On Thursday, 30 May 2019 18:36:48 UTC+1, Jeff Liebermann wrote:

You're concerned about "heat" with measured in Joules where
1 joule = 1 watt/second
What I think you want is the final operating temperature of the device
to make sure that it doesn't melt plastic, degrade the LED's, destroy
electronic components, or set fire to the vicinity. The final
temperature has many parameters, most of which are NOT the same for
LED and CFL. For radiation loss, the surface area of a CFL lamp is
larger than the equivalent LED, and is therefore a more efficient heat
radiator. While the LED might waste fewer watts than the CFL light
heating up the room, the CFL will remove the heat from the lamp more
efficiently because it has a larger surface area. The LED compensates
for its smaller size by using aluminum heat sinks, while the CFL has a
larger thermal mass by using ceramics. Lots of other differences
making a general conclusion rather difficult.

What isn't obvious to me, having looked at the internals, is why the
orientation would have more than a trivial effect. That heat looks
pretty trapped no matter where the base faces.

Also maybe. The various lamps will move heat using conduction,
radiation, and convection. All three mechanisms are involved in
determining the final temperature of a lamp. In a light fixture, the
ability of move air through the fixture to remove the heat via
convective air currents is restricted. Without air flow the
temperature of the lamp will rise. If the air flow is uneven, there
will be hot spots on the lamp surface. Some lamps are more tolerant
to heating than others. My plastic case MR16 LED lamp was probably
the least tolerant. High temperature halogen incandescent lamps are
quite happy at much higher temperatures. LEDs lose half their light
output going from room temp (25C) to operating temperature (100C)
https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/heat.asp
which is why LED heat sinks are much better and larger than CFL which
can tolerate higher temperatures.


Heat radiation is not significant at LED operating temp. Ditto for most of a CFL, but the end filaments do run hot.

All heat produced by both does get dissipated, it can't be trapped else the thing would get endlessly hotter & self destruct.

Why does orientation matter? With a 20w CFL, the ballast silicon is vulnerable to high temps. Ballast down it gets cool air flowing slowly upward past it. Ballast up it gets hot air past it, reducing life expectancy. The tube OTOH doesn't care either way.


NT