HDMI/USB Powered Lighting
HDMI sinks must not consume more than 50mA of current, and HDMI sources must provide up to 55mA with a current limit of no more than 500mA. So no, you can't really power anything directly from HDMI sources. But you can use the 5V power output as a logic signal to control LEDs that are powered from an external power supply. But many HDMI sources just keep the 5V on all the time, so most likely this is of no use.