why do we use white paper and black pen ?

[didi]

White letters in a black paper, if the all books and news paper are like this would it be easier for us to read or opposite? I think it is definitely very tiring to read.
Why is that?
Black colour reflects very little light but we read the white part.
Are our pupil open wider when the background is black even though the atmosphere is bright?
Anyone has any good answer?

[Fu-Kwun Hwang]

We can read white character on black paper easily. I think our eye will get used to it whatever was provided.

It is just more difficult to make black paper (which absorpt all the light).

[sunilbalani]

white colour is a good reflector while black a good absorber. This provides a better contrast.A black sheet in white lit room is certainly more conspicuous than a white sheet in dark room.