DJDarren, 
Granted these monitors are from different manufacturers, but the Philips really shouldn’t be 1/3 the brightness of the Dell.
Using my light meter in an unscientific way suggests that the Dell is 360lux. The same point on the Philips is 115lux.
Is the Philips just shitty, or is there something I’m missing? I’ve got BetterDisplay installed, but that can’t make it any brighter.