People are comfortable with the familiar, uncomfortable with the unexpected. When a halogen or incandescent lamp is dimmed, less current passes through the lamp filament. The filament cools down, producing a warmer light with a greater proportion of radiation at the red end of the spectrum. As a result, we are conditioned to expect that dimming a lamp will produce a warm, relaxing ambience. LEDs produce light through a different physical mechanism — electroluminescence rather than incandescence. Here there is no significant color temperature shift when the current that passes through an LED die is reduced in order to lower its lumen output. You must design LEDs and solid-state lighting (SSL) systems to dim like halogen lamps.
Directional halogen lamps are popular in hospitality environments. But in these applications, the well-documented benefits of LED lighting over halogen lamps are desirable. In particular, LED light sources are far more efficient at converting electricity into light, so they save energy and run cooler. However, making an LED source dim with a similar color shift to a halogen source, maintaining color quality along the way, has presented significant technical challenges to designers of LED emitters and fixtures.
The aim has been to find an LED emitter that closely follows the idealized black-body curve as it dims. Better still would be one that follows the curve even more closely than halogen sources. To understand how this is achieved, it is important to consider the specific requirements for LED die, substrates, optics, and control electronics that make the halogen-style dimmable, directional LED fixture technically possible and commercially viable.