Hi,

Use a power MOSFET with logic-level Gate Drive.
(You can drive it directly with the I/O of the microcontroller).

For my Stereo microscope ring light (warm white LED's) I use
IRLR/U2905 mosfets with I-Pak TO-251AA case. The microcontroller
and the LED's use the same power supply of 3.25V.
(20mA @ 3.25V for the used LED). The LED's are driven with PWM.

IRLR/U2905 datasheet:
http://www.irf.com/product-info/data...a/irlr2905.pdf

Best regards,

Luciano