The LEDs just fall backwards along their V-I curve and emit less light as the temperature increases. LEDs are constant current devices and are not (typically) driven in a way that allows them to compensate for this voltage drop by drawing more current. When heat is introduced, the electrons start at a higher energy level, and the voltage of the LED decreases. The forward voltage of the LED is indicative of the size of the energy gap an electron must achieve before it can be absorbed into the other side of the diode junction and emit light. LEDs emit light (and heat) based on the PN junction of the diode, which becomes less efficient as heat is introduced. When a filament bulb generates heat, that heat aids the efficiency of the bulb by lowering the electrical power required to heat the filament to the point of emitting light. That is an incredibly energy saving over the 10% efficient filament bulb, but still means that about 30% of the power consumed by the bulb gets emitted as heat rather than light. That “light energy” is what designers need to match with other sources to get an equivalent amount of light, which is why high-efficiency bulbs can call themselves equivalent to a 100W bulb while only actually consuming a fraction of that energy. While LEDs themselves can be extremely efficient, other components of the system like the driver or lens tend to reduce the efficiency of an LED light bulb to about 70%. A 100W tungsten filament bulb is about 10% efficient, meaning it only generates 10W of light energy for every 90W of heat energy.
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