[tscs37]

It appears to be brighter because LED parts occupy a different spectrum. Sodium lamps only light up in a very narrow orange spectrum of light (you can't even tell colors under sodium lights). This spectrum is great under photopic vision (ie Daytime Vision) but terrible under nighttime vision. (~0.8 relative brightness vs ~0.1 brightness)

LED lights used for street illumination use a part of the spectrum that is much more visible during both day and night vision.

There is of course also a tradeoff because making a lamp more visible and thus allow safer driving, it will disrupt the circadian rhythm much greater.

It is certainly possible that the illumination is exactly the same but the wavelength of light outputted is different and you're much more sensitive to it.