What was meant by the charge: "the upsetting of the lamp"? In Justin Martyr's First Apology Chapter 26, we read:

And whether they perpetrate those fabulous and shameful deeds — the upsetting of the lamp, and promiscuous intercourse, and eating human flesh — we know not; but we do know that they are neither persecuted nor put to death by you, at least on account of their opinions.

The context is:

...the devils put forward certain men who said that they themselves were gods; and they were not only not persecuted by you, but even deemed worthy of honours.

But these three accusations seemed to have been laid against the Christians, charges which Justin supposed was rather invented by them that probably committed it themselves and then charged to the Christians: &quot;upsetting of the lamp, and promiscuous intercourse, and eating human flesh&quot;.
The &quot;promiscuous intercourse&quot; evidently referred to incestuous practices and &quot;eating human flesh&quot; to cannibalism which Eusebius confirms were charges laid against Christians,...

And some of our heathen servants also were seized, as the governor had commanded that all of us should be examined publicly. These, being ensnared by Satan, and fearing for themselves the tortures which they beheld the saints endure, and being also urged on by the soldiers, accused us falsely of Thyestean banquets and Œdipodean intercourse, and of deeds which are not only unlawful for us to speak of or to think, but which we cannot believe were ever done by men. Ecclesiastical History, V.1.14

Other non-Christian writers also refer to such accusations against the Christians that explains two of these charges in The First Apology , but I cannot find a meaningful explanation of what &quot;upsetting of the lamp&quot; means.
The phrase: “the upsetting of the lamp,” is a reference to the charge of incest, which is “facilitated by darkness.”

721 And anyone who makes use of them may in addition to [the guilt of] godless, impious, and intemperate intercourse, by chance be consorting with his own child or relative or brother. Some even prostitute their own children and wives, and others are admittedly mutilated for purposes of sodomy, and treat this as part of the mysteries of the mother of the gods—while beside each of those whom you think of as gods a serpent is depicted as a great symbol and mystery. You charge against us the actions that you commit openly and treat with honor, as if the divine light were overthrown and withdrawn—which of course does no harm to us, who refuse to do any of these things, but rather injures those who do them and then bring false witness [against us].

See footnote 721 here:

721 A reference to the charges of incest (facilitated by darkness) and cannibalism which other Apologists (Athenagoras, Tertullian, Minucius Felix) treat at length.