is set at a fixed distance of 5 cm from the end of a shoe in which shoe tree 200 is installed the reason for such bulb placement is that the intensity and therefore the effectiveness of uv energy as a sterilizing agent decreases with distance away from the light source spring carrier 328 which is formed of two matable u shaped rails 344 contains and secures in its interior an end 346 of coil spring 322 spring carrier 328 is fixed by a pin 350 to clevis 326 of spread plate 320 fig5 shows coil spring 322 passing through a tubular housing portion 352 in the forward end of heel section 208 and an end 354 of coil spring 322 resting against a stop 356 in the rear end of heel section 208 coil spring 322 is held in a nominal partly compressed state in spine 206 a strain relief clamp 358 holds cable 288 in position on housing portion 352 of heel section 208 as spine 206 undergoes changes in length an articulated rubber sleeve 360 positioned between forepart 204 and heel section 208 fits over spring carrier 328 and conceals it from view fig5 and 6 show a photo interrupter 370 which includes a spaced apart infrared ir transmitter detector pair a fin 372 attached to the back end of u shaped rail 344 obstructs ir light emitted by the transmitter from reaching the receiver when coil spring 322 is in its nominal partly compressed state compression of spring 322 as shoe tree 200 is placed in a shoe causes fin 372 to move rearward thereby allowing ir light to reach the.