The accepted optimal leaf surface temperature is somewhere around 78F-82F. Your room temp, and choice of lighting greatly effects the leaves temperature. I run LEDs, and aim for a room temp of 85 degrees fahrenheit.
You can use the gun on alot of things. Quick check of your lights temp, check on that wall socket with ten extension cords.
In my situation, you can see the difference between leaf temp and room temp when I aim the laser at the plants. Happy growing!