Here's a video showing a OVX getting LEDized with a corncob lamps. I'm surprised that for a freeway application they bothered to retrofit with a corncob instead of changing the luminaire. 

Note the rare mirror finish lamp originally in it. 

Judging by the brand of corn cob used, I’m sure the improved OVX probably produces half the output of the original lamp, especially at that height. I think a new LED luminarie would have been more appropriate to be honest.