HWB720 is a "cut-off type - infrared transmission, visible absorption" colored optical glass, made from black glass, achieving a steep transition at ≈720 nm: it absorbs over 99.9% of visible light in the 380–700 nm range, with transmittance rapidly increasing from 720 nm, reaching over 80% at 740 nm, and maintaining stable transmission of ≥90% in the 850-2500 nm band, peaking at approximately 92%. Typical specifications include Φ25 mm×2 mm, with dimensional/thickness tolerances of ±0.1 mm / ±0.05 mm, surface quality 60/40, surface accuracy λ/2, and advantages such as low fluorescence, low reflection, resistance to thermal shock, and long-term color stability. It is often fabricated into filters embedded in security surveillance systems, LiDAR, infrared imaging, fiber optic communications, night vision devices, infrared photography, and various spectral testing equipment, used to block visible stray light, improve signal-to-noise ratio, protect sensors, and enhance infrared imaging contrast.