Light-emitting diode (LED) based endoscopic illumination devices have been shown to have several benefits over arclamp
systems. LEDs are energy-efficient, small, durable, and inexpensive, however their use in endoscopy has been
limited by the difficulty in efficiently coupling enough light into the endoscopic light cable. We have demonstrated a
highly homogenised lightpipe LED light source that combines the light from four Luminus LEDs emitting in the red,
green, blue and violet using innovative dichroics that maximise light throughput. The light source spectrally combines
light from highly divergent incoherent sources that have a Lambertian intensity profile to provide illumination matched
to the acceptance numerical aperture of a liquid light guide or fibre bundle. The LED light source was coupled to a
standard laparoscope and performance parameters (power, luminance, colour temperature) compared to a xenon lamp.
Although the total illuminance from the endoscope was lower, adjustment of the LEDs' relative intensities enabled
contrast enhancement in biological tissue imaging. The LED light engine was also evaluated in a minimally invasive
surgery (MIS) box trainer and in vivo during a porcine MIS procedure where it was used to generate 'narrowband'
images. Future work using the violet LED could enable photodynamic diagnosis of bladder cancer.