The range of the spectrum in which heat is radiated mostly lies within the infrared portion. 辐射热的光谱段大部分落在红外区。
At infrared wavelenths the region is less opaque, and cool protostars are expected to emit most of their energy in the infrared. 在红外波长范围,暗云区是较透明的,而冷的原恒星应在红外区发射其能量的大部分。