Its easy there will be no light on earth and indirectly it will cause the death of people i will explain u  see if there will be no light then plants  will not be able to make photosynthesis and there will be no oxygen and if no oxygen then no human can breathe and if they will not breathe then they will die. 
hope this made u understand!!!!!!!!
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if there is no light(from sun),then there will no heat,temperature will reduce to leads to ICE-AGE !☺so no human can survive for a long ice+darkness
good nirmal nice point
We can't survive since only because of sun light plants can produce carbohydrates if there is no sun light the plants produce carbohydrates during which oxygen is released if this process doesn't occur there will be no oxygen so  we can't survive. And even the heat required for our body is provided by sun. And much more with out sunlight it is impossible to live . so sun light is necessary for our life .
  I hope this would help you 

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