Late 2009 iMac Target Display Mode power consumption

I was just wondering if anyone has measure the amount of power an iMac (27" late 2009) consumes in target display mode. I have a desktop i7 Windows 7 PC hooked up to it through displayport to minidisplayport and it works great.. but I was a little worried that the i7 iMac would still sucking a lot of juice in the background. I'm assuming at idle most of the consumption is probably the screen anyway though.

It doesn't seem to ever enter a sleep state etc because I have logitech usb mouse connected to the iMac and its led remains lit, whereas in sleep it will turn off.

Any insight into this would be greatly appreciated.

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And I see I should have searched the forum more efficiently because I found someone asking the same question from december..

http://forums.macrumors.com/showthread.php?t=1504791

Looks like it might not be enough power for me to worry about.