One lamp. A clearer understanding of form.
A simple planar-head exercise for seeing the difference between a change of plane and a change of value.
For your deskA planar head, one desk lamp, plain paper and a pencil.
Give the light one clear direction
Place the head on a stable surface near eye level. Start with your lamp above and to one side. Reduce competing room light enough to see a clear shadow, while keeping your drawing area comfortable to work in. A plain background makes the silhouette easier to read.
Choose a view where you can see both the front and side of the face. Adjust the lamp until some planes face the light and others turn away. Keep the setup still for your first study; changing the lamp halfway through makes comparisons harder.
Start with two groups
Draw a small outline of the whole head. Look for the broad shapes of light and shadow before you draw individual facial features. Leave the light group as bare paper and give the shadow group one even tone.
Compare the shadow beneath the nose with the shadows around the cheek and jaw. Notice which edges belong to the model itself and which belong to a shadow falling across it. You do not need to draw every visible ridge.
Let neighbouring planes tell you what to draw
Choose two adjacent planes on the forehead or cheek. Is one noticeably lighter than the other, or are their values close? A physical edge does not always need a dark outline. Make the difference in your drawing as strong or as subtle as it appears in the setup.
Add a middle tone only after the two large groups feel convincing. Keep checking the whole head so that a small feature does not become darker or more detailed than it needs to be.
Change one thing, then compare
Move the lamp to the opposite side and begin a new thumbnail. Keep the first drawing beside it. The head has the same geometry, but the pattern of light is different. Write one sentence below each drawing about what the light helped you see.
The aim is a useful observation, not a polished portrait. Finish by choosing one passage to revisit in a longer drawing: the brow, the cheek, or the turn beneath the jaw.