Topic: Making an led tail light(any electronics experts?)

[68grandprix]

I bought a circuit board and some red LEDs the other day because I wanted to make a really thin tail light to french into the rear edge of my solo seat. I soldered the LEDs in series into the board and tested it, but they are very dim. I tested a single one and it was the same brightness. Does anyone know the correct type of LED to use for a tailight? I had an LED tailight that I bought(it was like a trailer marker light) and that thing was really bright. The LEDs I got are 12volt, and the brightness is 1.5mcd(whatever that is, it's not very bright). Thanks, Jimmy

[SteveD CB500F]

There has been some discussion here about LED taillamps.  Modern bikes have them so why can't we make them work?

First question:  LEDs require current limiting, normally by a resistor.  You say they are "12V". If you buy an LED from Radioshack (or similar) and connect it across a 12V source with no resistor, it will shine very brightly (but not for long...)  So do these LEDs come with current limiting resistor?

Next:  If you connect them in series you are "sharing" the voltage between them and they will be dim. The more "sharing", the dimmer they will be.  If they have built-in current limiting, they should be connected in parallel.

cd = candela which is a measurement of brightness. One candela is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 × 10-12 Hz and whose radiant energy in that direction is 1/683 watt per steradian (that's told you!)

mcd = micro candela or Mega candela depending upon whether the "m" is lower or upper case.

I'll stop now before I enter the "he doesn't know what he's talking about" region...

[Tim.]

There has been some discussion here about LED taillamps.  Modern bikes have them so why can't we make them work?

First question:  LEDs require current limiting, normally by a resister.  You say they are "12V". If you buy an LED from Radioshack (or similar) and connect it across a 12V source with no resister, it will shine very brightly (but not for long...)  So do these LEDs come with current limiting resister?

Next:  If you connect them in series you are "sharing" the voltage between them and they will be dim. The more "sharing", the dimmer they will be.  If they have built-in current limiting, they should be connected in parallel.

cd = candela which is a measurement of brightness. One candela is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 × 10-12 Hz and whose radiant energy in that direction is 1/683 watt per steradian (that's told you!)

mcd = micro candela or Mega candela depending upon whether the "m" is lower or upper case.

I'll stop now before I enter the "he doesn't know what he's talking about" region...

You entered the "I don't know what he's talking about region" when you typed Resistor!

[Hondell]

Hi
Well actually there are 12v leds. They have a resistor built right into the substrate. If in fact you have 12v leds you can safely hook them up in parallel right up to your battery. What you are looking for though is a led with several THOUSAND millicandela.
Rick

[ProTeal55]

http://www.sohc4.us/forums/index.php?topic=10141.0

[ponch9]

i'd be glad to help. i am an electrical engineer....see this post
you really nee to figure out what you want first. ultra-brite led's like 8000-15000 work great....
http://www.ledshoppe.com/Product/led/LE1002.htm
the brighter the better....you can always use resistance to dim them.
the formula to figure out resistors needed go as follows:
(Vs-Vl)/I=R
voltage supply - voltage allowed (voltage min/max for the LED) divided by the mA for the led.
EX. 12v-3.2/.02=440 Ohms
*note the .02 is mA into amps first
for multiple led's (series only, parallel is not good as is using one resistor for multiple led's) you then add the voltages allowed for the LED's (which cannot be more than the Vs) then that becomes your Vl.
EX. 12v-3.2+3.2/.02=280 Ohms
any questions??? lol
http://www.sohc4.us/forums/index.php?topic=10141.0

[scout18]

Ponch how about a parts list and a how to for the rest of us. I can solder but I need a list of stuff to get to put a cool light together like th one you made for the original housing.

[68grandprix]

Today I went to Iowa Radio Supply, and the guy there was very knowledgeable. I bought some bright leds (only $2.55 for $10, radioshack ripped me off at $1.60 something a piece!) and two 120 ohm resistors. I soldered 12 LEDs in parallel and ran the resistors in parallel so when I hit the brakes with the run light on it halves the resistance. They are pretty bright, but the difference between running and braking isn't enough, so I will either mess with different resistors or order some superbrights for the brake light and use this one for running. Pics aren't great, but here they are, Jimmy.

[socalenduro]

I just ordered an LED  tail light, but i didnt ask if i needed a resistor or anything...
is there a way to tell with a volt meter?

[333]

If it is a 12 volt tail light, no resistor is needed.  And a volt meter will only tell you what you have on the vehicle, not what the LED needs.


And don't pull up a 3 year old thread for a fresh question.

[socalenduro]

yes SIR

[MJL]

If it is a 12 volt tail light, no resistor is needed.  And a volt meter will only tell you what you have on the vehicle, not what the LED needs.


And don't pull up a 3 year old thread for a fresh question.

I'm reading your post and looking at your avatar, 

[bradweingartner]

If it is a 12 volt tail light, no resistor is needed.  And a volt meter will only tell you what you have on the vehicle, not what the LED needs.


And don't pull up a 3 year old thread for a fresh question.

Why not? Is consolidation of related and relevant information really a bad thing?