Deficiency of cones causes colour-blindness while deficiency of rods causes night-blindness.

Explanation

### Step-by-Step Solution:

1. **Understanding Photoreceptors**:
- The human retina contains two types of photoreceptor cells: cones and rods.
- Cones are responsible for color vision and function best in bright light conditions.
- Rods are responsible for vision in low-light conditions and do not detect color.

2. **Deficiency of Cones**:
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