Temperature Measurements - where to take them?

Is it best to measure temperature at the soil, or at the top of the plant?

The top of the plant is closest to the lights so its hottest, but its several degrees cooler at the soil level. So when all the guides say its best to keep temperature within a certain range, is that talking about at the soil level, or top of the plants? Or midlevel? Or....?

Thanks

I personaly lay a thermometer flat inbetween my pots and have another on the wall a few feet away and another down on the floor.... I like to keep my perimeters temp under heavy watch....

i was always told that you want to take the temp reading at canopy level, as this is where you really want to know where the temps are at.. and like you said, it tends to be the hottest spot in the tent, so if it's ok there, it will be ok everywhere..
plus, it's where the plants live at, so it's the most important area..

both if possible. 78F is optimal.

although my outdoor soil temp is usually around 100F