Generally speaking, if you don't have a light-meter or a lux-meter to measure the light levels, and at the same time write them down, you're talking out of your sinus.
I have documented proof that new LED street-light systems are very typically brighter than the former HPS. Conversly, most parking or lot-lighting LEDs provide less lighting on the lots. In the near future, I'll be comparing the before lux levels to the burned-in levels to see how well the LED systems really perform.
Thermally activated degradation of phosphor converted white LEDs is a well known and documented problem, some large bulb manufactures like philips have even opted to dabble in remote phosphor lamps, but people don't understand how a yellow colored light is actually white when it turns on so now they hide the phosphor filters in an attempt to reduce this issue, but the main issue with street lighting is not the technology, because it's 100% doable, it's a lack of understanding the accounting department has of technology they know dollars not LED's, and they are the one's ultimately making the deal and the people who know the issues are the ones instructed to install them and they are all to often not given the opportunity to ask questions or make suggestions... So I would be willing to believe the cheapest fixture will be used and it will have a very short life time and it honestly costs more money upfront to build a high quality fixture that will out preform a tested technology like HID but the long term energy saving will pay off in the end, but don't try to talk to an accountant out of a short term realized gain on the books..
Just as a quick example you take a RAB fixture and an similar oversea's fixture, just look at the quality of the unit that will give you an idea of how long it will last,
One is machined aluminum and one is cast zinc,
One has nice optics, and full specs available, the other doesn't.
One can show the lumen decrease over time and they base lifespan on IES LM-80 results and TM-21 calculations, the other makes claims of 50,000 to 100,000 hours and that's it.
One is certified by other groups like International Dark Sky Association, COTS, ARRA and others, the other isn't.
One has a realistic warranty the other will dissolve the corporation at the first sign of trouble.
One also costs like 5 times more and, that is the one and only thing only thing an accountant see's $.