Bright neon green light lights up horizon.Heading East on I-70 towards Portales, NM, in pitch darkness, no oncoming traffic or any other vehicles on the road but our own 2 vehicles. Suddenly, a bright neon green light that lit up the horizon appeared directly ahead of us off in the distance. The light appeared neon green for about 5-7 seconds then turned into a bright white for about 3 seconds before completely diminishing.