It's hardly a second order effect if you're talking about heating a space and the light is absorbed by the walls of that space.
replyIt's quite literally a second order effect. The first order effect is light generation, and a consequence of that effect is heat generation via light absorption.
replyDepends on where you want to draw the lines. Heating the room and emitting light could both be a second-order effect if you want to say that the first order is heating up the actual heater.
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