The photochromic effect in erbium-doped tellurite glass at 479 nm is strongly influenced by the erbium-ion concentration and the presence of other rare-earth oxides. The effect is substantially more pronounced and has a shorter half-life in silicate glasses at erbium-ion concentrations below 1.4*10²¹ cm^-3. The exponential dependence of the lifetime on erbium-ion concentration is compared with that for silicate glasses. The effect in tellurite glass can be enhanced by the addition of 2-4 wt.% ytterbium oxide.