It depends on the existing fixture. The voltage has to match, but there are options.

Some retrofit MR 16 led bulbs do not produce as much light, especially when compared to the higher wattage halogen MR16s.

Thanks Davidtay. What do you think about PAR20 LED instead? I was reading that the form factor of the MR16 makes them harder to cool. Do you think PAR20 bulbs would be more reliable?

Haven't tried them yet, but at least on paper these MR16s look terrific. 7 watts, 465 lumens, 95 CRI, 2700K or 3000K options, two beam spreads available, dimmable.

http://www.youtube.com/watch?v=DuxJ2HJf9-4

The heat performance characteristic of any LED lamp depends on a variety of factors such as-
1. the number and efficiency of LED emitters,
2. current drive
3. heat sinking used.

It wasn't too long ago that a certain brand of LED bulbs had an embedded cooling fan.

Some vendors may cut corners. The safest route is to stick to reputable LED vendors - e.g.: Cree, Philips, Sylvania

In the end, native LED fixtures may be a better alternative.

....except that Cree doesn't offer MR16s, and Sylvania and Philips don't have any with high CRI.

Is there any advantage using low-voltage 12 volt in LED applications? There could be with halogens, but it seems to me using 12-volt LEDs just adds expense without increase light quality or efficiency.

Yes, there isn't a Cree branded MR16 on the market yet. However, they do have a reference design that could match or exceed the performance of a 50W MR16.

Here is a link that might be useful: Cree MR16

Looks good, but I'm not ready to build my own light bulbs just yet. I'm surprised third party manufacturers would want to buy Cree components when they'll have to compete with Cree's own complete light bulbs. But I suppose small manufacturers don't have alot of choices if they want high-quality components..

I like their new LMH2 module with "sunset dimming" (I assume that means it gets warmer/orangeish when dimmed just like an incandescent); at full brightness it's 2700K, 92 CRI, 95 LPW, from 850 to 3000 (!) lumens. They're recommend for "high-end residential" use. Hope we don't have to wait long before these are incorporated into a complete lamp. Or can I just buy one of these and fabricate my own?

Time to launch another LED lighting venture via Kickstarter?

Cree does make a MR16 - it is called the 'LM16'. If I were looking at MR16s today, I would definitely consider them. If high color rendering were an issue, I would probably also look at the Soraa LEDs.

The 10w Philips MR16s have the built-in fans. Philips has been upgrading them over the past few years. When they first appeared at Home Depot, they were rated at 415 lumens, then 435 lumens, and currently 500 lumens. I have several of the 435s and a couple of the 500s. They replaced 50w halogens.

I just now noticed Cree sells MR16s - but only 83 CRI (and only 3000K) and isn't much of the point of using MR16s the high-quality light from those 12v halogens? The SORAA Vivid 2 and the Green Creative CRIsp are both 95 CRI as well as 95 R9 and high R13 as well, plus a choice of color temperatures, so on paper at least should give the vivid color renderering expected of MR16s.

I'm not up to date on the new terminology. About 20 years ago I installed some Halo track lights (110 volts). Yesterday, I went to my local lighting store, and they introduced me to some new track lights. Totally different geometry. They are low voltage with LED fixtures. They are available with douple-circuit tracks, i.e. each fixture can be set to use one or the other circuit so that they can be separately switched. They require two transformers, which would be switched at 110 volts, before the step-down I was surprised, however, at their cost (individual modules from $99 to $250). Any comments?

I'm not up to date on the new terminology. About 20 years ago I installed some Halo track lights (110 volts). Yesterday, I went to my local lighting store, and they introduced me to some new track lights. Totally different geometry. They are low voltage with LED fixtures. They are available with douple-circuit tracks, i.e. each fixture can be set to use one or the other circuit so that they can be separately switched. They require two transformers, which would be switched at 110 volts, before the step-down I was surprised, however, at their cost (individual modules from $99 to $250). Any comments?

I am getting ready to install two new track lighting runs, and am trying to get up to date on the most efficient setup, conscious of both cost and energy efficiency.

Any help for MTVhike and I?

I've done some more research and found that there are several companies which sell which I now know are called "monorail" lights. These included LBL, WAC, and Tech. As far as I can tell, they are not interchangeable, but each company has a wide selection. I would really like one which I can run horizontally between two beams, with rods hanging from the ceiling. Wiring from the ends would be a lot easier than from the ceiling.