Red LED light has several unique features, and consequently several unique applications. Most significantly, red LED light has little or no impact on night vision. Red LED light is also invisible to most insect eyes since they generally see in three specific colors—ultraviolet (UV), blue, and green. With the exception of humans, most mammals also lack the ability to see red light. Because of this, red LED light tends not to attract insects and is unlikely to spook wildlife.
The perception of color begins as light enters the eye and is absorbed by specialized cells located in the retina. These cells respond to light and transmit signals to the brain. The color perceived by the brain is determined by the wavelength of light emitted from or reflected off objects in the world around us. In all mammals, the retina is comprised of light sensitive cells called rods and cones. Rods function in the absence, or near absence, of light and permit night vision. Rods contain rhodopsin, a chemical that absorbs and changes shape when exposed to only a few photons of light. If exposed to a broad spectrum of light, the pigment immediately bleaches, resulting in temporary blindness that lasts approximately 30 minutes. In humans, rhodopsin is less sensitive to longer wavelengths of light; therefore red light slowly depletes the eye’s rhodopsin so night vision is preserved. Rather than affecting the rods in the eye, red light is detected by the cones.
Cones function in full light and permit daytime and color vision. Humans possess blue, green and red cones which allows us to see colors spanning from 400 nm (deep purple) to 750 nm (deep ruby red). By comparison, Insects as well as animals such as deer, elk and bear have no red cones and have great difficulty detecting red LED light. It’s easy to see then (no pun intended), why red LED light is well suited for hunting, military operations and astronomy.
LEDs in general are remarkable for several reasons. An LED is a solid-state device that converts electricity to light with minimal heat generation, therefore they are extremely efficient. The bandwidth of light emitted is very narrow, typically only 5 nm, and the color can range from UV (350 nm) to infrared (700 nm) depending on their chemical composition. An LED will function for tens of thousands of hours if not subjected to electrical overload. Their solid-state design also makes them durable; they are difficult to shatter and rarely need to be replaced.