40 billion light bulbs can be recruited to deliver internet service through the power grid. They are already installed everywhere, even in planes. LED lights use little power. Visible light has 10,000 times more capacity than the radio spectrum. Security is simpler because it's easy to block light, hard to block a radio wave. The 1.4 million existing cell towers are expensive, limited in distribution and 95% of their power goes to make and take way heat.