Why does light behave like a ray in almost every situation a student meets in a laboratory?

1. The wavelength of light is less than a micron, which is a thousandth of a millimetre. 2. Ray behaviour needs objects several times larger than the wavelength, and almost every object on a laboratory bench is far larger than a micron. 3. So light meets mirrors, lenses and slits of ordinary size as a ray, with only subtle wave effects. 4. A wavelength of a centimetre or a metre would put everyday objects below the wave threshold, which is not what is observed. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.1 The Ray Aspect of Light_