Solar Powered LED Streetlights

Every night, there are millions of streetlights burning electricity to keep the urban jungles and roads safe.  The technology for streetlamps hasn't changed much, when it gets dark they light up high intensity light bulbs that burn quite a bit of energy. 

Why aren't all streetlights off-grid?  Why don't they have solar panels on top, and LED's for lighting?  Why It just makes sense, right?  Well apparently Lighting Science Group is making a go at it with their PROLIFIC Series Roadway LED streetlights.  The best part is that their 100-2att, 5000k Roadways are at least 50 percent more efficient that HID's.