LED fixtures are available in two formats. Dedicated LED fixtures that are built from the ground up with matched drivers, dimmers, etc., or retrofit LED bulbs that can replace Halogen bulbs in existing or new track fixtures. Dedicated fixtures are more expensive but usually of a higher quality than a system that uses retrofit bulb in old fixtures. There are also new fixtures specially designed to use LED retrofit bulbs with special vents to keep the LED cool, extending LED life and lessening color shifts.
There is lots of information out there on LED’s in Museums, especially on LinkedIn. Join the LinkedIn Museum and Art Gallery Lighting Group. There are several long discussions on LED lighting with lots of good advice and details. See “Can Museums Measure Up” initiated by Daniel Gelman from July of 2011. Even though the discussion is 2 years old and LED technology is advancing quickly, the advice on what to consider in choosing LED’s for exhibit galleries still holds.