iPhone brightness private API not working properly

I am trying to set the brightness of the backlight, but it's acting very strangely. I am using the private API:

[(id)[UIApplication sharedApplication] setBacklightLevel:1.0f];

However, when I call this, the screen dims, not becoming 100% bright like I thought it would. I have tested this with a variety of numbers, and here is what I got:

0.2: dark

0.3: light

0.4: dark

0.5: dark

0.6: light

0.7: dark

0.8: dark

0.9: dark

1.0: dark

1.1: dark

1.2: light

1.3: dark

1.4: dark

1.5: light

Some of the values were slightly brighter than the darkest values, but that is the overall trend. It d开发者_如何学Coesn't seem like the pattern makes any sense. Does anyone know what scale the brightness should be on?

The problem is that the compiler doesn't know a method takes a float unless you declare it. So the float you pass in is getting converted to another type when you pass it and then that new bit pattern being reinterpreted as a float by the method. You just need to have the method declared in a header that file knows about and the float will be passed unaltered.