Complex sentence: An unusual scene with a preponderance of light colors or specular highlights would have a higher reflectance; a reflected-light meter taking a reading would incorrectly compensate for the difference in reflectance and lead to underexposure.
Split into simpler sentences: An unusual scene with a preponderance of light colors or specular highlights would have a higher reflectance. A reflective meter taking a reading would incorrectly compensate for the difference in reflectance and lead to underexposure.