Voltage. If you live in or near a major city, your voltage swing can be 10% . This is the maximum most utilities allow. This means your voltage could swing from 125 volts to about 112 volts. If you use incandescant lighting, this means a 10% drop in output from 125v to 112v. This drop in light output will translate into a drop in emitted IR as well.
Try a different type of light, like a halogen. They aren't as susceptible to voltage swings for emitted IR (if you've ever noticed how hot they get) as well as cycling at 60 Hz.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.