1.   Both types of bird nest deep in caves where little or no light penetrates, and both navigate through the blackness using echoes from their own vocal clicks.

2.   Because the light penetrates into the tissue, it can be used to assess cells at a deeper layer, where abnormalities show up sooner.

3.   Cerus uses a different chemical for red blood cells because light cannot penetrate these cells to activate a psoralen.

4.   Dormers and transoms everywhere insure that natural light penetrates every nook and cranny.

5.   Like Munch, Bergstad is obsessed with deathbed and sickroom scenes, which light cannot penetrate even through there are large windows in the rooms.

6.   Little natural light penetrates to the bottom, so their visibility is limited to a few feet.

7.   Many hydrothermal vents, however, are so deep in the ocean that no light can penetrate.

8.   Prune the tops so that light can penetrate to the bottom of the shrubs, which will stimulate new growth.

9.   Spacing the scaffolds opens up the tree so light can penetrate, which encourages fruit production.

10.   Some people love the cleared-ground stage, when a new prospect suddenly opens and light penetrates the neighborhood from forgotten angles.