My mom wants me to light a piece of artwork over her fireplace. I'm going to change out her existing Juno TC2 can trim from a 25W WH to a low voltage MR16. I don't know how bright I want this which got me thinking: if I put a 50watt MR16 and dim it, will that make it yellower than if I put in a 20watt MR16 without a dimmer. Something's telling me I'd be better off sizing the wattage without a dimmer rather than putting in the largest and just dimming it. Any other thoughts?

Yes, when you "dim" an incandescent lamp the filament temperature decreases which results in a warmer or redder illumination.

Generally, if you want accurate color rendition, you want to use a light source similar in temperature to daylight- about 5500k. Halogen (undimmed) is slightly warmer, around 3400k but better than regular incandescent. Metal halide comes close, so close that most motion picture sets are illuminated with them. Also very close are some flourescents. Check out the flourescent lamp product catalogs for those that have a color temperature of 5500k.

-Hal

Numbers aside, your eyes will not notice any difference in a dimmed 12 mr16 lamp. Use the higher wattage lamp dimmed down. This will give you the flexiblity of having the extra light if you need it and longer lamp life.

On the other side of the coin, if you dim the light considerably, you will find a substantial color change.

In addition, incandescent lamps get much less efficient when dimmed. A 50W lamp dimmed to produce the same light output as a 25W lamp will consume approximately 37W of power.

-Jon