LEDs for illumination do not use series resistors, they use switching regulators, which are about 85% efficient. The power is being dissipated in the LED, and you should expect about 3 to 5x less heat to be emitted for the same level of light compared to tungsten. Tungsten bulbs run at a couple thousand degrees though, so they have no trouble dissipating the heat. LEDs must stay under 100C or the doping in the silicon will migrate and it will cease to be an LED.
Thermal power flow behaves a lot like current flow: the thermal power flow (P) is proportional to the temp difference (dT) and inversely proportional to the thermal resistance (theta). P = dT / theta
dT(tungsten) = 3600 - 280 = 3320K
P(tungsten) = 150W
theta = 22 K/W
dT(LED) = 90 - 30 = 60K
P(LED) = 37.5
theta = 1.6 K/W
(A heatsink is a low-resistance thermal resistor. The larger surface area reduces the thermal resistance between the solid half and the air flowing past)
That tells you that for a 37W LED to maintain its junction temperature at 90C in a 30C room (typical design point), the junction-to-ambient thermal resistance must be no more than 1.6 kelvin/watt. That's a non-trivial heatsink.
The 150W tungsten bulb on the other hand will have a (designed) thermal resistance of 22 kelvin/watt so that it can reach the proper (3600K) temperature. The bulb size and thickness and gas mix are chosen in order to achieve that thermal resistance and therefore proper operating temperature.
For your purposes, the 150W vs 37W comparison is what matters, it means about 4x less heat and power consumption for the same light.
You can't use an LED on a dimmer unless it is specifically designed for that use and they will often not light at all (or just flicker very dimly) when switched by a solid state relay (triac), but they'll be completely fine with electromechanical relays. Yes, the problem is because they use a buck-mode switching regulator which has discontinuous input current, which means that if you run them from a triac, the triac switches off and you get no light.
If you buy LEDs, make sure they have high CRI (colour quality) and a colour temp of either 5400K (daylight) or 3600K (tungsten orange). Do not buy anything with a 6000K or higher colour-temp; it will look disgustingly blue. If you print colour, the CRI of your light sources should be greater than 90 or you will have serious problems.
Last edited by polyglot; 01-19-2013 at 11:47 PM. Click to view previous post history.