In both high-spin and low-spin complexes, electrons in the t level can absorb photons of light and jump to the upper e level. We can measure the value of the splitting energy, A, from the absorption spectrum of a complex, or we can get a rough idea of relative splittings from color alone. In the table above are listed several octahedral complexes of , along with their main absorption wavelengths and colors. Knowing the relationship between color and energy in these and similar complexes, we can rank the various ligands for effectiveness in producing splitting in the d energy levels:

> en > > , , > > >

This list varies somewhat from one transition metal to another, but generally a more intense, concentrated packet of negative charge on a ligand causes a larger crystal-field splitting than does a large, diffuse cloud of negative density. For example, a localized lone electron pair on a nitrogen atom in ethylenediamine or ammonia is more effective than the diffuse negative charge on a bromide ion.