Feature comparison of three different light sources for fluorescence microscopy.

<p><b>A.</b> Brightness: optical power in an 8-nm wide wavelength band centered at 405 nm. Hg: mercury arc; Hal: halogen; LED: custom LED. <b>B.</b> Time course of photodiode current after switching illuminators on (upward triangles) and off (downward triangles): mechanical shutter and electronic LED circuit. Inset: detail of LED timing at shorter time scale. <b>C.</b> Noise spectra of light output as measured by a photodiode. Hg, Hal, LED as in (A).