Amstrad PPC 512/640 in Eternal Sunshine of the Spotless Mind (2004)
The PPC640 is used in the memory erasing process at Joel's apartment.
Suspending disbelief on the whole memory-erasing thing, this would still have been a 16-year-old machine in 2004.
The PPC640 doesn't have a backlit screen
PPC did not have a back-lit screen. At least not those I tested.
I would give it the credit that scientific equipment in realife is frequently interfaced with incredibly old computers. I use spectrometers controlled by computers that are 22 years old and can't be replaced as it uses a VESA local bus card and very specific software.
I would say that despite it's age of the time it's a groovy machine that does look quite scientific or military in it's look, so I can see why they chose it. I have one and can confirm the screen doesn't light up like that, so fair play they even modded it to look cooler than it is.