If you are fortunate enough to live in the north woods, then you know that the "Dog Days of Summer" (Wiki) are followed by the Dark Days of Summer. These are the days that our house gets to be quite dark inside even at midday with the sun shining.
The sun is now taking a lower path across the sky so that the sunlight cuts across a wide swath of tree leaves, effectively blocking and scattering much of the light. This will continue and worsen in the weeks to come until the leaves fall.
This darkness does not occur in the Spring as the leaves do not come out until early May and are rather small for a while at that. By that point, we are only a month or so before the solstice and the sun is on a quite high trajectory.