A light-emitting diode (LED) is a semiconductor assembly that emits light when an electrical current is passed through it. LEDs emit high-intensity optical radiation across the ultraviolet, visible, and infrared (IR) spectrums. “White” LEDs, now commonly available, are rapidly replacing incandescent and fluorescent lighting for conventional lighting. They are more energy efficient and require less maintenance than the incandescent and fluorescent lighting products they replace.
LEDs are commonly used for indicator lights, electronic signs, clock displays, and flashlights. LEDs are also found in ultraviolet (UV) nail curing devices, sold for both salon and home use. In addition, UV-emitting LEDs are now being used in the forensic, photolithography, curing, disinfection, water purification, and medical device industries (including dentistry), and in germicidal and infection control.
Types of LEDs
Listed below are some common types of LED s:
- Surface-emitting (large area) LEDs (SLEDs)
- Edge-emitting LEDs
- Organic LEDs (OLEDs), used mainly in digital displays (e.g., televisions)
SLEDs are the conventional LEDs that have existed for decades. They consist of a chip of semiconducting material doped with impurities to create a p-n junction. Common semiconductors used in the construction of LEDs include gallium, silicon, indium, nitride, and synthetic sapphire. The emission surface of an LED chip is normally on the order of a square millimeter, and when magnified appears as a large disc or square area of high brightness. In addition to being sold as single-chip designs, LEDs are now commonly packaged in arrays, allowing even more light to be produced.
Edge-emitting LEDs have a device structure different from that of the surface-emitting LED. The beam spread is generally smaller for an edge-emitting LED than for a SLED. In addition, the spectral bandwidth of edge-emitting LEDs is slightly narrower than that of a SLED. Typical dimensions of the emitting stripe are 3 mm ´ 100 mm, with an active region several hundred microns long. Because of the high radiances achieved at the emitting facet, it is easier to launch the light into an optical fiber. The radiance of edge-emitting LEDs is orders of magnitude higher than SLEDs.
OLEDs are made by placing a series of organic thin films between two conductors. They are manufactured on flexible plastic substrates and do not require a backlight, making them thinner and more efficient than liquid crystal displays (which do require a backlight). They are often used in mobile phone displays, television screens/monitors, and in the automotive industry.
Health Effects
The increased availability of UV-emitting, white, and extremely bright LEDs has led to some health concern. The eyes and skin are the organs most susceptible to tissue damage from optical radiation. Common effects to both eyes and skin are summarized in the table below. The type of effect, injury thresholds, and damage mechanisms vary significantly with wavelength. The effects may overlap and must be evaluated independently.
Damage from Optical Radiation | |
Eyes | UV photochemical injury to the cornea (photokeratitis), conjunctiva (photoconjunctivitis), and lens (cataracts) of the eye (180–400 nanometers [nm]) |
Thermal injury to the retina (380–1,400 nm) | |
Blue-light photochemical injury to the retina (400–550 nm, unless the eye lacks a natural crystalline lens, also known as ”aphakic,” then 300–550 nm) | |
IR thermal hazards to the lens, such as cataracts (approximately 800–3,000 nm) | |
Thermal injury (burns) to the cornea (approximately 1,400 nm–1 mm) | |
Thermal injury to the cornea (180 nm–1 mm) from high irradiances or lengthy exposures | |
Skin | Thermal damage, burns (180 nm–1 mm) from high irradiances, lengthy exposure, or high temperature of outer lamp casings |
Damage by photosensitization less than 380 nm, which can extend to approximately 700 nm, possibly as a side effect of certain medications | |
Photoallergic reactions in which an antigen, activated by exposure to optical radiation, causes an immune reaction | |
Risk of skin cancer, for which UV radiation (but not visible radiation) is the primary known environmental risk factor |
LED Emission – Health Effects on the Eye
Unless it is a UV-emitting LED, an LED should not be expected to contribute to injuries such as photokeratitis, photoconjunctivitis, and cataracts. Thermal damage (thermal retinopathy) appears with short time exposure to a very high irradiance level. The exposure levels needed to produce thermal damage on the retina cannot be reached with light emitted by LEDs of current technologies.
Traditional LEDs are generally considered safe, with no need for separate LED safety standards, as opposed to the higher-power laser diodes, which are known to cause eye hazards. LED exposures are regulated by the lamps standard (IEC/EN 62471, Photobiological Safety of Lamps and Lamp Systems). Based on current exposure limits in this standard, most visible LEDs and infrared LEDs (IREDs)—particularly SLEDs—pose no acute hazard to the eye. However, some specialty lighting products (e.g., stage lights) could potentially fall into a higher risk group, as defined in current lighting safety standards.
