There is a whole range of newly emerging techniques that have traditionally employed laser light to illuminate a sample, but are now turning to LEDs.
Until recently, spinning disc confocal microscopy systems featured laser illumination due to light loss through the system.
In neuroscience, there is a long-standing desire to selectively target one cell type for investigation without affecting other cells in the sample.
LEDs are not just used for illuminating a sample in time-lapse microscopy. They are also used in most focus drift correction systems (from manufacturers such as Leica, Nikon and Zeiss), which are feedback devices used to maintain focus.