Replacing LED's in taillight

As far as I understand, LED brightness is determined mostly by the current. LEDs usually are wired into a circuit that limits current (most primitively, in series with a resistor, like I did on my trailer). So if you replace old LEDs that were supplied with little current, with new LEDs, the new ones are not going to get any more current and so they would not be brighter. You need to get more current for them. I would vote for buying a different light assembly.
i

I would vote for the right group. I bet this question has been asked a zillion times in the electronics group and chances are high to find it in an FAQ.
Nick

Not exactly. For a given LED, more current gets you more light, up to the point where it gets you a dead LED.
For two different LEDs, the same current gets you vastly different amounts of light, if the LEDs are vastly different, which they certainly can be, by several orders of magnitude. Browse through an electronics catalog website and read the numbers.
Conveniently for brake lights, bright red LEDs are fairly cheap. Yellow's not bad either if you want them for turn signals.
Flashing is a driver circuit (the current provider) issue, though there are some cheesy self-flashing LEDs on the market - but they won't be the really bright ones.

From what I remember of riding a motorcycle the jerks will look right at you and attempt to squash you anyway. They will then say something like Oh my god I didn't see you. Eternal vigilance is in order when on a bike.
Rather than reinvent the wheel, go to a truck stop and look at the standard offerings they have for LED tail light replacements. This is going to be a whole lot cheaper than buying the components and building the units yourself.
There are many variations on the theme and it would be an easy thing to retrofit the motorcycle to accept the standard offerings for the trucks and in the event of failure or damage it would be fast cheap and easy to replace the lamps.
The ones I have seen come in both configuations. The standard one is wired like a regular two filiment bulb. One common ground and two hot leads. When the tail lamps are on about 2/5 of the LEDs are ilumated, and when you hit the brake the others light as well.
They also sell these in marker lamp configurations, and one of these will probably serve well for your turn signals.
I would avoid strobe blinkers. Some police cars are equipped with them and personally I find that they are too bright and tend to cause a reduction in my night vision and depth perception when I come upon them at night. It is hard enough to see what needs to be seen without compounding the problem.

If you're really up for a DIY project, VERY bright LED's are available from Luxeon and Cree. At max brightness some of them would be hazardous (blinding) as brakelights. The red-orange 3-watt Luxeon III can produce 190 lumens at full rated current. By comparison, many of the xenon tactical rail lights used by SWAT teams produce 80 to 100 lumens.
A single 1-watt red Luxeon with a diffusing lens is about equivalent in brightness to the brake & turn light using an 1157 bulb on my Chevy truck.
Brighness of a given LED is more or less proportional to drive current. Different LED's can take different amounts of current. The usual "gumdrop" LED's can typically take 20 to 50 mA, while the Luxeon III can take 1400 mA. LED's do vary in efficiency, some being brighter than others for the same current. The viewing angle also strongly affects brightness; a narrow angle LED will look much brighter to those "in the beam", but considerably less bright elsewhere. I think a wide-angle would be best for brakelights.
The easiest DIY project would be a number and assembly of gumdrop high-brightness LED's. That's what is used on nearly all truck and trailer LED brake/taillights. A google search on LED will find a number of sources for them.
LED's can be made bi-level just by changing the drive current. They can be flashed, either on and off or bright and less-bright.

See they found one somewhat brighter than an 1157 bulb. Most of the other stuff on the market is not as bright as the OEM bulb it is supposed to replace.
Randy

Never going to happen. I sailed for years on a 16ft. Hobi Cat, brilliant yellow hulls 16' long with Tequila Sunrise sails. It could be seen at midnight on a foggy night at 3 miles..and have had countless near misses from power boaters who claimed.."they didnt see me"
Gunner
This Message is guaranteed environmentally friendly Manufactured with 10% post consumer ASCII Meets all EPA regulations for clean air Using only naturally occuring fibers Use the Message with confidance. (Some settling may occure in transit.) (Best if Used before May 13, 2009)

If I heard screaching tires, I would accellerate out of there fast! But to answer your question, the usual brake/driving light led bulbs use several leds arranged in a circular pattern and only 1/2 are used when you turn on your normal driving lights, the others are turned on as you press the brake pedal. So there are 3 contacts just like on an incandescent dual filament bulb, and in fact some are direct replacements. Light modulators, which flash your brake light can be purchased from vendors such as J&P cycles. In my experience the led lights work well at night but are a little weak in daylight. If you find a way to convert them to Luxon 3 watters i'd like to know about it.
cheers T.Alan

To add to the LED collective, note that replacement-bulb solutions will be much less effective at angles other than directly to the rear.
I'd like a curved LED brake light panel, myself, for dual-sport use.
Dave

These guys have a lot of what's currently available: shipping. They've got both individual parts and modules as well as bayonet replacements. I've used some of them for dashboard bulb replacements, those work well.
Stan

On Wed, 30 May 2007 17:44:50 GMT, with neither quill nor qualm, Gunner quickly quoth:
Let's hope you never heard screeching tires out there, Gunner.
Yeah, people just don't pay attention to what they're doing, and it gets worse on the road every year and with every trend (like cell phones, GPS, and portable video players.)
- Metaphors Be With You -

After a Computer crash and the demise of civilization, it was learned Gunner wrote on Wed, 30 May 2007 17:44:50 GMT in rec.crafts.metalworking : Autocannon.
Oh, that's right, you're in the People's Republic, you don't have any such problems which would necessitate making a response without first contacting the local authorities.
-- pyotr filipivich "Quemadmoeum gladuis neminem occidit, occidentis telum est. " Lucius Annaeus Seneca, circa 45 AD (A sword is never a killer, it is a tool in the killer's hands.)