Is light text on dark harder to read than the more common dark text on white? Or are there other factors?
First, just as an FYI, dark backgrounds are a problem specific to the old WCAG 2 math/method. And for that matter, evaluating predicted contrast using some other ratio maths. And let's not forget: maths like Weber and Michaelson are about threshold, but readability is far suprethreshold, so those methods are not particularly useful.
There isn't significant scientific consensus that goes much beyond user preference, and indeed some people (such as myself) much prefer reverse, light text on dark. The various dark mode extensions are quite popular for this. Also total screen luminance and the ambient lighting all are signficant here, and again one of the indicators of the importance of personalization.
Nevertheless, the old WCAG 2.x math badly mangles dark color pairs, in the randomized tests last year, dark color pair