Newer LCD monitors (and screens in some laptops) are being made with LED backlights in place of the previous fluorescent ones. These allow finer control of the light and so provide energy savings. The new Dell G-Series models are claimed to use half the power of their predecessors: 18W for the G2210 22-inch and 20W G2410 24-inch. One catch with this is that Dell is not offering smaller size LED models. The larger the screen the more power needed. So if you replace a 17 inch florescent back-light screen which uses 20 Watts (Dell E1709W) with a new LED 22 inch one which uses 18 Watts , you are only going to save 2 Watts (10% not the claimed 50%).
But there are some other power saving features of the monitors which may still make them worthwhile. They only use 0.15W in sleep mode, compared to 2 Watt for previous units. Also a sensor reduces the screen brightness automatically in dim rooms. The screen is also dimmed when displaying a mostly white image. Apart from saving energy, it can be painful for the eyes to be suddenly confronted with a very bright white screen.
The screens are also ENERGY STAR and EPEAT Gold compliant. A claim of being 28 percent lighter than comparable models seems a little odd, as LCD screens are not very heavy anyway. But perhaps this indicates less material is needed to make them, which is an environmental benefit.