Jim Brodrick on Optical Safety of LEDs

Republication of Postings from the U.S. Department of Energy (DOE) Solid-State Lighting Program

by Jim Brodrick, U.S. Department of Energy

In two previous Postings and a Technology Fact Sheet, we’ve discussed the possible effects of LED lighting on our biological clocks. But a related question that has spawned a certain amount of confusion and misinformation is how safe LED lighting is for the human eye. To answer it, the U.S. Department of Energy (DOE) has come out with a new Fact Sheet entitled Optical Safety of LEDs, which clarifies what’s known about that issue and takes a look at current standards for photobiological safety.

Because LEDs that are used for general illumination emit neither ultraviolet (UV) nor infrared (IR) radiation, any concerns about the optical hazards of those LEDs are confined to the visible range of the spectrum, which is sandwiched between UV and IR and extends in wavelength from roughly 380 to 780 nm. The main concern that’s been expressed has to do with something called “blue light hazard,” which refers to photochemical damage to the eye’s retina that can result from too much exposure to light in the violet and blue range of the spectrum (between 400 and 500 nm). Blue light hazard is a real phenomenon, but the question is whether white-light LEDs pose any more of a blue light hazard than other types of general-purpose lighting.

The answer, in a nutshell, is “no.” For one thing, light at any given wavelength is the same, regardless of what source it was emitted from or what surface it was reflected off of. In other words, as long as the wavelengths are identical, there’s no physical difference in the light itself, or in the physiological effects of that light — whether it came from an LED or from any other source. This means that blue light from an LED is no different from blue light from an incandescent lamp, a fluorescent tube, a high-intensity discharge lamp, or a CFL.

The question then becomes “Do LEDs emit more blue light than other sources?” Again, the short answer is “no.” All white-light sources emit light over a range of wavelengths rather than just at one wavelength, and it’s even possible for two sources that look identical to have different spectral content. While it’s true that most white-light LED products include a blue LED pump, the proportion of blue light in the spectrum is not significantly higher for LEDs than it is for any other light source at the same correlated color temperature (CCT).

The misconception that LEDs emit more blue light than other sources may be due to several factors. The blue pump results in a spike in the spectral power distribution at short wavelengths — a feature that’s especially noticeable at high CCTs, which were common in the earliest LED products but are less common today. At lower CCTs, this spike may be barely noticeable at all. Although most LED products sold today have CCTs that are similar to their conventional counterparts (2700 K or 3000 K for screw-base lamps, 3500 K or 4000 K for fluorescent-replacement products), it’s possible to create LED products in a wide range of spectral power distributions — unlike standard incandescent lamps, whose spectral power distributions are essentially all the same.

Because blue light is essential for proper visual appearance and color rendering, all white light intended for interior applications — regardless of the type of light source — must have a blue component, just as sunlight has. But the amount of blue light in typical architectural lighting products does not reach hazardous levels, as defined by the International Commission on Illumination (CIE), the International Electrotechnical Commission (IEC), and the American National Standards Institute (ANSI). What’s more, even if the light intensity gets uncomfortably high, the risk for eye damage is mitigated by our bodies’ automatic defense mechanisms — including various aversion responses (blinking, head movement, and pupil constriction) and continuous eye movement, which protect the retina from overexposure. Without these reflexive responses, the sun could damage our eyes.

Although LED products are no more hazardous to the eyes than other lighting technologies that have the same CCT, and white-light products used for general illumination are not considered a risk for blue light hazard according to current international standards, that doesn’t automatically guarantee the optical safety of all light sources. The optical safety of specialty lamps and colored light sources has to be considered on a case-by-case basis, and sources that are used around susceptible populations — such as adults with certain types of eye disease, and infants — require additional evaluation.

You can read more about the topic in Optical Safety of LEDs, which is available–along with other SSL Technology Fact Sheets–at www.ssl.energy.gov/factsheets.html.

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