Dual intensity LED

[geistc]

I am looking to build my own LED tail lights for my car. I have two questions:

First, where can I get dual intensity LEDs. I see a lot of new cars that have LED tail lights that illuminate at one light level for running lights, and then when the brake is applied, they go to a higher light level.

Second, I need to know how to power the LEDs from the 12volt power from the vehicle. I have not worked with electronics since high school so I have forgotten much of what I knew back in the old days. I am guessing that I would need to hook a certain number of LEDs in series to get the voltage at each LED to the correct level and a resistor to get the current to the correct level.

Any help would be greatly appreciated. Thanks

[frhrwa]

www.superbrightleds.com

[haklesup]

I don't think there are any Dual brightness LEDs. More likely an array of LEDs is either partially/fully lit or some LEDs are biased at two different currents.

Since cars are wired for incandescent bulbs with two filiments, I would assume any LED replacement would also. So expect an array of LEDs where some are lit with the parking lamps and all are lit with the brakes.

Biasing LEDs is mainly a matter of putting 3 to 5 in series with a resistor. The value of the resistor is a function of the amount of current you want to go through them all after adding up the voltage drops across each.

[Bob Scott]

I am looking to build my own LED tail lights for my car.
...................
I see a lot of new cars that have LED tail lights

I see a lot of cars, truck and buses running LED tail lights with burned out segments. I think I'll pass on this new trend until the LED makers get their act together to add dependability.

That, and aftermarket tail lights are not actually legal in some localities. Usually not enforced by state/provincial police but local police in random municipalities. My son is running a GTI with a European body and lighting. It looks stock, so they leave him alone.

Try running neon lights under your rice rocket up here and see how far you get without being stopped.

[Bigglez]

Greetings,

First, where can I get dual intensity LEDs. I see a lot of new cars that have LED tail lights that illuminate at one light level for running lights, and then when the brake is applied, they go to a higher light level.

The same LEDs are used for both functions, but the
duty-cycle of the drive signal is changed to change
the apparent brightness. GM Cadilac was first to market
with LED tail lights, and if you see one and purposely
scan you eyes while watching the tail lights you will
see multiple images of the LEDs, due to the relatively
low refresh frequency. Other vendors seem to have got
past this problem with much higher frequency control.

Second, I need to know how to power the LEDs from the 12volt power from the vehicle.

This is a tougher question to answer. The electrical
system in a car is fairly bad, in that the voltages
fluctuate and some electrical loads generate spikes
and other noise into the electrical system.

A further issue is that most cars use an electromechanical
flasher for the turn signals and hazard (four-way) lights.
These require the correct load (in amps) to operate.
When a trailer is wired to the car the flasher is often
replaced with a different rating to power the trailer bulbs.
Some flashers will no longer flash if one or more bulbs are
burned out.

Why are going to use LEDs? Perhaps you have a solid
reason that won't affect the way your new lamps
work with your OEM car wiring and flasher?

Comments Welcome!

[Bigglez]

I see a lot of cars, truck and buses running LED tail lights with burned out segments. I think I'll pass on this new trend until the LED makers get their act together to add dependability.

Similar story with LED traffic lights (signals). The local
municipal signals were changed over to LEDs in the mid
1990s, with grant money from the state electricity utility.
After all, an LED cluster draws only 11W compared with an
69W (special 8000hr) filament bulb!

Problem is that a high percentage (by semiconductor
industry standards) of LED clusters have failed. The
partial failures haven't been replaced in many cases
and show various failure modes (missing segments,
flicker, and "half bright" patches).

Comments Welcome!

[philba]

if you see one and purposely
scan you eyes while watching the tail lights you will
see multiple images of the LEDs, due to the relatively
low refresh frequency. Other vendors seem to have got
past this problem with much higher frequency control.

I've been noticing this a lot but must be more sensitive to this as even the higher frequency ones are obvious with the visual scan. The Caddy's are really bad - to the point of annoying. My wife is getting tired of my "lousy Cadillac engineers" grumbling when we drive somewhere. lol.

[L. Daniel Rosa]

Not nust cadillac. I see it on bmw and volkswagen. I think I saw LED lights on a lincoln, judging from the way it lit up but I didn't see it flicker.

