DIY LED tail lights

[Christ]

Originally Posted by captainslug

Those are resistor values for 1/4 watt resistors in 820 ohm, 330 ohm, and 270 ohm ratings.
More resistance = less power delivered

I'm not sure what the spec on the LEDs he used are. But should you want to double check his resistor choices you can use an LED calculator.
LED Resistor Calculator

Don't resistors convert electricity into heat?

Isn't that kinda defeating the purpose of the electricity savings from using LED's anyway?

Not being smart here, I'm genuinely asking.

Obviously there is still an economic advantage in never having to change the bulbs again, but damn, it's only a very small amount you're saving, and that's if you changed them ALL on scheduled intervals.

[Memorytwo]

oh wow i just saw the ducati one. ive seen that one before, but i didnt realize that it had dual intensity. its only 2 resistors or something for that entire array!

EDIT:i am personally doing it to get brighter lamps. I have seen my brake lights during the day, and theyre a bit dim compared to some of the newer cars.
i realize that resistors arent effective, but it would also be nice if you can save some electricity so the alternator doesnt have to work so hard.

[captainslug]

Originally Posted by Christ

Don't resistors convert electricity into heat?

Isn't that kinda defeating the purpose of the electricity savings from using LED's anyway?

Not being smart here, I'm genuinely asking.

Obviously there is still an economic advantage in never having to change the bulbs again, but damn, it's only a very small amount you're saving, and that's if you changed them ALL on scheduled intervals.

Yes resistors convert power into heat so that the resulting output is reduced.
How much power is consumed by resistors is dependent upon the layout of the circuit.

However LEDs are still MUCH more efficient at turning power used into usable light. That light output is also very controlled.
I'm currently working on replacing a 310 lumen incandescent bulb that consumes 18 watts with a 430 lumen high power LED that consumes only 8.5 watts (resistor included).

The more significant difference between the two is service life.

[Christ]

Originally Posted by captainslug

Yes resistors convert power into heat so that the resulting output is reduced.
How much power is consumed by resistors is dependent upon the layout of the circuit.

However LEDs are still MUCH more efficient at turning power used into usable light. That light output is also very controlled.
I'm currently working on replacing a 310 lumen incandescent bulb that consumes 18 watts with a 430 lumen high power LED that consumes only 8.5 watts (resistor included).

The more significant difference between the two is service life.

Using half the power to make more light is quite significant.. I wouldn't play it off, personally.
Thank you for clarifying.. I planned on making LED lights for home use. (Screw them in just like the fluorescent replacements.)

[Memorytwo]

what light is this for? and wow i didnt know they made LEDs up that high, i do know they make 5W luxeon leds, but i didnt realize they made 8.5W ones.

[captainslug]

The brightest LED Luxeon makes can output 540 lumens at 6.6W (provided you don't have to use a resistor). The resistor used to power the LED from a 12volt supply ends up consuming almost 2 watts.

[Christ]

Originally Posted by captainslug

The brightest LED Luxeon makes can output 540 lumens at 6.6W (provided you don't have to use a resistor). The resistor used to power the LED from a 12volt supply ends up consuming almost 2 watts.

Could you not use two LED circuits to break the 12v down to 6 and 6?

I can't remember which type of circuit you'd use... I think you'd use two series circuits in parallel.

+[-|-|-|-|-|-]-
+[-|-|-|-|-|-]-


+ = input
- = output
[-|... = LED's in series


Something like that.. but it's probably wrong.

[captainslug]

No. The Luxeon High-power LED operates at 9.45 volts and consumes up to 700mA.
Endor Rebel - Cool White, Tri-Emitter, 435 Lumens @ 700mA [7007-PWC-08-3]

You can wire regular LEDs in series sets in order to reduce the power wasted by resistors. The further you do that the more the array loses the ability to handle voltage drift. Something that's kind of important when you're powering them from a battery.

[Memorytwo]

what?

[Christ]

So basically, you'd have to ensure a stable 12v signal to the input in order to run enough LED's to not use resistors at all...