GU5.3 LED retrofit recommendations please

I'm looking at replacing the 12V 50W halogen lights in the kitchen and bathroom with LED. I expect many of you have done similar. I'd be interested in recommendations, particularly concerning:
1. Compatibility with existing halgen power units. Each halogen unit has its own "transformer". Philips seem to claim above average compatibility.
2. Brightness. Can any LED match a 50W halogen?
3. Angle of beam. I expect the halogens are very wide.
4. Colour Temperature. Both kitchen and bathroom are very white (white celings, off-white walls). Does this imply a cold white / high K temp is most suitable ?
5. Price: There and many very cheap units on eBay, etc. I'd rather pay a bit more and be happy, but if you can recommend a good, cheap source, then great. Philips seem more expensive than most.
I did think of buying a few different units to try.
Thanks in advance. Fred
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They usually won't draw enough power to keep an electronic tranformer on. Yours are likely to be 20W-60W units - there aren't any 20W retrofit LED MR16's because there's no way that form factor can dissipate 20W and remain below max LED junction temperature.
I would replace with GU10 fittings (mains), dispose of the transformers, and use GU10 LED retrofits, of which there is a much wider variety available. Choose fittings which hold the lamp at the front face and have a floating lampholder if you can - this enables you to fit larger (higher power) GU10 LEDs, which are longer than conventional GU10 halogens.
If you really want to keep the MR16 fittings, you will probably have to run at least 4 of them from a 20W transformer, or replace the transformers with ones for 12V LEDs (which is a waste of money). You might be able to find just the GU10 fly leads, and use those instead of the GU5.3 fly leads in the original fittings.

For a 12V 50W halogen: Centre beam - yes, but total light output, no. For a 240V 50W halogen (which is much less efficient): pretty close.

Halogens have more spill outside the main beam. This is often regarded as a bad thing, but when you use downlighters for general lighting, you are rather dependant on that spill to provide the general lighting (which is why downlighters are a bad choice for general lighting). When you switch to LED, you may not have anywhere near enough spill, depending on the lamps used.

Personal choice. Your 12V halogens will have been about 2800K, or 2700K if they were long life. If the rooms are brightly lit, you can generally go for a slightly higher colour temperature. Anything over 3500K will probably look silly in a room lit at evenings/nights, and doesn't work for food preparation in kitchens where you need a significant proportion of red light to assess quality of raw meat.
--
Andrew Gabriel
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You will remove the losses of a transformer by going to mains GU10s as well.
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LEDHut or Lightrabbit. 5 year guarantee and not a failure yet (nor on any of the Aldidl ones). Otoh, the cheapy Chinese ebay ones and aliexpress have all failed on me.
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Thanks for all your replies.
As I understand it, the recommended GU10 LED is:
1. Mechanically identical to the GU5.3 halogen, so drops straight into lampholder.
2. Has a different connector and flylead. I see these on eBay very cheap.
3. Operates from 240VAC, ie no external switching supply needed
4. Points about: a. colour temp. b. beam angle. c. reliability of different sources. all noted.
Digressing back to the GU5.3. I have in my career designed switch mode power supplies, and I always tried to make them work down to zero current load. I have noted zero output from some GU5.3 supplies without load.
Thank you.
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But LEDs don't run directly from the mains, so it would depend on the design of the LED electronics versus the 'transformer'. And my gut feeling is a well designed 12v SMPS might well be more efficient than something you can cram in the base of a bulb.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sun, 30 Nov 2014 13:56:14 +0000 (GMT), "Dave Plowman (News)"

I see both arguments. GU5.3 and GU10 both have switching supply in the base. So with GU5.3, that's 2 series switching supplies (transformers). Fred
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Andrew Gabriel wrote: trim

That answered a lot of questions for me.
Bill
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