What's with this lousy engineering anyways? How hard is it to feed the array with DC? Maybe the bean counters pulling out unnecessary components are causing the burned out segments too.

[geistc]

More info:

Bigglez wrote:

This is a tougher question to answer. The electrical system in a car is fairly bad, in that the voltages fluctuate and some electrical loads generate spikes and other noise into the electrical system.

I kinda thought that this would be an issue and have been thinking of building a separate regulated power supply to run all the LEDs.

Bigglez wrote:

A further issue is that most cars use an electromechanical flasher for the turn signals and hazard (four-way) lights.

I should have mentioned this earlier, but all the LED lights will be controlled by a microprocessor, such as a BASIC Stamp, so I will be no longer have standard turn signal flashers. This is also so I can do some custom effects such as scanning the third brake light in the direction of the turn signals and such. I am working on an '85 Camaro Z28 which I am rebuilding from the ground up so I am replacing the entire wiring harness. These cars have large rear tail light assemblies so I will be able to put in a good amount of LEDs to be able to some interesting effects.

[haklesup]

How hard is it to feed the array with DC?

The primary DC source in a car is very noisy, it can vary from 10V to 14V at any time and has lots of transient noise.

An LED's brightness can vary considerably under these conditions and its lifetime can suffer as well. Passively biasing an array of LEDs will work but it is not the best way to do it. PWM brightness control is more stable (despite the flickering some people observe) and results in longer device life due to less heat generated overall.

I'm not sure if the LEDs have the electronics in the reflector housing but I think it would be in the lamp base.

Incandescent bulbs are virtually immune to transient noise and their brightness varies less in the operating voltage range than LEDs

LED brakelights don't bug me. Its those very blue HID headlights I dislike.

I wonder what is the impetus to change to LED in cars. I suppose in some models it's just style but would the lower power consumption actually result in measureably better mileage or do they last longer or have better visibility.

I'm sure you can stuff a bunch of T1 base high brightness LEDs in a space with some resistors and make your own brake lights but it will cost way more than a replacement bulb and not work as well as a commercially tested design

[Bigglez]

Greetings (What's your first name?),

The electrical system in a car is fairly bad, in that the voltages fluctuate and some electrical loads generate spikes and other noise into the electrical system.

I kinda thought that this would be an issue and have been thinking of building a separate regulated power supply to run all the LEDs.

That would work, but remember that cranking a cold engine
can drop the battery voltage down quite a bit (8-9V) so a
linear regulator for your five volt rail will suffer. There are
low-drop-out (LDO) regulators aimed at the automotive market.
Why would you care? If you crank the engine and it resets
or corrupts your uC code you may have no lights!

You can run the LEDs from the battery without a regulator
if they have a PWM controller. The analog part of the
circuit would use local feedback to regulate the current
in the LEDs, thus avoiding the noise and flicker that
Hacklesup mentioned.

One thing you can safely assume is that vehicle
manufacturers have squeezed every component and
penny out of a design for high volume.

As Cadillac were first to market they may have been
constrained by technology and ended up with lower
frequency PWM than later designs can use.

A trip to a parts yard might turn up some late model
LED light clusters that you can reverse engineer and
save time and effort for your own projects.

A further issue is that most cars use an electromechanical flasher for the turn signals and hazard (four-way) lights.

I should have mentioned this earlier, but all the LED lights will be controlled by a microprocessor, such as a BASIC Stamp, so I will be no longer have standard turn signal flashers.

That would be kewl, but keep in mind that vehicle manufacturers
must meet government regulations, which includes an audible
flasher sounder (the electromechanical flasher "clicks") and
lamps must meet standards for brightness and colour.

This is also so I can do some custom effects such as scanning the third brake light in the direction of the turn signals and such. I am working on an '85 Camaro Z28 which I am rebuilding from the ground up so I am replacing the entire wiring harness. These cars have large rear tail light assemblies so I will be able to put in a good amount of LEDs to be able to some interesting effects.

That would be very tempting... Some local laws prohibit
aftermarket lighting effects, such as under chassis neon,
"blue" brakelights, etc. So your system will need a "kill
switch" in case you're noticed by the authorities.

