:welcome:
Sorry for the long post. This is just the tip of the iceberg, as you will discover if you have to custom design and build your own mod.
Firstly, there is lots of info buried in here back when Halogen lights were king. Googling this section will help. The main way to more light then was to overdrive the bulbs and accept shorter bulb life and need for a higher voltage battery with more capacity to maintain runtime.
That day has past. It would be money poorly spent IMHO to go that road now.
Secondly, while there are MR11 LED bulbs they run on 12 volt, and most are pretty wide beam and a quick googling showed no 6 volt. You could Google again. They would be direct plug ins if your housing is metal and can help keep the bulbs cool. BUT they use fairly inefficient LEDs and an inappropriate beam. If you can only get 12 volt ones you would need a new battery charger. Not a wise investment either, IMHO.
Thirdly, you have not stated your use of the lights (street, trail, both), your skill level to solder/build things, or a willingness to develop needed skills. If you are not mechanically inclined, for example, if changing a light bulb is a challenge, then I suggest you read about the Magicshine 808 here and forget modding these old lights. Or read one of the threads about flashlight options for bikes. Both choices are close to your budget.
Fourthly, LED's are the way to go IF you are going to mod your lights, but they produce a lot of heat so the light head needs to be aluminum (copper would work but I highly doubt they'd be copper). Steel doesn't spread the heat fast enough over the body of the light as a general rule, though with a single 3 W LED you might get by. Plastic light body? Forget it. You're done.
To make an LED light, you need a housing, and battery, which you have (they do have limited lifespans and yours won't likely have more than a couple of years left in it), one LED or more per housing, a circuit called a driver that can take 6 volts (as your budget won't cover a battery, too), and output the constant current the LED needs, an optic or reflector to shape a light beam, likely a cover glass or lens, and a way to get the heat from the engine to the light body. Many drivers include power levels and flashing modes.
There are a few 'light engines' that include the LED and the driver on a single cuircuit board. The ones from cutter with a single LED (
www.cutter.com.au) need more than 6 volts. These:
http://www.lux-rc.com/view.php?p=content/showcase/light_engines (top three) would work with your battery. Learning what the differences are among them will speed you on you way or tell you you don't have the LED bug.
You'd have to decide on an optic or reflector and the ones he has may or may not be the best for your needs. Reading here can help you decide or you can open another thread to discuss the issue.
You need to mount the light engine so the heat the LED and driver circuits produce is transfered to the housing efficiently. Hot LED put out less light, and can burn up. Rule of thumb is 1 sq inch of air-light interface per watt. These single LED units are about 3 watts, so the thermal issue isn't critical but must still be well done to keep the LED in the best temperature range.
If someone has modded these or similar lights and posts here with a blueprint, and you have the tools and skills to duplicate theirs, you are away. If not, and you now have the bug, Google here and read every term you don't understand. Read about other light projects to help see how to do yours. Technical terms Googled to Wikipedia helps as well.
I think you have to be a member to Google
here but you could wander through the threads on the older pages to see whether a similar light was modded.
Welcome aboard!
