Using a temp gun

[Hugsplox]

The temp guns measure whatever that laser beam hits first. So, if you're trying to go through a screen top that has extremely small holes, chances are you're going to hit the screen, which in turn will give you the temperature of the screen. If the screen holes are large enough, and you can pass through without hitting the screen, then it'd measure the surface, or wherever you're trying to aim at.

To add to what Charles said, your temp gun should have come with a little booklet that will tell you what the effective distance of it is as well so you can make sure you're getting the most accurate readout. I'm sure you're well within the distance but some of the less expensive temp guns you have to have it within 6-12 inches of what you're measuring or it won't be as accurate.