LED can do what streetlights do , but not at the same cost. LED produce light, the same light as anything else. Light is generally measured in lumens. 60Watt incandescent bulb produces 750 lumen. The LED in something like a power light on your monitor would require about 25 to produce 1 lumen, so 750x25 = 18,750 LED to produce the light of a single 60 watt light. That is the lowest end of LED lighting though and Cree has the new series that output 1000 lumen . The power cost is about 10 watts. The modules sell for around $75 each with heatsink and lens. To mount that in a street light enclosure and provide the necessary power supply you are at about $225 not including install cost. Estimate install at $200 max and for about $425 you can equip streetlights with LED.
So why not re-do all the lights ? Cost. A replacement bulb for a street light is $6.
I support CREE though because they are a major USA employer and my state benefits a lot from them since they are headquartered here.
They do offer a ready made streetlight
http://www.betaled.com/us-en/LEDProducts/LEDStreetLight.aspx
One other thing LED can do that current street lights cannot is DIM. LED can go from 0 to full bright and anywhere in between in seconds. Sodium based lights cannot.