gram is usually used to measure light weight object
aluminum is light_weight. gram_atom is metric_weight_unit. gram_atom is not metric_weight_unit. gram is not metric_weight_unit. gram_molecule is metric_weight_unit. luminance_unit is light_unit. luminance_unit is not light_unit. gram_molecule is not metric_weight_unit. gram is metric_weight_unit. lightness is weight.