Lens materials
Refractive index
Optical glossaryLens materials
How strongly a material bends light. Higher index means less material for the same power — a thinner lens.
Estimated edge-thickness reduction
- 1.50
Standard referenceStandard 1.50 material
- 1.56
Up to 10% thinnerthan 1.50 at −6.00, indicative
- 1.60
Up to 20% thinnerthan 1.50 at −6.00, indicative
- 1.67
Up to 30% thinnerthan 1.50 at −6.00, indicative
- 1.74
Up to 40% thinnerthan 1.50 at −6.00, indicative
- Index 1.50: Standard reference
- Index 1.56: Up to 10% thinner
- Index 1.60: Up to 20% thinner
- Index 1.67: Up to 30% thinner
- Index 1.74: Up to 40% thinner
Relative comparison · indicative percentages against 1.50, not measurements
In more depth
The refractive index is how much a material slows light: in a 1.50 material, light travels at two-thirds of its speed in air. The more it slows, the more it bends at a curved surface, so a higher-index lens needs less curvature — and less material — to reach the same power.
The saving is proportional to how far the index is above 1: the curve depth scales with 1 ÷ (n − 1). A higher index also reflects more light from each bare surface and usually disperses color more, so thinness is always a trade rather than a free upgrade.
Across the CLIFF index range
| Index | Material | Curve depth | Reflection | Abbe |
|---|---|---|---|---|
| 1.50 | CR-39 | 100% | 4.0% | 58 |
| 1.56 | — | 89% | 4.8% | — |
| 1.60 | MR-8 | 83% | 5.3% | 41–42 |
| 1.67 | MR-7 / MR-10 | 75% | 6.3% | 31–32 |
| 1.74 | MR-174 | 68% | 7.3% | 32–33 |
Curve depth is relative to a 1.50 lens of the same power, and reflection is for one bare, uncoated surface — both calculated from the index itself. Material and Abbe number are the material manufacturers' published figures, not CLIFF measurements.