around 2 Hours is from what i was told, depending on the temperature and how the light is mounted (upside down, or upside right). When its upside down, the heat can escape faster since heat rises, and it going through the fan. When its in normal position, the heat will gradually then get the light hotter and hotter. Basically when you have it upside down you can run the light up to 4 hours. But with it in normal position, 2 hours.
(my keyboard isn't workin right. grrrr)