Do you have to see light for a day to exist?

Answer From The Annual Reading Schedule - Week 15 Notes For Exodus: No. In Exodus 10:22 it states there was darkness for three days. It is not a requirement to see light for a day, or even multiple days, to exist. I bring this question up because some teach that the word Yom (Hebrew word translated "day") only refers to when there is light. However, seeing light is not a requirement. Even if there is no light, a day can still exist and pass in terms of time. Some say that there is no "dark part of a day", but this shows that for three days there was no light part of a day – so there can be a dark part of a day.