Acute damage to the human retina from typical exposure to blue or white LEDs has not been observed and documented in the literature. The principal retinal hazard resulting from viewing bright light sources is photoretinopathy (e.g., solar retinopathy), with an accompanying scotoma, which can result from staring at the sun. However, the eye is well adapted for the protection against the harmful full-spectrum optical radiation from sunlight. Bright light sources such as the sun, arc lamps, welding arcs, and bright LEDs produce a natural aversion response by the eye. This response limits the duration of exposure to a fraction of a second (typically less than 0.25 s).
Visual Disturbance and Circadian Rhythm Disruption
The only established acute adverse health effects from LEDs are those caused by temporal light modulation (flicker), glare, and circadian rhythm disruption.
Flicker effects
Light sources driven directly from the main power supply are likely to have a degree of temporal light modulation. Most A/C-driven LEDs are subject to flicker effects, regardless of the emission spectrum.
Glare
Glare is a source of indirect hazards, which are not caused by the light itself. For example, in the workplace, glare can cause accidents when it interferes with the safe use of machines and tools. In everyday life, glare can be the cause of vehicular accidents and falls. Glare can also create visual disturbances when LED light fixtures are not properly designed.
- Discomfort glare is produced when a light source has a luminance (brightness) vastly greater than surrounding objects (e.g., an auto headlight on a very dark country road is brighter than the same light viewed in daylight). People complain of discomfort under these types of conditions.
- Disability glare is produced when the luminance of the source is so bright that the scattering of light within the human eye obscures surrounding objects. This type of glare becomes more pronounced in elderly people because of the increasing scatter of the human lens with aging.
Circadian rhythm disruption
The exposure to intense “cool white”/blue-rich radiation can lead to a disruption of the body’s daily circadian rhythm because the peak sensitivity of the eye for circadian rhythm regulation is in the blue (460–470 nm) wavelength region, where most white LEDs have strong emissions. It should be noted that this can happen if the exposure occurs in the evening or nighttime, but not during the day.
There is a growing tendency to use tunable LEDs to influence human behavior and wellness. This could lead to greater exposure to blue/short-wavelength light. Higher correlated color temperature (CCT) (“cool” light) is thought to increase alertness, whereas lower CCT (“warm” light) is expected to induce relaxation/calmness. The CCTs of early LEDs were 6,000 K or higher and were not well accepted by the public because the bluish-white light was described as harsh, with poor color rendering. A warmer CCT of approximately 3,000–4,000 K is more acceptable. For comparison, consider that the CCT of clear daylight is in the range of 6,000–7,000 K, while on a cloudy day, it is in the range of 4,000–5,000 K, and the CCTs of incandescent lamps are around 2,700 K.
Exposure Assessment and Limits
As mentioned above, LEDs are regulated by the lamps standard (IEC/EN 62471, Photobiological Safety of Lamps and Lamp Systems). The standard provides the methods for the classification of lamps into one of four risk groups (RGs), RG0, RG1, RG2, and RG3, which are based on established exposure limits. If a lamp is classified as RG0 (also known as “exempt”), no risk is associated with exposure to it. The risk from exposure to lamps in risk groups above RG0 increases gradually to RG3. The focus of a safety assessment is RG3, which is high risk. Typically, the manufacturer labels LED lamps according to their risk group.
Risk Group | Philosophical Basis |
Group 0 (Exempt) | No photobiological hazard |
Group 1 (Low Risk) | No photobiological hazard under normal behavioral limitations |
Group 2 (Moderate Risk) | Does not pose a hazard due to aversion response to bright light or thermal discomfort |
Group 3 (High Risk) | Hazardous even for momentary exposure |
LEDs have a spectral bandwidth much greater than that of lasers, and because they are not “point sources,” they should be treated as incoherent optical sources. For broadband incoherent sources, several different hazards must be assessed over a range of wavelengths so that limits for the different hazards apply in parallel.
The emission limits are generally derived from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) or the American Conference of Governmental Industrial Hygienists (ACGIH) threshold level values (TLVs) and biological exposure indices (BEIs). Berkeley Lab has adopted the ACGIH guidance for exposure limits to optical radiation. To evaluate the hazard, the exposure to the eyes and skin at the location of exposure is compared with the respective exposure TLVs. The limits are applicable to continuous light sources with a maximum exposure time of eight hours. The limits are based on radiation levels presumed not to create adverse health effects. Compliance with the limits may be demonstrated by several means: generic assessments, theoretical assessments, or measurements. Depending on the source, several measurements with different detectors may have to be taken.
