Basically I want to be able to have two blue (or white) LEDs on two small disks that will fit inside the eye spaces of a sleep mask I am making. These two disks will connect to an audio source so that they can flash in time to the music and in brightness based on the volume. The audio cable will need to be 6' in length with a standard headphone jack on one end and the two LED disks connected to the other. If the power from the headphone jack is enough to power the LEDs that would be good. If not, then the LEDs will need their own power source. Finally, the LEDs will be placed near to my customers eyes. So it is important that there be no sharp edges.
One concern, obviously deals with locating LEDs in direct proximity to the human eye. It may be a good idea to measure the light intensity as a precaution against eye damage. Besides from the visible light, it may also be a good idea to run a few calculations on the radiometric output. Blue LEDs emit near the low end of the spectrum, so the human eye is less sensitive to this wavelength. Also note that white LEDs can emit over a wide range within the spectrum. For a better understanding of this concept, consider two other LED colors not related to your project. With a green and ultra violet LED, it is possible that the radiometric output from the UV LED can exceed that of the green LED, but the eye sees the green LED as brighter and the UV LED as barely on. This is why some wavelengths can be potentially dangerous, especially those within the UV range of the spectrum.
Weight will most likely be a concern for the sleep mask. The customer would not appreciate a vast assortment of electronics adding mass to their mask. Thus, the optimal design will consist of eye mounted LED boards which contain only the LEDs, and rely upon an external controller board for functionally. This board will contain the LED driver circuity, as well as the MP3 player interface circuity responsible for producing light and color patterns based on the audio signal.
The simplest audio controller for LEDs will rely on some basic linear circuit technology. The controller would consist of low, medium, and high frequency activated circuits, supplying power directly to the LED drivers. Such a construction would not permit as much flexibility as a digital audio controller. In this design, a micro controller is added between the filters and LEDs. This allows you to control the LEDs based on a predefined software routine, and of coarse the inputs from the audio line. Not only would this method provide a higher level of flexibility, but also the ability to update the software as needed. It is probable that the LED audio controller circuity will require its own independent power source, as relying on the MP3 player for power could get tricky. This may lead to additional issues as new versions of MP3 players are released, so the external power supply is a recommendation.