Darkness is nothing but the absence of light.
people do not get frightened by darkness, but it is their mind which makes them feel like that.

here is the list of some things that frightens people in the dark
1.their own shadow.
2.a mirror
3.door creaking sound 
4.sudden noise
5.our imagination
6.sudden appearance of family members
7.deadly silence

but the most important thing is our mind 

i hope this helped you    :-)