noun
reflectance; reflectivity
Technical term used in physics, optics, and engineering to describe the fraction of incident light or radiation reflected by a surface.
この塗料は反射率が高いので、夏の暑さを軽減できます。
This paint has high reflectance, so it can reduce summer heat.
鏡の反射率はほぼ100パーセントに近い。
The reflectance of a mirror is close to nearly 100 percent.
透過率 is transmittance, the fraction of light that passes through a material, in contrast to reflectance.
Compound of 反射 (reflection) + 率 (rate, ratio). A straightforward technical term formed from standard Sino-Japanese elements.