Check this out Developer brk3 has made a PRX plugin for controling the psps leds!
Hold L-Trigger + the Music Note button to turn off LED’s; press again to turn them back on. Copy LEDControl.prx to your SEPLUGINS directory and add the appropriate line to game.txt and/or vsh.txt — just like any other plugin. Enjoy!
--->> Download here
PSP Downloads | LED Control