The Speeds of Light through different materials

The speed of light in empty space is about 300 million m/s. Light passing through a material such as air, water, or glass, however, travels more slowly than this. This is because the atoms that make up the material interact with the light waves and slow them down. List 1 compares the speed of light in some different materials.

Light travels at different speeds in different materials.

• The speed of light through the air is about 300 million m/s. (3×10⁸ m/s)
• The speed of light through water is about 227 million m/s. (2.27×10⁸ m/s)
• The speed of light through glass is about 197 million m/s. (1.97×10⁸ m/s)
• The speed of light through diamond is about 125 million m/s. (1.25×10⁸ m/s)