英语听力文摘 English Digest 529、夜视为何看不见颜色？

 　　Night Vision And Humans: Why Can’t We See Color?

 

　　When we are in a fairly dark room, or outside at night away from lights, we can still see, but we can’t see the colors of things very well. Why is that?

 

　　There are two kinds of light-sensitive organs located in the backs of our eyes: rod-shaped and cone-shaped. Both rods and cones¹ are sensitive to light. The difference between them is that the rods allow us to see in very dim light but don’t permit detection of color, while the cones let us see color but they don’t work in dim light.

 

　　When it gets dark the cones lose their ability to respond to light. The rods continue to respond to available light, but since they cannot see color, so to speak, everything appears to be various shades of black and white and gray.

 

　　A curious thing is that in dim light you can see more clearly out of the side of your eye, because the light-sensitive rods are more highly concentrated off to the side in the back of your eye.

 

　　So, next time you’re out on a clear night, notice how little color you can see, and how you can see objects like dim stars better out of the corner of your eye than from the center.

1 cones   

n.（人眼）圆锥细胞；圆锥体( cone的名词复数 )；球果；圆锥形东西；（盛冰淇淋的）锥形蛋卷筒

参考例句：

• In the pines squirrels commonly chew off and drop entire cones. 松树上的松鼠通常咬掉和弄落整个球果。 来自辞典例句
• Many children would rather eat ice cream from cones than from dishes. 许多小孩喜欢吃蛋卷冰淇淋胜过盘装冰淇淋。 来自辞典例句