'Correct exposure' is what we have when a photograph looks right-not too dark and dense, not washed out, pale and grey-and the details look bright and clear. But correct exposure is almost always a compromise. Films can handle only a limited range of brightness, which is why the best results are obtained in hazy lightning rather than in harsh sunlight. There are frequent occasions when a photographer must decide whether to expose for the highlights or for the shadows. When there is even lighting from all over the scene the problem of which part to expose for does not arise. The range of contrast falls within that which film can handle, so that highlights and shadows alike are full of detail. The better we understand light the more accurately can we visualize how our finished picture will look. Severe underexposure, for instance, will cause dense black in our pictures. We might get this when photographing a cottage in sunshine with the door open: the interior will be very dark. The blackness is caused by absence, or insufficiency, of light beyond the open door. And even though our eye may perceive details inside, if nothing is bright enough to record on our film everything beyond the door will go black.