On Mon, 12 Mar 2018 21:36:41 +0000, Harry Bloomfield wrote:

Scott explained :
Can I take it that where a lamp or shade states a maximum wattage, this
is for incandescent bulbs and any LED will be okay (on the basis that
LEDs use so much less power), or is the light intensity likely to be an
issue liable to cause fading?

An LED is very susceptible to damage from its own heat build up, much
less of an issue is likely heat damage to the shade it is in. If the
shade allows good airflow and cooling of the LED, likely it will not be
a problem.

That nicely sums up the issue. The incandescent lamp wattage rating for
any given lamp shade or luminaire is based on how much heat it can safely
handle. Incandescent lamps run at much higher temperatures than any LED
can survive (150 to 200 deg C ).

The problem with LEDs is that the LEDs themselves and any fancy
electronic ballasts have a maximum junction temperature rating of 125 deg
C meaning the whole lamp must be kept a good 30 to 50 deg cooler to
establish the required temperature gradient between ambient and the solid
state device junction temperatures within (LEDS and switching transistors
and diodes) to dissipate the heat generated by these devices.

The older, less efficient 81 LPW LED lamps were limited to the
equivalent American based 806 Lm 60W rating and even these only met their
claimed 25,000 hours life rating in open reasonably ventilated shades/
luminaires.

Now, it is possible to upgrade those 810 Lumens lamps with the 100W
1500Lm LED equivalent 12W 125 LPW lamps in those very same luminaires
because they produce slightly less *waste* heat than the earlier 810
Lumens 10W LED lamps did, meaning they will run just as cool, if not
slightly cooler, despite consuming an extra 2 watts for almost double the
light output.

The main benefit of yet higher efficiency LED lamps is not the power
savings they offer but the fact that they can be fitted into almost every
standard luminaire or lamp shade with almost no regard to the issue of
overheating that afflicted the early low efficiency LED lamps.

Most of the energy savings to be made with lighting were achieved with
the CFL generation of energy efficient lamps. Upgrading a houseful of CFLs
to today's modern 125LPW LED lamps will offer a vanishingly small
reduction in the overall domestic electricity bill.

--
Johnny B Good