The bug

When use a hoe on a dirt, light level will be down. Therefore, when I use a hoe on a dirt at light level 7, no crops will be planted there.

For the purposes of most game logic, the light level of the block itself is equal to the maximum light level of any of the blocks directly beside or above it. As a result, if these blocks are lit from the top or sides, they are typically one level brighter than a transparent block would be at the same location.