will!
haku:
He only wanted to increase the light output because he also wanted to tint the lens black and wanted the visible light to stay the same.
21Watt bulb power vs 0.9 watt LED?
21 * 3% eff = 0.6 watt worth of photons vs 0.27 watt worth of photons
Gotta love bright idea’s
(Assuming 3% efficiency for bulbs, and 30% efficiency for LED’s)
steven:
The LEDs are more directional, so you don’t have wasted photons that are absorbed by the reflector etc.
Also, less photons are released in the infrared range, the majority of them are released as visible light. Not so with an incandescent bulb.
@steven: photons aren’t measured in watts (well, actual photons are a different matter altogether). It has nothing to do with wattage, rather light intensity, ie lumens (or milli-candelas in the case of LED’s)
Also, no bulb to replace. Unless something goes catastrophically wrong, you’ll likely replace the car before you do the leds.
I’ve been wanting to do a few automotive LED projects… is the best way to still use a resistor per LED or is there a better circuit for driving large amounts of LEDs… particularly with a larger light where I’d want to swap in a 40-50 LEDs I’d think some kind of more advance driving circuit would be more appropriate.
also most cars that come with LED lighting from the factory use larger, brighter and I’m assuming more reliable LEDs (read: more resilient against vibrations, extreme temps, etc.) Any idea what the OEMs use and where I could get something similar?
I don’t understand the reason for this mod. Can someone tell me why he’s doing this?
—-but I did also want to tint the centre brake light.—but I prefer the blacked out look
He didn’t even post a shot of the light working.
I did this for a school electric car project in college. It had round brake lights, so I mounted high-intensity LEDs to a round PCB, busted the base off of a standard bulb, soldered the wires on, and epoxied it together. Drop-in replacement.
Oh, and P.S. about the photon energy, all that white light is filtered down to only red. That’s right, OYGBIV is all wasted, as well as a lot of IR. The LED releases light only in the part of the spectrum you need a brake light to do so: red. So, it’s brighter, even though it’s not releasing as much actual light energy. More light makes it to your eyes.
What about he Fresnel lens? The LEDS are facing away from it. Should we not assume that it was placed in the light assembly for a reason? Break lights are intentionally focused at driver level behind you. Removing the lens and adding more lumens is counterintuitive.
looks like crap to me!
OEM LEDS (still need a bunch of them):
(Philips) Lumileds Superflux
They take 70mA @ 3V
Next time, consider the red-orange snapled from Lumileds!:
http://projects.dimension-x.net/archives/219
Couldn’t he have wired the LEDs in series and saved a bunch of resistors?
As geep says –
using 1 resistor at 330 ohms per led is rediculous.
That light could easily run 5 or 6, 2 volt leds in series with one small resistor, or better, an led driver.
Efficiency in that system is CRAP, as its burning off 10 of the 12 volts. BS ‘efficient’.
Comment and question.
Doesn’t directly apply here, but many cars (Japanese) have buzzers to warn of blown brake lights so /LED\ retrofits need to waste current to stop these activating.
Q: can anyone supply a formula or rule of thumb that relates the wattage of the a replaced lamp to the candella /LED\ output for equal subjective brighness? TIA.
frollard, that is correct. he should at least put three LEDs per series so that it is more efficient. in that case when one led dies, the rest 6 should work great.
Isn’t this quite dangerous without the Fresnel lens properly installed over the LED’s?
A normal bulb would have a 360 deg. viewing angle, but LED’s are more likely to be something in the 50-60 range. As their all pointing straight-backwards and there appears to be no kind of lens in front of them if you are looking at the car at an angle you couldn’t see if the light was on or off.
As their all pointing straight-backwards and there appears to be no kind of lens in front of them if you are looking at the car at an angle you couldn’t see if the light was on or off.
good thing that they are only for the people driving directly behind you
Keep in mind that this is illegal in some countries! In Germany you need an “Allgemeine Betriebserlaubnis” or an “europäischen Typgenehmigung” (=type approval) for such parts.
There’s a basic misunderstanding here. The original lamp was at the focus of a *fresnel lens* (see Wiki) which redirected the divergent light towards the rear. A Fresnel lens is simply a compacted form of a conventional lens and produces the same result – it is beam-forming, *not* a disperser. So the original arrangement wasn’t designed to disperse the light to the sides.
With the change over to /LEDs\ (which contain their own lens) there is no longer a single source, so the fresnel lens has no use, but even if all the /LEDS\ were aligned to face backwards they still have a considerable beam width, likely to be greater than the original beam.
But they don’t have to be all aligned rearward – they can be splayed so they actually give a wider overall beam, and who is more interested in you stomping on the brakes – the driver directly behind, or someone entering from a side road?
After just completing a 5kkm road trip I found that the new /LED\ stop, tail and turn lights are not only brighter, they have greater dispersion than the old style.
It’s true that connecting the /LEDS\ in series groups with single resistor is more efficient, but it also makes them more sensitive to voltage variations. Since hackers aren’t worried about production expenses here is a constant current supply designed to overcome this problem in solar-powered houselighting;
http://www.ozvalveamps.elands.com/techsite/ledlight/ledlight.htm
I really appreciated the explanation of how electronic components work. I had not realised that it was the smoke inside the LED and makes it work. I’ve hooked up a few LEDs backwords over the years and accidentally let the smoke out. Now I understand understand how that works. Thanks!
@twistedsymphony:
Lets look at a standard Red LED with a voltage drop of 1.6 volts. When it is running near its maximum light output, it can get warm. Add environmental factors, and your LED’s can get over 85 degree C fairly easily. This causes your 1.6 volt LED to become a 1.3 volt LED. If you had 5 in series, your 8 volt drop becomes 6.5 volts and now your resistor is too small and your LED’s die. This is why larger LED systems should use a LED driver (aka constant current driver) instead of a voltage regulator.
I thought about doing this for a while when I had a VW Vanagon. Vanagons have rather dim brake lights, which is probably why almost every Vanagon you see on the road has been smacked in the rear.
It’s great and all, except automotive power isn’t guaranteed to be 11.5-14.6VDC. It can spike to 40VDC, which will pop these LEDs, due to having current limiting resistors instead of a constant current source regulator. For the hobbyist, no big deal, but it is something someone should consider.