"Supertropes I Hate" is a special Supermonth series dedicated to tropes in Superman storytelling that I just can't stand. If I never saw this trope used again, it'd be too soon.
We all know that Superman, in the modern age, derives his powers from Earth's yellow sun. His body is a living solar battery, absorbing sunlight both to provide some measure of sustenance and to power his amazing abilities. In point of fact, his body naturally absorbs sunlight, regardless of the color, it just happens that yellow sunlight supercharges him.
He stores this yellow sun energy, so if he happens to be away from a light source for an extended period of time, it'll take a little while before his powers fade entirely. When the sun was snuffed out in "Final Night," Superman still had his powers for several days, maybe even weeks, afterward. How long he's able to maintain a charge naturally depends on how much energy he's expending.
Under a red sun, like the one Krypton orbited, Superman's body absorbs much less energy. As with any time that he is not exposed to yellow sunlight, the charge will eventually wear off, depending on how he uses his powers.
This is how Superman's powers have been defined in the modern age, and it's a fantastically logical (inasmuch as that word can be applied to comics) way for his body to work. Contrast this with the Silver Age, where there was some sort of magical on/off switch for his abilities, corresponding to the yellow and red suns. Shining red sunlight at Superman would make him instantaneously human; there was no stored charge, no battery effect. Superman lacked capacitance.
Despite the fact that Superman's physiology in this regard has been fairly well-defined, some writers still treat red sunlight as an off switch to Superman's abilities. They would have you believe that Superman can be totally undone by a heat lamp.
The worst part of this trope is how easy it is to explain away. All of Superman's powers use energy from his internal solar batteries, including invulnerability. A red sun lamp won't sap Superman's strength, but a super-intense burst of red sun energy will require the (passive) use of his invulnerability, which does sap his energy, provided he isn't being continuously charged by yellow sun exposure. The red sun generator just has to be powerful enough to make him burn through his energy stores by using his invulnerability.Or, you know, sap his powers some other way; the red sun lamps just ensure that he won't be recharging what he uses.
Superman's powers aren't that difficult to understand, and it bugs me when people make basic mistakes like this one. One line of dialogue, one difference in the art, could clear up this trope each time it pops up. Instead, we have situations where villains think you can drain a fully-charged battery by giving it a tiny charge. It's inconsistent, it doesn't make sense, and it needs to go away.