The canopy microclimate at the outside of the canopy is obviously affected by the macroclimate and mesoclimate, but that within the canopy depends on the way the canopy itself alters the climate. Bright sunlight falling on a dense canopy with few gaps in California’s Napa Valley may be considered as an example. Suppose a leaf facing the sun at midday receives 100 relative units of sunlight. The second leaf in the canopy will receive less than ten units and the third will receive less than one. So the second leaf in the canopy has a light climate like that of a northern European vineyard on an overcast day. In other words, the number of layers of leaves in the canopy can have even more effect on canopy microclimate than can vineyard location. This drastic reduction in sunlight levels in the canopy is caused by the vine leaves absorbing and reflecting more than 90% of light falling on the upper surface; less than 10% penetrates through to the lower surface.