Integrated Vs. Discrete Graphics
As already mentioned, virtually all graphics cards are power hogs. The difference between integrated graphics and even a low-end graphics card is so significant that it exceeds the difference between an average processor and a very-efficient model. Or in other words, the power savings in idle mode by running an efficient processor are completely negated as you plug in a discrete graphics card!
Let's look at the chart above as an example. ECS's G33T-M2 MicroATX motherboard required 53-W idle power in our last Intel MicroATX motherboard roundup with a Pentium Dual Core E2160 processor, which is basically a Core 2 Duo with only 1 MB L2 cache. However, utilizing a GeForce 8600 GTS graphics card would increase the idle power requirement by 31 W to 84 W. A GeForce 8800 GTS, which has more shaders and higher clock speeds, even raises the power requirement to 122 W, which resembles a doubling of the initial power draw. And that's not all: As you switch to 3D mode to play a game, the power requirement will further increase by another 60 W, as you can see in the following chart.
Single Graphics Cards
These are the power requirement measurements we took from various graphics cards for our 2007 VGA Charts. While we don't really have a problem with maximum power requirements of up to 200 W for Radeon HD 2900XT and GeForce 8800 Ultra cards (you want fast and beautiful graphics), we can only shake our heads looking at the idle power requirement numbers. We measured these under Windows when the graphics cards weren't actually displaying anything except drawing the Windows desktop. A GeForce 7300 GT or ATI's Radeon X1300 will start at approximately 20 W idle power, which still is quite a bit, and mainstream graphics cards typically require 30-40 W idle power. Knowing this, using a discrete graphics card does not make for a power-efficient computer, because 20-90 W idle power is as much as an entire PC with integrated graphics requires.
I don't mind the graphics card requiring 150 W if I'm in the middle of a 3D game or a demanding 3D application. But idle power requirements of a powerful 3D graphics card exceeding the power draw of an entire office system for a business PC is totally unacceptable.