[Tyr42]

Check out http://ledsmagazine.com/features/2/5/8 It says that:

The energy consumed by a 100-watt GLS incandescent bulb produces around 12% heat, 83% IR and only 5% visible light. In contrast, a typical LED might produce 15% visible light and 85% heat.

You can't always put a LED light in a enclosed fixture, as it might even overheat. It needs some air flow to cool it's heat sinks.

[abduhl]

The question is a matter of power then. A 100W bulb at 5% light is 5W of light (assuming power vs energy can be compared this way... I don't do electrical engineering) which would correspond to a 35W LED producing less than one half of the heat when you consider that snow piling up in front of a light and the light enclosure will convert the IR to heat.

[mkesper]

It can: http://en.wikipedia.org/wiki/Radiant_flux

Light measurement depends on the "use case":

Needed energy/power vs. How much "light" can be used by the human eye. Or, how good is the light suited for selecting pairs of (black?) socks: http://en.wikipedia.org/wiki/Color_rendering_index

That's why there are so many ways of measuring light: http://en.wikipedia.org/wiki/Light#Units_and_measures