LED Tail light Schem... correct?

[Integraoligist]

I'm creating my own tail lights for my car using these LEDs:
10mm Red
40,000 mcd
12 degree
(typical V and A i do not have yet, i will post as soon as i get them)

Side notes to this schem. During the day, the "Tail light" is not ON, so it reads 0V however when the brake is applied the "Brake light" will read 12V.
Night time, "Tail light" will be ON reading 12V and when the 12V "Brake light" is applied, both the Tail and Brake lights will be outputing 12V.

Does this schem. look correct? I did not add Voltage regulators because the resistors will be large enough to handle any Voltage "Spikes"

 

[Exo]

The leds are backwards.
Also, to increase efficiency, you can put groups of leds in series. How much of them depends on their forward voltage.

 

[audioguru]

You can do it like this if the forward voltage of the LEDs is 3V or more. If the forward voltage is only 2V then 3 LEDs can be in series.
You don't need a bunch of resistors in parallel to dim the tail-lights when a single resistor will do the same thing.

40,000 mcd is such a high brightness that the beam is probably focussed to an extremely narrow angle. You probably won't see the LEDs unless you are directly behind them. I think that vehicle lights should have a wide angle of visibility.

 

[Integraoligist]

the viewing angle of these 10mm LED's are 12 degrees (updated first post) and will be behind (butted up against) a 1/4" thick lens

the "usuall" for Semi-Truck LED Tail lights are 18 degrees at 8,000 MCD which is behind (butted up against) a 1/8" thick lens

I figure the thicker lens will make up for the 6 degree loss of viewing angle? thoughts?


Thank you for correcting the schem. any idea what size diodes I can use with this circuit?
(i'm still working on getting the info for the led's)

 

[audioguru]

12 degrees and even 18 degrees are very narrow angles. Cars have tail-lights that can be seen well at any angle. Maybe trucks use a cloudy or grooved lens that diffuses the beam. A clear coloured lens won't increase the angle of the beam.

A 1N4001 or 1N4002 diode is OK for 1A. Each string of LEDs is probably only 30mA. :lol:

 

[ThermalRunaway]

You can actually buy replacement bulbs which are LED lamps with a direct fitment for the original part can't you. Since they are obviously designed to be used behind a standard coloured lens (or standard clear lens) I wonder what sort of viewing angle they are? 18 degrees does sound a little too narrow...

Brian

 

[Integraoligist]

the truck LEDs are behind a Red lens which is not diffused...

the lens i have are thicker and ARE diffused so in theory they should produce more of a view on the lens.

Yes they do have 1157 LED bulbs, however they are not nearly as bright as incondecents... they have figured that it would take an arry of 500 LEDs to light up an entire assembly the way an incondect does. most of these leds have a 12 degree viwing angle as well and are around 7500 mcd.

Note that when you place these "drop-in" bulbs into a tail light assembly that the bulb is 3.5-5" away from the lens...
The tail lights im working on will have them butted against the lens so even a 7500 mcd 12 degree LED will show though it.

 

[Integraoligist]

would i be better off going with this:
https://www.electro-tech-online.com/custompdfs/2005/08/SSP-01TWB6UWB12.pdf

10mm Red LED

Typ.
12V
20mA
8000mcd
31 degree VA

Max
14V
20mA

A lot larger viewing angle and the same Typical MCD rating as most DOT Approved Semi-Truck tail lights.

Thoughts?

 

[zevon8]

I am not sure what lens you are using, but a huge part of the lamps effective pattern is generated by the lens design. The lens must also act as a reflector, unlit, with the appropriate viewing angle to meet FMVSS108.

I use LED lamps daily at work, and there are stringent guidelines and testing approvals that must be met for Stop/Tail/Turn lamps as well as what are classified as "Auxilliary lamps."

The lamps we use fall into these 2 categories, Auxilliary being 10 LED, and legal S/T/T being 24 LED for red, and 39 LED for Amber. Depending on the type, the viewing angle is different also.

"Angularity" as it is called in the industry, is one of the strictest guidlines to meet. The viewing cone listed in the spec sheet for LED's does not tell the full story. You need to consult the photometric charts for the device, and find out how the intensity at the given angle is reduced. The emmited light drops significantly as you move off-axis.

Long story short, It is almost impossible to "home-brew" a legal S/T/T lamp. Even using a factory incandescent lens and housing will not do the job, since it was designed for a lamp with a radiation pattern of approximately 270 degrees, or atleast 180 degrees.

 

[Integraoligist]

"and legal S/T/T being 24 LED for red"
Ah but i see many trucks that have the 10mm led's but only 6 of them. They are also "approved"

Thoughts?

 

[zevon8]

I know exactly which one you mention. They are one of the, ahem, shall we say lowest cost units. They use a fresnel type lense around each element, to give better dispersion. The biggest problem with these units is that often the failure of a single or if you are lucky, maybe 2 LED's will render the unit no longer serviceable for required output.

