LED lighting

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I think that's probably a good summary - only a proper examination of the subject will confirm it.

On that basis: lumens output per electrical watt input provides a measure of the efficiency* of a lamp, but I think lux is probably a better measure of its usefulness.

* The sources seem to prefer the term "efficacy", but I don't understand the distinction.
Mikes link above said:
As a frame of reference, a standard 120V/60W light bulb is rated at 850 lm, and the equivalent 230V/60W light bulb is rated at 700 lm.
Why would the voltage make a difference when the wattage is the same?
Why would the voltage make a difference when the wattage is the same?
Presumably lower voltage bulbs are more efficient at producing visible light. I don't know why but as they will have thicker filaments I'd guess that may have some effect on the function.

Pretty early in this thread I was bemoaning the non-uniform output of LED lamps compared with the GLS I wanted to replace. Unless it's a single-lamp fitting, the light distribution can be largely compensated by using a fitting which angles the lamps in complementary directions, but of course I'm too tight to consider entire new light fittings.

(BTW: I regularly pass a lighting showroom with all manner of weird modern lighting I wouldn't give house room nor have the space for, because of the artistic opportunities offered by distributing individual LED chips over a surface rather than as a replaceable module, but new regulations for repairability are going to shake all that up!)

The irony is that I have a couple of reflector bulbs where I want directed light with little overspill, one has failed, and now incandescent spots (or any other incandescent lamp) is unobtanium off the shelf. I bought a pair of cheap R50 SES form-factor LED lamps to plug the gap, but although they fit the fitting these do not perform the desired function of providing directed light.

In fact, I didn't even used to have standard R50s in those fittings, my preference was the narrower beam version with the bevelled edge, so the 180º spread of these LEDs is a bit of a shock.

af123 was extolling the virtue of reflector LEDs:
I've just replaced four halogen R63 spots in my kitchen with these and they're superb. Can't tell the difference at all apart from a brief delay in turning off once the switch is thrown.

...but that website no longer seems to be working. Any ideas?
That site lists six R50 options, three of which are 110º+ and three 36º beam angle. Interesting.

(The site itself is slow and unresponsive on my bandwidth!)
@BH My bandwidth is good but I had similar issues and blamed my VPN. At least it gave you some food for thought.