Periods are a normal phenomenon in women which are of reproductive age. In fact it is a sign of adulthood in women. The length of periods varies from women to women. It also depends on the age of women. However, the average length is considered to be from 4-9 days. Anything less than that or exceeding that is considered as irregular.
As far as your condition is concerned, your periods lasts for 8 days, which is completely normal. They are light in the beginning and then get heavy which is also very normal as most of the women start off with light bleeding which gets heavier on day 2 or day 3.