Well, when I used the IR light, I had to do different tactics then the instructions show. First off, like Caswell has said, it has to be done in a area that is "closed" such as indoors with windows and doors closed. Another thing is this, if the part is cold, like a 30 degree day, than it is going to take longer to heat up. Another consideration is the part size or density.
A large surface area and thin material will pull the heat away from the area being heated by the lamp. You will have to move the lamp closer then the recommended distances specify in the instructions.
A large, heavy casting will pull heat away from the area as well, but once the piece gets heated up it actually will melt the powder really well and be easier to control the temperature.
When I say placing the lamp closer to the workpiece I mean like having the light only 2" or so from the part, unlike the instructions say. The best thing to do is coat a junk piece, or even a few different junk pieces of varying material, like maybe a thin piece of sheetmetal and a heavy cast iron castin. This will be two different extremes and show you big heating requirement differences.
The IR lamps sold for hobby use may not be the easiest part to use, but it allows many people to do larger parts at a cheaper cost. It just takes more work to do it, you have to monitor the part closely compared to a large oven.
I suggest this, with the two metal examples I specified above, KEEP A LOGBOOK OF YOUR PROGRESS!!!! Try things the book does not say, what are ya gonna do
Hurt a junk part
? Who cares, you learn by screwing up stuff lol
In the logbook, write the type of piece you are coating, maybe even some sizes or weights, if you wish. Place the lamp next to the piece, record the distance of the lamp, check the temp in 5 mins, check again in 3 mins, if the temp is still rising, leave it there and check again every 3 mins. Once the temp stabilizes, either move the light closer or further away according to your desired temperature. Keep writing the temp every 3 mins, this way you know about when to expect the temp to be at a certain point at a certain distance. You have something to refer to for future pieces.
Again, as I said, you may have to move the lamp closer to the piece than the instructions tell you to do. So...if you do, record the distance as well.
Another thing, when taking the temp, what are you guys using? A IR temp gun
?? That would be the only thing I would use for this. Another thing, when you shoot the part with the gun, make sure you aren't getting a reflection of the light elements themselves for you reading, some colors such as black will give yo a false reading at times, depending on the angle you shoot the part.