If you wish to make by yourself a powerful lamp for your night bike rides, as some beautiful lights you can buy, the best choice in my opinion is to build it with a commercial LED lamp. Since some of these lamps work with 12V AC current, I decided to use as power source a 12V DC Li-po battery. The lamp has an included rectifier which converts current from AC to DC, so using a DC source works good here.

NOTE: I made this projects specifically to have a powerful lamp to mount for a night ride. All the connections, the meter, the lamp pins, the battery terminals, are NOT waterproof, neither water-resistant. For the same reason I don't need any power switch, and I need a fast to plug lamp support. Pay attention to use a so much powerful battery pack with rain or wet hands!

Step 1: The Lamp

Since commercial 12V LED lamps are now very common, you can find any number and type of them. There are lamps with a big number of standard white leds, with 3 or 4 or 5 more recent CREE leds, also with one single huge beautiful COB led.
I bought in a shop a 4 cree leds 6W lamp, but of course I can change it whenever I wish with a more strange or powerful LED spotlight. You can determine your best choice also referring to the beam angle. You can find an angle from about 30° to 60°, remember that a narrow beam will light further, but street sides will remain in darkness, the same as road signs.

Step 2: Power Source and Connections

The power source I chose is a powerful 5000 mAh Li-Po 3 cell 11.1 V battery pack. It's not handy because it need a proper charger, you can't store it with 100% of charge, you have to pay attention to not let it discharge more than a certain value, and you have to check your Li-Po battery packs every 6 months to ensure they have the right storage voltage. But, it's an awesome battery referring to weight and capacity!
You can buy a little cheap display which shows voltage and amperage (mine from HobbyKing.com), so to solve the discharging problem.
In the first picture you can see the cables I made to connect battery to the lamp, and you can insert the display between them if you wish.
To make the lamp plug I simply used a pair of electrical screw connections for wires, I sanded down the sides, so to glue them and obtain the right distance between holes. In this way I can tight the MR16 pins with the screws.

Step 3: The Stand

To make the stan I had an almost ready steel frame, which was probably for a bike reflector.
I decided to build a "fork" which holds the lamp from the two groove on the stem sides.
So, with the aid of a saw I cut an opening in its end, and I enlarged it with some files.

Step 4: A Bit of Work

I had to enlarge that opening to achieve the exact dimensions of the lamp grooves. Width of the opening has to be 9 mm and thickness of the plate has to be 2 mm. Because I couldn't reduce the thickness of the plate I gave them an edge, so that they fit into the grooves.

Step 5: That Fits!

Pushing the lamp inside the aperture, you'll notice that the connection is very tough and there is no danger the lamp falls out.
Some lamps have a glass or ceramic stem. In that case you have to pay much attention to make a perfect "fork" and to not break the stem.

Step 6: Fastening the Battery Pack

To see the display I decided to lock the battery over the horizontal pipe of the frame, where I already had a padding. If you don't have a padding, use some thick rubber. Li-Po battery packs have to be protected against collisions, so try to avoid open areas as the bottom of the oblique pipe. Li-Po cells can explode if struck, it's very dangerous!
I fastened everything with some velcro. Let some freedom to the white wire, so you can steer with no constrictions.
There is no power switch since the connections are very easy to unplug.

Step 7: Mounting the Lamp

When the front part of the light system is assembled, you can hang it on the bike fork, with the same bolt of the front fender.
I had to bend the support because my lamp was too low and the wheel shadow was annoying. The more you lift the light, the better you'll see in front of the wheel.
About the cost of the set it's not high at all (the lamp is about 15$, and the battery is an all purpose battery you probably already have if you like hobby-modeling). Of course we all know that nowadays you hardly save money making a tool or a gadget, but you could love the making more than the buying ;-)

Step 8: Let There Be Light

You can now connect everything and leave for your night-riding!
You have more than 10 hours of autonomy with a 5000 mAh battery! That's too much for me so I'm planning to add a second identical lamp and mount them side by side!

NOTE: I'm not sure the reason my lamp draws 350 mA from the battery, since the lamp details say 700 mA. It certainly derives on the fact the lamp is for AC current and I power it with DC current. But although I red some topics about the matter, I didn't understood enough to explain it here, I'm sure some of you can enlighten us ;-)