If the results do not exceed the exposure limits, no further assessment is required. If the results exceed the TLV, the maximum exposure time should be calculated. In such cases, the work scope may need to be re-evaluated, and engineering and/or administrative controls must be implemented.
For more information or for a request for evaluation and measurements, contact the subject matter expert for non-ionizing radiation listed on the Non-ionizing Radiation (NIR) home page.
Light and NIR Threshold Limit Values (TLVs)
Exposure Controls
If light hazards have been identified in the workplace, it may be necessary to implement one or more control measures to eliminate exposure or reduce it as far as is reasonably practicable. The hierarchy of controls is described below.
Elimination or Substitution
Careful consideration should be given to whether exposure to the light hazard can be eliminated by altering the process used or whether the light source can be substituted for one that is less harmful. If this is not possible, or if the risk is not sufficiently reduced (e.g., when substituting for a less harmful source), then consider implementing engineering controls.
Engineering Controls
Location
Having LED equipment located in a separate room, alcove, or low-traffic area of a lab is ideal. To help prevent exposure to other employees, avoid placing equipment in the direct vicinity of desk areas or other equipment.
Enclosure
The use of light-tight cabinets and enclosures is the preferred means of preventing exposure. Where it is not practicable to fully enclose the light source, use screens, shields, and barriers. Covers or partial enclosures must not be removed when the equipment is in use. If they are discolored, degraded, or damaged in any way, they should be replaced.
Interlocks
Some equipment comes with interlock devices. Interlocks must not be tampered with. Replace or repair them when defective.
Administrative Controls
Typical administrative controls include limiting access to the high-risk LEDs, ensuring that personnel are aware of the potential hazards, and providing personnel with training and safe working instructions.
Training
Personnel should carefully study the manufacturer’s manuals for the LED equipment and be familiar with its use. The manufacturer’s manuals provide specific safety-related information that must be completely understood before using the equipment. It is important never to deviate from the instructions for safe operation. If any uncertainty or concern exists regarding the safe use of LED equipment, contact the manufacturer for clarification.
At a minimum, lab personnel should be familiar with the following when working with or around LED light:
- Proper use of the LED light-producing equipment
- Warning signs and labels
- Proper use of protective equipment provided by the manufacturer (e.g., shields/enclosures), as well as personal protective equipment (PPE)
- Symptoms of LED exposure
Minimizing exposure
Do not view the LED lamp directly. Although the inverse square law applies to non-laser-beam light radiation, it is not advisable to look directly at any LED source.
Hazard warning signs
The lamp standard requires that LED products be labeled to exhibit the risk group of blue-light hazard when it is classified as RG2 or RG3. Furthermore, for all products in excess of the exempt group (RG0), the manufacturer should provide the following user information:
- A clear statement that the lamp or lamp system exceeds the exempt group exposure limits and the viewer-related risk depends on how the users install and use the product.
- The most restrictive optical radiation hazard and other optical radiation hazards in excess of exempt group (see the table of labeling requirements below).
- Exposure values and the hazard distances with optional graphical presentation of distance-dependent exposure values. Typically, the exposure assessment is performed at a distance of 200 mm.
Hazard | Risk Group 0
(Exempt) |
Risk Group 1 | Risk Group 2 | Risk Group 3 |
Actinic UV | – | NOTICE UV emitted from this product. Minimize exposure to eyes and skin. Use appropriate shielding. |
CAUTION UV emitted from this product. Eye or skin irritation may result from exposure. Use appropriate shielding. |
WARNING UV emitted from this product. Avoid eye and skin exposure to unshielded products. |
UVA | – | NOTICE UV emitted from this product. Minimize exposure to eyes and skin. Use appropriate shielding. |
CAUTION UV emitted from this product. Eye or skin irritation may result from exposure. Use appropriate shielding. |
WARNING UV emitted from this product. Avoid eye and skin exposure to unshielded products. |
Blue-Light Radiance | – | – | CAUTION Possibly hazardous optical radiation emitted from this product. Do not stare at operating lamp. May be harmful to the eye. |
WARNING Possibly hazardous optical radiation emitted from this product. Do not look at operating lamp. Eye injury may result. |
Retinal Thermal Hazard | – | – | CAUTION Possibly hazardous optical radiation emitted from this product. Do not stare at operating lamp. May be harmful to the eye. |
WARNING Possibly hazardous optical radiation emitted from this product. Do not look at operating lamp. Eye injury may result. |
IR Radiation Eyes | NOTICE IR emitted from this product. Use appropriate shielding or eye protection. |
CAUTION IR emitted from this product. Do not stare at operating lamp. |
WARNING IR emitted from this product. Avoid eye exposure. Use appropriate shielding or eye protection. |
|
Retinal Thermal Hazard Weak Visual | WARNING IR emitted from this product. Do not stare at operating lamp. |
CAUTION IR emitted from this product. Do not stare at operating lamp. |
WARNING IR emitted from this product. Do not look at operating lamp. |
Source: IEC 62471-2
In addition to manufacturers’ labels, warning signs are necessary unless the LED radiation is completely enclosed or is in the exempt group. A warning sign must be posted at the entrance to labs or spaces where light exposure exceeds any of the exposure limits.
