Warning: a very small percentage of people may experience a seizure when exposed to flashing lights or visual patterns. Even people who have no history of seizures or epilepsy may have an undiagnosed condition that can cause photosensitive epileptic seizures while using such a device. If you or any of your relatives have a history of seizures or epilepsy, it is recommended that you consult a doctor first.
For more than a decade now (e.g. Mitch Altman / Lady Ada*), hobbyists have the ability to build brainwave entrainment machines (also called called "brain machines" or "mind machines"). Let's build one too (and let's try and figure out what we're doing).