Although the light does seem bright when using the app, this perception is due mainly to the contrast to the dark - hence the importance of finding a dark space. The peak light intensity 7cm from your eyes is still only around a third of the brightness of a cloudy day and 1/20th that of direct sun, well within safe bounds, especially with eyes closed. We're trying to recruit an ophthalmologist to our Medical Advisory Board to give us leading research into this as well.
Though if at any point you do feel uncomfortable, it's best to stop the experience. Your comfort and wellbeing is our top priority.