Lens shade number indicates the amount of darkness that provided by it against intense lighting. Lens shade comes with DIN 3-5/8-13 range. DIN stands for Deutsches Institute fur Normung means German institute for standardization. The number after DIN indicates the darkness, higher the number, darker the shade will be. DIN 3 shade used as maximum light shade and DIN 13 used as a maximum dark shade. As more intense the spark light, the darker the shade lens you need to protect your eyes.