Chapter 6 - Electronic Structure of Atoms - Exercises - Page 248: 6.4a

There are longer wavelengths at cooler temperatures and shorter wavelengths at hotter temperatures.

We know that at cooler temperatures the waves emitted have longer wavelengths and there are shorter wavelengths at high temperatures. Thus, at the cooler temperature, the wavelengths are not in the visible region and the the burner emits orange visible light.