For technical riding it will be virtually impossible to pick up a bright light that will last 12 hours.
State of the art (to my knowledge) are the HID (high intensity discharge) lights - much more efficient than traditional lights, but also much more expensive. They are far brighter than traditional lights.
While I haven't used one myself (yet), I will be buying one from Lume Lighting - www.lumelighting.com - but they don't come cheap. They are not too heavy, very bright, and have a claimed burn time of 3.5hr. Price is around the $300 mark (one of the cheaper HID lights) (handlebar or helmet mount)
I currently use a twin halogen (10W + 15W) from Cateye for technical night-time riding, but find that I still have to dismount for some difficult and unfamiliar sections that I would have been able to ride in daylight. I like this light, but it is not as bright as HID, and has a shorter battery life (on the single 10W bulb only, max of around 2hr? Both bulbs comes down to around the 1hr mark) (handlebar only)
However, for 12 hours you will need a second light, eg a small LED headlight for non-technical sections. If battery life is critical, do not use your main headlight unless it is a technical section. Pretty much any LED headlight will last 12 hours.
If the course is generally non-technical, then I would go with LED for the battery life and weight savings. I have used a range of LED lights, by far the best I have used is the Cateye HL-EL500
http://www.cateye.com/en/products/viewProduct.php?modelId=17&catId=7&subCatId=2
This probably comes in at around $50 (I'm in Japan so don't know for sure), and battery life will not be an issue. I have considered for long night rides using 2 of these mounted on the handlebars, and this is sufficient light for non-technical riding (I have used one only on a rough but non-technical ascent & descent, great for the ascent, ok but a little scary at times on the descent)