Dagaz makes an environment sympathetic to humans. Day is when we do most of what we do. The light of Dagaz is external. Kenaz and Ingwaz are runes with an internal light, as it were. Dagaz shows things for what they are.
Day shines over the whole world.
Dagaz tends to effect an extended area. Kenaz is best to use when you wish to cast light on what is in yourself. Dagaz will shed light on your surroundings.