  In gravitational lensing, the concept of optical depth assumes the lens is
dark. Several microlensing detections have now been made where the lens may be
bright. Relations are developed between apparent and absolute optical depth in
the regime of the apparent and absolute brightness of the lens. An apparent
optical depth through bright lenses is always less than the true, absolute
optical depth. The greater the intrinsic brightness of the lens, the more
likely it will be found nearer the source.