Comments Welcome!

[haklesup]

SInce your building from the ground up and are not retrofitting the wire harness, I suggest you look into "LED Driver IC" chips (search that term"")

Also don't forget to look for application notes and reference designs.

There are many devices in this category. Devices that control the brightness with PWM are common and many can drive multiple LEDs (displays are probably beyond what you want but it goes that far)

Here is one of many that might proove useful to you
http://www.semtech.com/products/power_m ... ers/sc441/

Or a simpler one
http://www.madeinchina.com/1693967/P232 ... r-IC.shtml

[dacflyer]

leds are not so complicated, i made a set of trailer lights , all i used was
resistors and blocking dioads, been using them for many years now, and they are very bright too.

bigglez >> you said... Similar story with LED traffic lights (signals). The local
municipal signals were changed over to LEDs in the mid
1990s, with grant money from the state electricity utility.
After all, an LED cluster draws only 11W compared with an
69W (special 8000hr) filament bulb!

Problem is that a high percentage (by semiconductor
industry standards) of LED clusters have failed. The
partial failures haven't been replaced in many cases
and show various failure modes (missing segments,
flicker, and "half bright" patches).

i work in the traffic signal industry, your right, a lot of them leds are failing a lot with leds flickering or strings out etc.
the problem from that is, they are overdriving the leds.
typically 25 - 30Ma. LEOTEK and COOPERLED are the worst.
also DIALITE had some bad ones for a while, but now dial light is using a led engine in their leds. they are more uniform and look like a typical lightbulb signal, the led engine is in the back of the modual , and a freznel lens covers that, and then a colored outter lexan lens that mimics a traditional glass lens.


Here we never have used any 69 watt lamps ever..
smallest lamps we still use are 116 watt, used inthe smaller ped signals and the 8" signal heads. in the large ped signals and 12" signals we used 169 watt lamps, these are also 8kHr lamps, they have very hearty filiments, they give off way more heat than they do light. makes for a great heat lamp
altho we do not use any lamps in any signal heads anymore, except for a signal head that has 8" arrows ( there are no 8" led arrow moduals yet )
if there is any, they are not DOT approved yet.
and we are quickly getting away from lamps in ped signals.
we have been going to the led HAND MAN countdown ped moduals, they are cool. would love to see the animated ones here, like thay have in Japan..


{:>D

[Overlord]

I am looking to build my own LED tail lights for my car. I have two questions:

First, where can I get dual intensity LEDs. I see a lot of new cars that have LED tail lights that illuminate at one light level for running lights, and then when the brake is applied, they go to a higher light level.

Second, I need to know how to power the LEDs from the 12volt power from the vehicle. I have not worked with electronics since high school so I have forgotten much of what I knew back in the old days. I am guessing that I would need to hook a certain number of LEDs in series to get the voltage at each LED to the correct level and a resistor to get the current to the correct level.

Any help would be greatly appreciated. Thanks

The LEDs can be controlled by an electronic flasher as opposed to the older thermally controlled ones. You'll see those flashing LED turn signals that don't look right. The LEDs often don't provide enough current draw to run the older flashers right. There are aftermarket modules that will provide more current draw to make the flasher timing work.
I put in a module to sequence my turn/brake/flasher lights in a '99 TA. I had to replace the 3rd (outer) 2 wire driving light with a 3 wire light to include it in the sequenced flashing. I put in a HD electronic flasher. I could have replaced the lights with LEDs and it would have still worked well as the front filament bulbs provided enough current draw.

Here is a link to a guy that replaced his rear lights with cheap LEDs $9.95@Harbor Freight);
http://forums.corvetteforum.com/showthr ... ?t=1937973

Of course some premanufactured LED tail lights have MANY more LEDs;
http://cgi.ebay.com/ebaymotors/Red-Roun ... 0211167573

Now if you REALLY wanted to do some sharp LED lights, and have the tech knowhow, you could try something like this;
http://www.schlafer.com/corvette/lights.wmv

BTW, with my sequenced flashers; 6 lights flashing from the inside to the outer edge of the car, if I pulled over and turned on the flashers, everyone slowed down as they went by.