Objects or surfaces are usually observed or inspected by the human eye, or with a camera by means of light reflected from the object, either from the day or night-time sky or from a light bulb or other manmade light source. However, if an object or surface becomes hot enough to be incandescent, we are strongly tempted to make observations using light emitted directly from the object or surface itself. Unfortunately, we can not always observe the detail on such surfaces that we could otherwise be able to see by using reflected light after the surface has cooled. This article discusses the merits of using reflected light to observe - no matter what the temperature of the area of under observation - and suggests avoiding the temptation to observe hot material by means of the incandescent light.
