Not a stupid question at all! I burned my first plant not thinking it through. I agree with Scotty ^, if you're going to have one, then dangle it at the height of your plant tops, under the light. That means as the plant grows, you're raising the thermometer, too.
In my tent, there's a 20 degree difference between the tops and the bottom, especially well into flowering when the bushiness blocks light to the lower third. That's under a 400W HPS.
The most important temp is the one by the tops so that they don't burn.