Have you ever been driving at night—perhaps on a twisty two-lane highway—when the headlights of an oncoming car seemingly “crash” into your retinas? Blue-tinged LED beams leap out from behind a curve, or crest over a hillside, and for an instant it feels like you may have gone blind. Your vision erupts with a painful jolt of white. You squint through patchy discolorations trying to locate the lane lines. A quick flip of your high beams results in an even brighter display from the oncoming car. And now there are two drivers swerving past one another who couldn’t read the top line at the eye doctor.
As nighttime images of the earth from the International Space Station confirm, ours is an increasingly illuminated world. And LEDs, or light emitting diodes, supply a cheap and efficient means for broad illumination, not just for vehicles but increasingly for street lighting. Yet some types of LEDs have recently raised concerns of associated health risks.
In June 2016, the American Medical Association released a report titled “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting.” In a press release accompanying the report, the AMA explained that high intensity “blue-rich LED lighting can decrease visual acuity and safety, resulting in concerns and creating a road hazard.” Additionally, blue-rich LED streetlights operate at wavelengths that suppress melatonin. And “white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps.” Surveys found that such lighting in residential areas was associated with “reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning and obesity.”[i]
A parallel development to LEDs is LASERs. There are key similarities and differences between the two technologies. Both originated in scientific advancements of the 1960s. Both names are acronyms, with the latter referring to Light Amplification by Stimulated Emission of Radiation. And both use diodes to generate distinct forms of light.
Here is where the two technologies diverge. When electricity passes through an LED diode, incoherent visible light is emitted, which spreads in all directions like illumination from traditional electric filament bulbs. But, as described by the Laser Institute of America (LIA), lasers use highly specialized diodes which generate energy “at or near the optical portion of the electromagnetic spectrum.” When this energy is visible to the human eye, we call it “light.” When it is invisible, we call it “radiation,” which is different from the radiation attributed to radioactive materials. The energy from a laser is amplified to extremely high intensities through an atomic process called stimulated emission. The result is a highly directional beam of coherent energy, meaning all the individual energy waves are aligned, “in phase,” and moving in the same direction.[ii] To use an analogy, LED light is like a bumper car ride at an amusement park. LASER energy is like the start of a car race, where a pace car leads orderly rows of vehicles in a straight line.
Each technology has its ideal uses. LEDs illuminate broadly, while LASERs pinpoint, and are best for tasks where focalization and precision are required. Of course, the drama of high-power, visible lasers has long captured the public consciousness and tends to influence perceptions. Currently, there are four laser categorizations, plus sub-categories, based upon safety to humans, identified by the International Electrotechnical Commission and presented in their report “IEC-60825-1: Safety of laser products.”[iii]
In the report, the IEC states that due to the “wide ranges possible for the wavelength, energy content, and pulse characteristics of a laser beam, the hazards arising in its use vary widely.” The result is that the IEC’s categories focus more on the health hazards of human exposure. And the IEC provides a series of tables that guide product classification based upon the combination of pulse duration, “output power(s) and wavelength(s) of the accessible laser radiation over the full range of capability during operation.”
Category 4 includes the highest intensity lasers—those considered either a fire or skin hazard. Such lasers are also deemed diffuse reflection hazards, meaning just the rebound of a pulse off a random surface could be dangerous to humans. These have long been the lasers of science fiction films, such as the famous scene in Goldfinger during which a laser slices across a medical table toward a restrained James Bond.
More recently, such lasers have become reality. In December 2014, the U.S. Navy posted a video to YouTube demonstrating their Laser Weapon System (LaWS). During a series of tests, the 30-kilowatt system, mounted aboard the USS Ponce, disabled an aerial drone and melted a hole in a test boat.[iv]
Category 3 lasers are those which are hazardous to humans if they look directly into the beam with the naked eye for an extended time period. These lasers can emit at any wavelength, according to the LIA, so long as the beam cannot cause diffuse reflection off non-mirror-like objects. These lasers are not considered skin or fire hazards. Because the human blink reflex (1/4 second) is considered sufficient to prevent injury from extended viewing, class III lasers are generally considered safe and remain relatively unregulated by agencies such as the FDA.
Category 2 lasers must be visible to the naked eye. Because of their brightness, looking directly into the beam is often uncomfortable but momentary viewing is generally not hazardous. Meanwhile, intentional extended viewing is considered hazardous.
Laser pointers are the best-known examples of Category 3 lasers, with some being Category 2. The cases of distraction and temporary blindness from malicious laser pointer attacks on airline pilots, sports players, and random individuals is well-documented. Another example of Category 2 lasers are grocery store check-out scanners.
Category 1m lasers are the second-safest type. The one exception, described by the IEC, is if a viewer looks directly into a wide-diameter Category 1m beam using an optical magnification device, such as a telescope or binoculars.
Category 1 includes the safest types of lasers. According to the LIA, “This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any exposure conditions.” In other words, they’re harmless. One example of a Category 1 laser is those in CD-ROM players.
All Velodyne LiDAR sensors, including the HDL-64E, HDL-32E (pictured on left), and the VLP-16 Puck series are categorized as class I laser products. Each sensor has between 16 and 64 lasers, which rapidly rotate at approximately 10 hertz, or 10 full revolutions per second. Meanwhile, each individual laser pulses at a wavelength of 905nm with an average power of 2 milliWatts. For comparison purposes, this is about 1/5,000th or 0.02% of the power output in your standard 10-watt LED headlamp bulb on a low-beam setting.
This means that any single laser beam would sweep across an inadvertently glancing eye in approximately 1 millisecond with an average power less than common laser pointers. And since each individual laser is mounted in a different orientation and angle, multiple lasers cannot strike the eye at once and increase the power. Even if a viewer intentionally stares at a Velodyne sensor, the combination of low power and rapid rotation results in a class I rating. Therefor, the Puck’s roughly 300,000 beam points per second are harmless to the very humans the sensors are designed to protect.
[i] “AMA Adopts Guidance to Reduce Harm from High Intensity Street Lights” American Medical Association. June 14th, 2016
[iii] “IEC-60825-1: Safety of laser products” International Electrotechnical Commission. Edition 1.2, August 2001