Picture too dark

Depends on the model. Have you checked the backlight, (LED in this set perhaps).

If the picture mode is set to Cinema or Custom, the screen could become dark. If the screen is still dark after the picture quality mode has been changed, change the setting Backlight, Picture, Brightness and adjust the brightness to your taste. ... Depending on such settings, the picture brightness level can be higher or lower

If Picture mode is set to Cinema or Custom, the screen may become dark. If the screen is still dark after the picture quality mode is changed, change the setting Backlight, Picture, Brightness and adjust the brightness to your taste. ... If Power Saving is set to Low or High, the screen becomes dark
https://www.sony-mea.com/en/electronics/support/articles/00024643

If your TV seems to be darker than you think it should be, it is possible that the problem is with the light sensor. The light sensor will automatically adjust the picture brightness based on the ambient light that is in the room, (i.e. if the room is bright the picture will also be bright, if it is dark the picture will also be dark).

To turn this feature off go to Settings > General Setup > Light Sensor.

This sounds like low screen voltage(A1)try adjusting the a1 voltage bottom control on flyback transformer if you have a voltmeter, voltage on crt base possible market screen or A1 shoud be beteen 350/500 volts when making adjustment remember to take into account current taken by meter If voaltage will not adjust flyback transformer will have to replaced

You don't say anything about the brand, but most have a menu or setup button on the remote (and TV) which give an on-screen display of functions available. You should see one for picture adjustments. Perhaps the projection bulb is getting old and dim. This is another possibility.

try adjusting the tint

try turning the light sensor off

*The brightness control setting determines how bright your picture will be. *The contrast control sets the gain of the video circuit. This determines the difference between dark and light scenes. Low contrast settings make the picture "hazy". High contrast settings make the picture more distinction between dark and light scenes. *The sharpness control determine the frequency response of the video circiut. High sharpness settings give better resolution but also shows more noise in your picture. Lower sharpness settings smoothe out the picture removing noise but also fine detail. It needs to be set for the best all around picture. *Picture Enhancement is pre-set adjustments which give you different picture qualities. You just select the one you like. Stargazer

hi solution #2 was correct. the adjustment knobs r on what's called the "flyback" i adjusted the bottom knob and the difference was from "night to day" !!!