Their critics say they are slow to warm up, the light flickers, and they are too big for some fittings.

BBC: The 60W bulb: A luminary love affair

Ironically, a red light also flickers when the markets hit a new high.

FORBES: New Highs Don't Lead to Selloffs

The light signal is consisted of a blinking pattern that flickers too fast for humans to see.

FORBES: Startup Targets Shoppers With LED-Based Indoor Navigation System