Is it safe to put a 120W equivalent LED bulb in a 100W max fixture?
Yes, that is fine
&quot;like&quot; /&quot;equivalent&quot;, etc. are based on light output.
Limitations on fixtures is based on heat output.
Some power (Watts) becomes light, the rest becomes heat. LEDs are more efficient and produce more light, and therfore less heat, than incandescent bulbs. Fixtures are rated on worst case scenarios. But a 15 W LED bulb can only put out 15 W heat. No problem.
It may be that fixture power rating is based on efficiency and expected heat output of standard incandescent bulbs, rather than total power output. But that would make very little difference. A quick search finds incandescent efficiency in the range, at best, of 5% to 10%. If a 100W incandescent bulb is 10% efficient (very optimistic) then 90% of the power - 90W - is lost as heat. If the 15W LED produced entirely heat and no light at all (which wouldn't be too useful), it would only produce 15W of heat. No contest.
All that being said, there can be heat issues with LED lighting. Generally this is with new fixtures designed specifically for LEDs, not putting LEDs into standard Edison base fixtures. In fact, some high-power fixtures include fans to dissipate the excess heat. This is because (a) an LED can be extremely compact as there is no functional need for a large &quot;globe&quot; around a filament (when there is a &quot;filament&quot; in an LED bulb, that's just for show) and (b) the driver circuitry between the incoming AC power and the actual LEDs produces heat. This is also the reason why some LED bulbs will specify &quot;don't use upside down&quot; - heat rises and if the heat is all generated at the bottom of the bulb and you install it upside down so that the bottom (as designed) is at the top, heat may not dissipate properly.