They are often used in multiples also, so a single US40 series lamp is often not the only lamp.

My customers rarely use them, except where they are strobed, and suffer higher mortality rates anyways. i have never been impressed with the angularity of these units either.

I still prefer ( as do my customers ) lighting that is as bright as allowed, since the idea of a signal lamp is to convey its message clearly, and safely.

My opinon, of course.

 

[Integraoligist]

I'll tell you, i've been planning on taking the round Semi-trailer LED Tails (the 25-40 led as you mentioned) and putting the LEDs/board behind my Lenses... however I'm only able to fit a maximum of 3" round in there...
all i've ever been able to find are 4" round (which has a 3.5" board)

other then them, and back to Incondecent bulbs, what other choice do i have?

They do have 2.5" Marker lights that i've found... and yet again, not Tail/Stop light.

Thoughts?

 

[zevon8]

I don't think you will find a lamp assembly under 4" that is bright enough, without going to a specialty lamp and driver circuit. I have seen some replacement modules for vehicles that include a new housing, but the selection is generaly limited to the most popular vehicles. I am thinking of vehicles like pick-ups, Crown Victorias, etc, the type of vehicle that gets used for emergency services. These modules are pretty pricy though. The ones sold in "custom car magazines" are variable in quality and some are downright questionable as to wether they meet spec.

For an idea of what's involved in designing a vehicle lamp module, take a look at the Lumiled design note here:

https://www.electro-tech-online.com/custompdfs/2005/08/AB20-1PDF.pdf

It contains great info on light output requirements, depending on the application.

 

[audioguru]

Hi Zevon,
That is a great article. Its detail shows why after-market replacement vehicle lighting assemblies are illegal in Canada, I guess because most of them don't meet the spec's. :lol:

EDIT:
The assemblies are illegal to use. They are legal to be sold and are everywhere. I've seen many school kids in their little Hondas with replacement lights that can hardly be seen. They haven't been caught yet.

 

[Integraoligist]

ok, so the next question would be... other then a regular white incondecent bulb (which makes a Pink tail light) what can I use that creates more of a Red output?

I've seen those Incondecents with a red "coating" over the bulb, but yet again the red filtersout the brightness of the bulb as well.

Thoughts?

 

[zevon8]

Thanks audioguru, that's the type of info I have been dealing with for the last couple of years. I have been to many meetings with government officials and engineers in hopes of getting some of these lamps approved for use as replacements for incandescent lamps in the work I do. LED technology is great in so many ways, and is finally becoming mainstream.

It drives me nuts when I see those clear lamp covers with lame little LED lamps on modified cars. That and people who put tinted covers over their tail lights. These lights are critical safety devices that have been carefully engineered for everyones benifit.

I install lighting on emergency vehicles, and trust me, when you are on the side of a highway at night in the rain, you want your vehicle to look like the mothership from Close Encounters, or things get ugly really fast.

Integraoligist, replacing lamps with LED's is very complicated, and not only risks getting a ticket for having non-standard lighting, it can be a safety hazard if not done correctly.

I have seen very few aftermarket replacement lamp assemblies for passenger vehicles where the manufacturer will have a DOT or FMVSS approval certificate. The ones that do are usually atleast twice the price of a factory replacement of the incandescent type. Vehicles that use the round US40, PAR36, hotdog US60, or similar lamps as found in trucks are a different story. Nearly all of these lamps have direct LED replacements that are legal, and due to the volume, very reasonable in price.

Other than the truck type direct replacement lamps, most of the other "arrays" used in passenger vehicles ( including factory OEM ) use a PWM controller to drive many surface mount chip LED's at very high levels with controlled pulse rates to produce high output. This is not easy to do, requires considerable engineering and cost. This is why generally these LED taillights are only standard equipment on the more high-end vehicles.

While I think doing a conversion of tail lights is fine for a non-road show car, I just don't think it is feasable for the average person to attempt, given the risks involved.

/ "rant" over, I will step down from the soapbox

 

[musthave]

Hi I just finish making a change to my third brake out of necessity my car is a 87 and cant get a replacment socket reflector conbination for that light
any way so I made a replacment LED here is some pics.
zevon8 great info you provided.**broken link removed****broken link removed**

 

[audioguru]

33 LEDs that are diffused by the lens grooves?

 

[Integraoligist]

ok ok, i'm gonna get these and try them out for the hell of it, just to see how bright i can actually get them as compared to an incondecent.

Thoughts on this circuit and the Values?

**broken link removed**

 

[audioguru]

Hi Int,
You have so many LEDs in series that there is a huge difference in their current between an 11V supply and a 14V supply.
Also, there is hardly any difference in current between tail lights and brake lights: