These are the current details - but I am rebuilding it at the moment:
The light rig is 2 x 1 watt warm white LEDs:http://www.maplin.co.uk/1w-high-power-l
powered by a lithium ion rechargeable CR123 battery:http://www.amazon.co.uk/UniRoss-Sprint-
and a battery holder, some bits of wire and a couple of extra standoff fittings on the lower spreaders.
The whole lot weighs around 40 grams, with around 20 grams being concentrated at the base of the spine (battery & holder).
The amount and spread of light is good, making flying in complete darkness practical, and the extra weight doesn't seem to have too much of a detrimental effect.
Before the flight, I ran the rig to see how long the lights would run on a full charge of the battery - the lights lasted over 2 hours, so maybe a lighter lower capacity battery could be used.
There was an unplanned "battery ejection event" during the flight, which was quite surreal, as the kite just vanished in mid-air. Of course more work is needed on securing the battery and holder in place more securely - the current arrangement of double-sided velcro wrapped around the battery and holder and under the spine velcro doesn't grip enough.
More work is also needed on fixing the lights to the kite securely but allowing them to be easily removed - so far that's proving to be a lot trickier than it sounds.