Where to place thermometer?

I have a very simple question guys:

I currently only have one digital thermometer and have been placing it on top of a pot facing upwards toward the light. What I did earlier is move the thermometer out of the light and the temp dropped 6 degrees!

Now, my 400w MH is about 13 inches from the tops and the plants feel cool...I am able to place my hands for over a minute and it doesn't heat up much. This is the best rule of thumb right?

But anyways back to the original question: Do I want to monitor my room temp by the temp directly under the light, or somewhere away from the light?

you want to measure canopy temp

I just did some searching and found out that its best to get a ambient temp than radiant temp. But of course its always best to do both. I need to shade the temp gauge from the direct light so that I won't get the radiant heat if I want to take the temp of the canopy.

put it at the top of your tallest plant for accuracy

I use my temp gauge's wire antenna and have it hanging at canopy level. That is the area of concern to make sure temp and humidity are optimal for growing.