Fig. 2.

Optical power output and spectral stability. The battery-powered device achieves excellent optical power stability at any given operating current but (as expected for an LED device), exhibits spectral shifts to increased l at higher current (and power). (a) Measured LED output power (after fiber) is stable up to a driving current of 8A. (b) Total optical power output increases with driving current as expected, but with diminishing returns at higher current. (c,d) Spectral data showing LED peak emission wavelength at different operating current after a 1-hour continuous operation (c).