I have one of these H4 LED bulbs in the headlight of my V50 Cafe.
H4 LED Headlight Rev2 - ADVmonster
I was able to replace the stock halogen bulb with only a small modification of the rubber cap to accommodate the LED bulb's heat sink. While the V50 is not yet ready for the road, I tested the LED headlight and it appears brilliant (literally). Very white light, high beam and low, seems considerably brighter than the halogen. The V50 has a traditional round headlight shell, mounted on "ears".
I am thinking of installing one of these in my 390. The key question is whether there will be enough room behind the LED bulb to allow for the heat sink, and whether the 390's headlight module will permit enough airflow to cool the bulb effectively. Also, in a series of demo photos, the vendor lists bikes that have been tested with the bulb. Among these is the 2014 KTM SuperDuke, listed in the "potential issues" category. The bulb apparently fits fine, but the fault light flashes because the SuperDuke's ECU thinks the headlight is burned out, due to the greatly reduced resistance vis-a-vis the halogen bulb. The fix is to install a resistor to simulate the stock bulb's resistance.
ADVmonster LED Headlight! - ADVrider
I am planning to try this mod on my 390 in the not-too-distant future, but first need to finish more pressing mods and also finish work on my Cafe. If it works, it will be a win-win: Better light for less current. Like the 390, my V50 has an alternator with marginal output- 260 watts. The LED bulb uses 20 watts on low beam, 25 on high beam, saving 35 watts versus the 55/60 watt halogen bulb. This is power that can go to heated grips, heated clothing or whatever. I think LED headlights undoubtedly will become the future standard.