Taking picture on a DSLR can be challenging to some as there are a number of settings that need to be taken in to account such as shutter speed, ISO and aperture all of which need to be balanced to get just the right amount of light to the sensor without making the shutter open so long that you get blurry images. Under or over exposed images are also too easy to create if settings are not correct for the environment around you.
A traditional way of working with this challenge is either by experience gained over a number of years, or by using an expensive light meter that can detect the light around you and provide the settings you need.
To lower the cost of light meters, one company is launching a device called Luxi that attaches to the front facing camera on your iPhone. It is compatible with the iPhone 4/4S and iPhone 5 and fits snugly over the camera. You then fire up an app and can find the best settings for the current lighting available.