Along with other factors, different output levels also effect the tone of a pickup. The higher the inductance, the warmer the tone becomes and the greater the volume. Lower inductance pickups of similar design tend to be brighter with lower volume. This is why a lower inductance pickup is often used in the neck position with a higher inductance pickup in the bridge position to balance things out. String vibration at the neck is greater and results in a warmer tone and greater volume and the converse is true for string vibration near the bridge.
.21H (Henry) inductance
4K (kiloohms) DC resistance
.33H (Henry) inductance
5K (kiloohms) DC resistance
.52H (Henry) inductance