Death is a discrete phenomenon. It is a creature of units. Vegetation relies on sunlight for life. A plant can die, however, only because it is a unit of vegetation. When the amount of light falls from 3.481 to 2.377 on some scale, there is death only because each plant requires a minimum of 0.05 of light, or 0.3, or 0.4.
So, why? Why this discreteness?