Examples and variations of the LED hazard warning sign:
Personal Protective Equipment
Depending on the risk assessment, appropriate PPE may include eyewear, face shields, gloves, and lab coats. LED light is very bright, and prolonged exposure may lead to discomfort or even injury and should be avoided.
Eyewear
If viewing intense visible light or blue light cannot be avoided, amber-tinted eyeglasses or goggles should be worn.
Examples of eyeglasses appropriate for protection from intense visible light:
Examples of special safety glasses that are available for LED ranges:
All protective eyewear should provide 100% UV protection.
Use eyewear that is appropriate for the work. For best protection, the eyewear should be compliant with ANSI Z87.1, which requires markings on the eye protection that is provided. Eye protection that is Z87.1-compliant is marked with “Z87.” Additional markings fall into three categories: impact vs. non-impact, splash and dust protection, and optical radiation protection.
Optical radiation protection is a lens’s ability to protect against radiation. This is indicated by a letter designation, which is typically followed by a rating number. The markings are as follows:
- Welding filter: “W” followed by a shade number on a scale from 1.3 to 14
- UV filter: “U” followed by a number on a scale from 2 to 6
- Infrared (heat) filter: “R” followed by a number on a scale from 1.3 to 10
- Visible light (glare) filter: “L” followed by a number on a scale from 1.3 to 10
Face shields
In some cases, where use of high-intensity UV LEDs is required, a face shield may be a good option for protection. Full face shields should be worn in addition to safety glasses or goggles.
Green lenses can absorb a certain amount of UV, visible, and IR light, and these types of lenses are often used in welding operations. The lenses are marked with a shade number that shows the level of protection against hazardous light.
Examples of face shields:
For more information on PPE or to request an evaluation and measurements, contact the subject matter expert for non-ionizing radiation listed on the NIR home page.
References
American Conference of Governmental Industrial Hygienists (ACGIH), 2016. 2016 TLVs and BEIs.
American National Standards Institute/Illumination Engineering Society of North America (ANSI/IESNA), 2015. Photobiological Safety for Lamps and Lamp Systems – General Requirements, ANSI/IESNA RP‑27.1-15.
ANSI/IESNA, 2017. Recommended Practice for Photobiological Safety for Lamps – Risk Group Classification and Labeling, ANSI/IESNA RP-27.3-17.
Haigh, N., 2020. Optical Hazard Assessment in the Ultraviolet Region Using Laser Safety (60825) and Lamp Safety (62471) Guidelines, LIA Today 28 (2): 8–12.
International Commission on Non-Ionizing Radiation Protection (ICNIRP), 2000. ICNIRP Statement on Light-Emitting Diodes (LEDs) and Laser Diodes: Implications for Hazard Assessment, Health Physics 78 (6): 744–752.
ICNIRP, 2004. Guidelines on Limits of Exposure to Ultraviolet Radiation of Wavelengths Between 180 nm and 400 nm (Incoherent Optical Radiation), Health Physics 87 (2): 171–186.
ICNIRP, 2013. ICNIRP Guidelines on Limits of Exposure to Incoherent Visible and Infrared Radiation, Health Physics, 105 (1): 74–96.
ICNIRP, 2020. Light-Emitting Diodes (LEDs): Implications for Safety, Health Physics 118 (5): 549–561.
International Electrotechnical Commission IEC/EN 62471, 2006. Photobiological Safety of Lamps and Lamp Systems.
International Electrotechnical Commission IEC 62471-2, 2009. Photobiological Safety of Lamps and Lamp Systems – Part 2: Guidance on Manufacturing Requirements Relating to Non-laser Optical Radiation Safety.
James, R.H., Landry, R.J., Walker, B.N., and Ilev, I.K., 2017. Evaluation of the Potential Optical Radiation Hazards with LED Lamps Intended for Home Use, Health Physics 112 (2): 11–17.
Schulmeister, K., O’Hagan, J., and Sliney, D.H., 2019. Lamp and LED Safety – Classification vs. Realistic Exposure Analysis, Proceedings of the International Laser Safety Conference, Paper 801.
UL LLC, 2012. Assessing the Photobiological Safety of LEDs, white paper.