Temperature Readings: PE2 vs Herpstat Probe

Having just set up the new enclosure, I will run it for a week or so to ensure that everything is working properly before picking up our new dragon.

I have an Exo-Terra 150W Daylight Basking Spot in an Exo-Terra Light Dome mounted over log which angles upward to a ledge, with the bulb being 8-9" above the lamp at its closest (the ET site notes the bulb should reach 109 @ 8"). I have the lamp controlled by a Herpstat 4 with the lamp set to Heat (Dimming) and basking assist enabled. I have the temp set to 104 and the probe consistently reads 104.

I also picked up a Pro Exotics 2 temp gun, but when I measure the temp directly beside the Herpstat probe, it reads anywhere from 109 - 115.6 measured from about 4". I have never used a temp gun before and the instructions with the PE2 don't offer anything regarding calibration.

If it was only a degree or so difference, I wouldn't be concerned and given that I keep getting different readings for the same spot with the PE2, I am inclined to rely on the Herpstat probe.

Anyone have experience using these two pieces of equipment, who might be able to offer some insights?

Had to look the gun up. http://www.ultimaterc.com/reviews/pro-exotics-temp-gun-pe1-pe2/
Specs


The Habistat probe will be accurate , you can improve the accuracy of the readings from the PE-2 but you need to know :
1) the exact material in the basking spot (so you can get the correct emissivity for that surface and material, this will make a noticeable difference.
2) get the measuring technique right , be careful of specular errors.

Refer to these for more information :
refer to information : viewtopic.php?f=34&t=239064&p=1833542#p1833542
and this explain more : viewtopic.php?f=34&t=241233

It is possible to compensate for emissivity errors but the calculations involved will be beyond most reptile keepers who don't have the necessary physics or engineering education , the existing IR gun is likely 20 to 30 degrees Celsius out when reading the surface temperature the "NON STANDARD SURFACE (which has a emissivity significantly different to the standard e (gun) = 0.95 found with cheap IR guns who have no emissivity adjustment).




The brief explanation is as follows : the Stefan-Boltzmann Law gives the radiated infrared energy emitted by a target surface and shows this is exponentially related to the absolute temperature of that surface.
The equation is E_b = εσT^4 where ε is the surface emissivity and the true surface temperature is calculated using this equation

Thanks, appreciate the info. I will try adjusting the emissivity level, guessing at the type of wood (hard and dense - likely some type of ash) and give it another go, making sure I measure correctly.

Cheers, James.