you will have to use an IR thermometer

if you don't have one.. you should get one… they are 10 bucks or less at most discount type places.

http://www.banggood.com/Wholesale-Mini-Pen-Type-LCD-Non-Contact-IR-Infrared-Thermometer-Gauge-Meter-50-To-220-p-65333.html?currency=USD&utm_source=google&utm_medium=shopping&utm_content=miko_ruby&utm_campaign=Electronic-xie-us&gclid=CIr0oYbwtroCFepFMgodlAoAmw