Use Camera - to calculate Lux/Brightness?

Does anyone have an example of how I could use Titanium to produce a light sensor? I found LuxMeter on the Apple store, so I know someone has figured out how to do it in Objective-C. I assume I will need to track down a camera module which exposes at least:

NSDictionary* dict = (NSDictionary*) CMGetAttachment(sampleBuffer, kCGImagePropertyExifDictionary, NULL);

NSString* exp = [nsDict objectForKey:@"ExposureTime"];

Any assistance would be greatly appreciated!