The TARDIS hat was made as an accent piece to go with a TARDIS dress a friend was working on. It does everything a TARDIS hat should do -- it lights up and makes VWORP VWORP noises.
The frame is made from laser cut wood, using this pattern. Inside are six high power white LEDs attached to a central shaft. A double layer of frosted acrylic sheeting serves to diffuse the light.
Hidden in the dress is an electronics package and speaker. An Arduino and WaveShield provide the flashing light control and audio output. A remote switch allows it all to be triggered with a minimum of fuss.
Arduino source code is here.