Screen brightness issue too low on lenovo flex 15

Hello,

I recently bought a Lenovo Flex 15 touchscreen laptop running Windows 8, but I'm having a small issue: the screen brightness is way too low; it’s really very dark whether on battery or plugged in. At first, I thought it was the battery power management mode that was the problem, so I went into the settings for the different modes, and even in high-performance mode with the brightness setting at maximum, it doesn’t change anything. I also tried the traditional key combination that now exists on all laptops, which on mine is fn + f11 or fn + f12, but nothing works when it's at maximum. Lowering it does work, but of course, that's worse :(.

One thing I forgot to mention is that the laptop is equipped with a brightness sensor that is supposed to adjust depending on the lighting in the room I'm in. However, I can't figure out how to disable this feature, if it’s indeed the source of the problem.

I did find a solution to get a decent brightness level by switching to "Stable" mode in power management, but it states that this mode prevents the computer from going into sleep mode, so that might not be a viable option. Ideally, I should be able to achieve proper brightness in the other power management modes.

I hope I have explained the problem I'm currently facing clearly and that someone can provide me with guidance because I'm stuck now. Thank you in advance for your responses.
Have a good evening :)
Configuration: Windows / Firefox 26.0