Flashing LED's variable speed. Circuit help appreciated.

Hi,

I would like to make a simple mind machine. 

It will have 6 red LED bulbs.

They flash concurrently and their frequency can be controlled by a variable resistor.

When the resistor is at its lowest setting they should flash at 1Hz, when it is at its highest setting it should be at 15Hz

The LED's need to be as bright as possible but also need to be less than a centimeter from a closed eyelid, so they should not produce significant heat.

I have very little experience with circuit design. I have found a number of flashing LED circuits on the internet but I don't know how to modify them to get the specific frequency range I require.

Any help in designing this project would be appreciated.