Applied Innovative Technologies Blog

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.

Green LED light has a variety of unique attributes and benefits. Most high brightness green LEDs emit light centered around 540 nanometers (nm).  This wavelength nearly matches the optimum sensitivity of the human eye in daytime and nighttime conditions.  For the human eye accustomed to daytime light (photopic vision) the maximum efficiency is for light centered at 555 nm.  For the human eye adapted for night vision (scotopic vision), the maximum efficiency is for light centered at 510 nm, which is a wavelength that corresponds to blue-green light.  Because green LEDs so closely match the optimum performance point of the human eye, their light enables objects to be seen with high resolution and in high contrast while having minimal impact on night vision. 

Green LED light also has excellent transmission through water.  The visible wavelength that transmits the furthest through water is 480 nm, which corresponds to a true blue-green.  As a corollary to this, one my think that blue-green light would also transmit the furthest through clouds and fog, since they are comprised of water in vapor form.  Clouds and fog are white however because they uniformly scatter all visible wavelengths ranging from 400 to 750 nm.  One might ask then, why are fog lights yellow?  The answer to this is three fold.  First, longer wavelengths (reds, oranges and yellows) scatter off of water droplets less than shorter wavelengths (purples, blues and greens).  Consequently, less light will be scattered back towards the vehicle’s driver if longer wavelength light is used.  This in turn will minimize the potentially blinding  ”wash out” effect.  Second, as already stated, the human eye is most sensitive to yellow light.   So, the best compromise between eye sensitivity and minimal scattering is yellow light.  Third, sodium vapor lamps are extremely efficient at converting electrical energy into yellow light.  Sodium lamps also have long operational lifetimes, are easy to manufacture and are relatively inexpensive.

Green LED light can also be used to illuminates insects such as scorpions and millipedes.  Though these insects fluoresce green when illuminated with UV light, their exoskeletons reflect green light quite effectively.  Green LED light can also be used to attract many species of fish.  Fish eyes, like human eyes, are extremely sensitive to green light.  Green light scattered off potential food (such as fishing lures), will immediately grab the attention of fish swimming in the area – and because green light travels great distances through water, the area can be quite large.