This relatively simple circuit uses a 6-V DC supply with a PWM current-source configuration to provide efficient, adjustable dimming of a white LED over a wide range, needed to accommodate the unique lighting needs of an optical microscope over its magnification range from 40× to 1000×. by James Campbell
When the built-in incandescent light source of my venerable Olympus microscope failed after many years of use, I decided to design a reliable modern replacement. A 1-W white LED (SEOUL X42182, 350 mA max, Vf = 3.25 V) was the obvious choice to provide high brightness and full-spectrum light without the heat of incandescent or xenon arc lamps. The microscope lamp brightness needs to be adjustable, however, to accommodate the different objective lenses, which offer magnifications from 40× to 1000×.
Current Source For LED Microscope Illuminator Provides Full-Spectrum Light – [Link]