If you want to add some simple strips like on my copter above, then you don't even need to get your soldering iron out any more because Hobbyking now sell 200mm strips with JST connectors attached. Combine 4 of these with one of the JST-XH to JST power distribution lead and you can add LED lighting strips to your copter in a matter of minutes. One good tip if you want to light the whole arm up is to use some almost clear heatshrink tubing over the arms, which helps transmit the light all the way around the arm and has the added advantage of protecting the LEDs a bit and stops them getting knocked off.
The downside with this setup is that they only operate on 2s - 3s Lipo's and the power distribution cable is designed specifically for a 3s Lipo. If you do fly with a 4s or 5s Lipo you can always change the JST-XH connector to one that fits your Lipo and then just tap off 2 or 3 cells. The current draw of these LED strips shouldn't be enough to unbalance your pack that much, so I wouldn't worry about that when only tapping off a couple of cells from a 4/5 cell pack.
|9 mode Multi Colour/Function LED strip with controller|
If you want a more bespoke lighting setup than just a couple of strips of LEDs then you can also purchase much longer strips of LEDs by the roll, so you can wrap it all around your copter. The LED strips can be cut to the required length or soldered together to make even longer strips. Also available is fibre optic light strips that are really nice if you just want to highlight a particular part of the frame with more complex bend radii.
For the full UFO effect then you want some flashing, pulsating, colour changing lighting for your multicopter. Again, you can purchase a receiver controlled colour changing LED strip from HobbyKing which uses RGB LEDs to provide a changing colour spektrum which you can select using a spare channel on your transmitter. Flytron make some really good Strobon - combined navigation and strobe lights which are really bright and would look excellent on a multicopter.
The video below shows the Strobon light attached to a hunter v-tail frame from Dialfonzo.
On my builds, I like to use a receiver controlled switch to control my lights, so that I don't have to have them on all the time and it's fun to fly at night only switching them on and off every now and then. This adds a little bit of complexity to the installation, but is well worth the effort if you have a spare channel. It also always gets a smile from spectators when you take your copter up high and then start turning the lights on and off.
Here's a little video I made to show just how easy it is to add some lights to a multicopter. Apologies for not being the best film maker and my croaky voice, as I was suffering from a cold when I filmed this.