Only passes light at 720nm (high-red) and above. Gives more predictable results than filters that only pass Infrared light above 850 or 900nm. Blocks visible light up to 720nm (high-red). Infrared light starts in the high-red area of the visible spectrum at around 750nm and goes up beyond 1000nm.
Very good product, classic packaging for Hoya. Works well for the infrared photo, previously I ordered elsewhere a cheap filter ... and that did not work (a simple red glass!).