I got samsung notebook SENS Q210, when i unplug the power adaptor the screen light will become very dark so what is the brightness setup on screen solutions?

The screen may become dark if Picture mode is set to Cinema or Custom. If the screen continues to remain dark after changing the picture quality mode, go to the Backlight, Picture, Brightness menu and adjust the brightness to your liking. When Power Saving is fixed to Low or High, the screen becomes dark. Some TVs have a Light Sensor so the picture will just become brighter or darker depending on the lighting in the room.
You can also try programming from a different source, like a DVD player or VCR to check whether the problem is caused by the device that sends the signal to the TV.

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

Any sound? Does the HDD led blink during start-up? Can you hook it up to a external display? If so, what is on the screen?

Press Ctrl , Alt & Up arrow key together...

Check the power saving options.

It will because when you unplug the Power cable, it will automatically switch battery mode. When in battery mode it also activates a kind of Power saving mode by default. Thats why it seems dark. Now if still want to brightness then remove adjust the brightness level while the laptop is on Battery Mode but i must tell you, your battery backup won't last too long.

I spoke to Garmin Support about this issue. There are 2 settings for contrast on the nuvi 1300. You need to set the contrast while it is plugged into the vehicle, and also while it is unplugged from the vehicle. The reason for the 2 settings is to save the charge of the battery while it is not plugged into the vehicle or power source.

check inverter board.

look at the screen held in a bright light at an angle do you see the desktop dimly .
if not try the function monitor key,
connect an ext monitor to verify the video card is working ,fn monitor .
if you see the desktop dimly then the inverter may be out or the lamps.

If the LCD screen is too bright or too dark, adjust the LCD Brightness setting in the Setup Menu. If you are shooting photos outdoors in bright light, move the joystick to the icon showing the sun over shaowed area to turn on Outdoor mode and make the LCD screen easier to see in bright light.