Is HID really more efficient than LED? (I always ask this but I do it for testing purpose only)

The problem is is that the HID "equivalents" are too low. Really, a 50w HPS needs a 30-40 watt equivalent to be brighter. Instead they use something under 20 watts. I'm sure if you compare a 50w HPS lamp with a 50w LED, it would be brighter.

Whether anything is more efficient or better than anything else is always subjective. You can measure things scientifically, mathematically or however you like, but at the end of the day it comes down to two things. One, whether people like it or not, and two (and probably what most decisions are based on) - money. Most people want what's (apparently) cheaper.

Personally, Sammi and I prefer to pay more for a quality item that is going to last longer. We have a set of kitchen knives that probably cost getting on for £200 about 20 years ago. A friend who used to be a chef told us they were not what he would have used in a professional kitchen, but they were probably amongst the best domestic knives he had seen. Sammi bought those as I said around 20 years ago, so I don't know what they would cost at today's prices. But if she'd bought a cheap set for say £10, how often would they have needed to be replaced over a 20 year period..?

However, that's not how most people see things these days 

Sorry, probably not the best comparison with regard to lighting, but it was the first thing that sprang to mind (it's been a long day  )

Just to clarify how much the knife set cost, the cheapest one in the set was about £15.!! In today's money the whole set would cost about £270.

In terms of lumens per watt sadly no, you could have argued SOX, but when you factor in gear losses and lantern distribution as James has pointed out, the LPS lamp was still the best, but not as good as it looked on paper!
Where LED wins is in lower wattage lamps, something science and physics wouldn’t let happen in small HID lamps?
Although the only thing holding LED back in lamp form at the minute is handling the heat produced from the diodes, that’s why you can’t get ‘like for like’ wattages for HID yet, (for example, a 250 watt LED to replace a 250 watt HPS).

The other place where LED (and MH for that matter) fail is the white light. White light is simply not the best for road lighting; all the colours of the rainbow (literally) scatter like hell in rainy or misty/foggy conditions, making discerning contrast very difficult. The monochromatic light of LPS doesn't have that problem and is simply the best to drive under. When we encountered mile after mile of SOX on the motorway approaching London about 18 months ago, it was the best night drive I've had in years, I could actually SEE properly..! Any colour rendering you might need while driving is provided by your headlights.

Now maybe, just maybe, amber LED might approach that, but I've yet to see an example that comes anywhere near close. And yes, I'm biased and unashamedly so; I love and prefer SOX and always will 

There, that's me being honest 

Here’s a thought though?, an amber LED is just that!, amber!, I wonder if it’s even possible to make LED diodes behave exactly like a SOX?, or would it be ‘just’ a LED coloured amber?
I wonder if they can fine tune a diode to that specific 589nm region, otherwise they would be useless for a LPS stand in?
One for James me thinks? 

It is possible, but in these long wavelengths it would yield very low efficacy.
But the key point of using SOX was not much in being yellow, but in being monochromatic, so I would guess something in green region could do the job.
Definitely making it as a laser will make really monochromatic light (laser does not mean a focused beam, it may as well to be really diffused; the diffused laser would only exhibit a bit of interference moire).

I remember when we were kids, my friends family would always holiday in the Isle of Man, his mum always told me the street lighting there was green, which fascinated me!, I now guess she was referring to clear mercury lamps, but I wasn’t aware of them as a kid!