Being an older monitor, I was wondering how bright it was supposed to get, 300cd/m^2 apparently, which ain't all that bright by modern standards. Also I notice it has an illumination sensor to modulate brightness, which if using in dim lighting might not get you full brightness. See if you can see a sensor anywhere, if it's in a stupid place like on top, maybe having it back in a hutch shaded it or something. Try shining a flashlight straight in it to see if the screen brightens, also check it for dust/debris.
edit: you might wanna check out the settings, if it's in full eco mode or something then full bright might not be achievable, my Toshiba TV is very dim in power saving mode.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.