It's funny, because I've used a lot of ghost lights to just create that ambient light so my renders look bright enough on Android. But they're really buggy and obsolete at this point, and they seem to bump up the render times by like an hour. I said 'fuck it' and deleted all the ghost lights and all of the sudden the ceiling lights in the environment showed their actual luminosity, which looked like stepping into the light when you die. Those lights didn't even appear to be on because the presence of ghost lights makes that light invisible in the viewport. Once I dialed it back, I had the same effect and I cut an hour off my render time. So far I've learned how much ghost lights hurt more than they help with Daz. Anyhow, now I'm trying out your suggestion. I'll send another when I get it right.
yeah, the material lights always had problems, but daz really broke them for good in 4.16 or 4.18 version or around that time. and the problems get MUCH worse if you have any transparencies in the scene which give just unpredictable behaviour which can't be fixed. like if you had decals with transparency, like a wound projected on the skin, the transparency just flat out stopped being transparent and you got the square edges of the wound opacity map 100% visible regadless of opacity slider. but when you switch material lights off, boom, transparency works again.
also any lights with render-emitter set to 'off' will be visible behind any transparent materials, but I don't think that's just with material lights.
for a while I tried to work around it all, but in the end I just removed all material lights and replaced them with spherical spotlights or rectangle ones, depending on case. like for light shining in from windows I have a window-size rectangle spotlight right in front of the glass (inside the room), where as before I used to have a similar square plane with material emission turned on in the surface tab. and like you said, the spotlights are even much faster to render now so it's another reason to avoid material lights.
I still have SOME material lights left, but only where they're not supposed to illuminate other surfaces, ie. they're set so dim that they look glowing but it's not enough to light up anything that's not super close.
another thing I've noticed is that dark/night renders are now SUPER fast with spotlights, where as material lights make all low-light scenes take forever.
(I should probably mention I have a 3090rtx, so on a non-rtx gpu what's fast or slow might work differently.)
oh, if you have problems with some individual surface looking blindingly bright, the hacky workarounds I've used are 1) changing the diffuse color of the surface to darker (which can make colors dirtier so has limited use), and 2) adding some translucency to the surface even if it's not IRL supposed to have subsurface scattering, but a little translucency seems to have a tendency of 'sucking in' some of the excess light. you just have to be careful it doesn't begin to look waxy, so also of limited use. often the most 'natural darkening' is acieved by adding a little bit of both.
also make sure your specular, dual lobe specular, glossy layered weight, top coat weight etc are low or zero if you're having brightness problems. I don't think these are modelled correctly on any shaders I've seen and sometimes they just clearly work wrong and your surface is blinding bright no matter what you do.
also check that the shader is set to specular/glossy and not metallic, as often you can't disable brightness from metallic shaders even if you turn everything to zero. they're simply not meant to work without specularity, so if surface is blindingly bright it can't be turned off.
these hacks also become useful as often making skin look right requires LOT of light (precisely because subsurface scattering sucks more light), which makes all other surfaces blindingly bright. if the skin gets too little light, it usually looks lifeless and sick. this is yet another error in how daz treats lights which we just have to live with.