An A320 pilot comments that CRT readability is decreased during bright ambient light conditions. The air carrier maintenance did not replace the unreadable CRT.

Narrative

Captain CRT written up in cruise for being too dim. By the time I flew a few specific heading in the pattern (downwind and base leg); I could not see a thing on the PFD. I considered just giving the aircraft to the first officer to have him finish the leg; but I knew as I made a turn the CRT would be shaded just enough so I could see it. Conditions were clear; so the flying part was as easy as the Cessna days; but if a TCAS event or wind shear event were to happen I wouldn't have been able to make out the warnings let alone seeing flight director or FMAs. Neither of the irregular conditions were likely; so I flew looking outside with First Officer's PFD and standby instruments as a crosscheck. During cruise I sent maintenance control a note to tell them the lower ECAM screen looked good -- I would have hoped they would swap it in LAS. I got no response from maintenance control. After landing I debriefed contract maintenance -- he assured me he was 'all knowing' and he would fix it. I went back and checked; no swap. They gave it the standard 'cleaned screen operations checks normal.' I don't know the outbound Captain or his motivation for flying the plane without a fix. I did not get a chance to brief him on the problem; my only guess is he is one of the folks who just puts up with the problem as 'a bus thing.' Lately I have not checked up on maintenance because it is the same old story -- if time or parts are short; cleaned screens operations normal is ok. If I stand there and discuss with the mechanic the merit of his eyeball in the dark or even under an overcast versus ours in the bright direct sunshine; some will fix it. If not -- I will refuse it every time the dimness is a factor.Callback conversation with reporter revealed the following information: The reporter's aircraft have CRT screens in the flight station. They are initially de-tuned prior to installation for longevity; but over time become dimmer as the CRT ages. His air carrier's maintenance addresses pilot's CRT write-ups by cleaning the screen; cleaning the ambient light sensor; checking the brightness knob's function; and finally turning the screen off and then on. If it performs in any ambient condition it is considered functional regardless of the apparent lack of readability in bright ambient conditions.