Introduction

When light with wavelengths between 400 nanometres and 500 nanometres is directed at the retina at high intensity for an extended period, the resulting photochemical processes cause irreversible damage to the retina. LED luminaires emit light within this wavelength range (light at other wavelengths causes damage to human tissue such as the cornea, lens, and skin). Photobiological testing enables LED luminaire manufacturers to assess the safety of LED luminaires and systems. The lighting industry has corresponding standards to restrict this portion of light, such as EN 62471 or IEC 62471 or ANSI/IESNA RP-27. ANSI/IESNA RP-27 (More about ANSI/IESNA) is the original photobiological safety standard for luminaire systems in the United States, which we shall not cover here. The IEC 62471 standard specifies exposure limits, measurement techniques, and a classification scheme for assessing and controlling photobiological hazards from all optical radiation sources, including LEDs. Various biological hazards are considered, encompassing effects on both the eyes and skin. Testing for potential photobiological risks enables luminaire manufacturers to evaluate their products, thereby providing purchasers with greater assurance of product safety.

Classification of photobiological hazards

Photobiological hazards, as defined by IEC/EN 62471, are categorized into numerous classes, including Actinic UV skin and eye, UVA Eye, Retinal Blue-Light, Retinal Blue-Light Small Source, Retinal Thermal, Retinal Thermal – Weak Visual Stimulus, Infrared Radiation Eye, and Thermal Skin, amongst others. The requirements for each category are detailed below.

Actinic UV hazard for the skin and eye

For unprotected skin or eye exposure to ultraviolet radiation, the limit applies to exposure occurring within any 8-hour period. Exposure exceeding 8 hours in any single day need not be considered. The limit for effective radiation exposure is 30 J/m². According to the formula, we know that energy density (J/m²) = irradiance (W/m²) × exposure time (s). Therefore, whether radiation exceeds the limit value is related to the duration of exposure. To prevent damage to the eyes or skin caused by ultraviolet radiation from broadband light sources, the effective spectral irradiance (Es) of the light source must not exceed the corresponding level. The permissible exposure time for each Risk Group decreases as the Risk Group classification number increases

Near-UV hazard for the eye

According to IEC 62471, for ultraviolet A (UVA) radiation in the wavelength range of 315 to 400 nanometres, the near-ultraviolet hazard assessment for the eye requires calculation of the weighted irradiance (Euva) using the eye’s UVA spectral response weighting function as specified in the standard. When exposure duration is less than 1000 seconds, the total radiation received by the eye must not exceed 10,000 joules per square metre. Different Risk Groups have distinct requirements for irradiance levels, with corresponding variations in permissible exposure times. Higher Risk Group classifications correspond to shorter permissible safe exposure durations.

Retinal blue light hazard for retina(L_B and E_B)

To prevent photochemical damage to the retina caused by prolonged blue light exposure (What’s blue light and how to reduce it?), IEC 62471 introduces two concepts (two damage mechanisms): the Retinal blue light hazard exposure limit and the Retinal blue light hazard exposure limit – small source. The Retinal blue light hazard exposure limit is the overarching concept, while the small source represents a sub-scenario assessment method within it. This approach aligns with the actual damage mechanism based on the size of the light source’s image on the retina (field of view angle). When the field of view angle is ≥0.011 rad, the exposure limit refers to the Retinal blue light hazard exposure limit. Conversely, when the field of view angle is <0.011 rad, the source is classified as a small source, necessitating reference to the latter limit. The field of view angle is calculated based on the diameter d of the LED chip/luminaire’s light-emitting surface and the distance l between the human eye and the LED chip (More about LED chips). In practical applications, testing bodies for ZGSM luminaires only determine the exposure limit for the first scenario and ultimately assign the Risk Group. Large light sources exhibit relatively uniform energy distribution, making luminous intensity (L_B) a more appropriate assessment metric. Small light sources, however, form high-energy-density spots on the retina, posing a greater risk of localized damage; thus, irradiance (E_B) is the preferred assessment metric.

Retinal Thermal and Retinal Thermal weak visual for retina

Retinal Thermal and Retinal Thermal weak visual are both assessment items for retinal thermal damage specified in the IEC 62471 standard. The imaging properties of the eye cause incident light to converge upon the retina, significantly increasing energy density. Should a light source possess sufficiently high luminance (Luminance vs illuminance), brief exposure (typically under 0.25 seconds, corresponding to the human blink reflex duration) may cause retinal photoreceptor cells to sustain thermal burns or even necrosis. The core distinction between the two lies in the ‘visual stimulus intensity’: Retinal Thermal covers the full 380-1400nm spectrum, where corresponding light sources (such as high-brightness LEDs or laser pointers) present a pronounced visual stimulus. This triggers protective reflexes in the human eye, such as blinking or averted gaze, and assesses the risk of short-term thermal burns from direct exposure to such light sources. Retinal Thermal weak visual, however, focuses on the 780-1400nm near-infrared band in practical engineering applications. Sources within this range (such as infrared fill lights) present extremely weak or even invisible visual stimulation, making it difficult to trigger protective reflexes. This category assesses the risk of long-term thermal burns from such ‘invisible light sources to the human eye’. The standard determines a light source’s Retinal Thermal hazard classification (Exempt, Class 1, Class 2, or Class 3 hazard) by calculating the corresponding retinal thermal hazard weighted luminous intensity (L_R or L_IR) and comparing it against exposure time thresholds.

Infrared radiation hazard for the eye

The exposure limit for infrared radiation hazards to the eye primarily addresses the harm posed to human eyes by the 780nm-3000nm infrared spectrum. Prolonged or high-intensity exposure to infrared radiation within this band can cause thermal damage to ocular tissues such as the cornea, lens, and retina, potentially leading to corneal burns and cataracts in severe cases. Consequently, the EN 62471 standard establishes exposure limits for the eye to infrared radiation (E_IR) within the wavelength range of 780 nanometres to 3000 nanometres for durations less than 1000 seconds.

Thermal hazard for the skin

The thermal hazard exposure limit for skin pertains to the 380nm–3000nm light radiation spectrum. When light radiation within this spectrum strikes skin tissue, it causes tissue temperature to rise; excessive radiation may result in thermal injuries such as skin burns. The IEC 62471 standard applies solely to small-area exposure. For large-area exposure, due to its involvement with heat exchange, human activity states, and other influencing factors, no provisions have been established. Visible and infrared radiant exposure (380 nm to 3000 nm) of the skin shall be limited to: 20000/t^0.75.

Photobiological hazard exposure limits as per IEC 62471

The IEC 62471 standard specifies the photobiological exposure limits that lighting products must comply with, covering actinic UV hazard, near-UV hazard, retinal blue light hazard, retinal thermal hazard, infrared radiation hazard, and thermal hazard for the skin. These limits are determined based on the wavelength range (200-3000 nanometers), exposure duration (from seconds to 8 hours), and product category, and are designed to prevent acute or chronic damage to the human outer body (skin, cornea, and lens) and inner body parts (retina) from lighting products. These limits are the core standards for product safety classification and compliance testing, ensuring that LED lighting fixtures meet the requirements of IEC 62471 before entering the market. The limits for each type of hazard are explained below.

Actinic UV hazard exposure limit for the skin and eye  

When the exposure time is less than 30,000 seconds (8 hours), the limit for effective radiation exposure is 30 J/m². For example, Risk Group 0 requires a radiation irradiance of <0.001 W/m², with a corresponding exposure time not exceeding 30,000 seconds; Risk Group 1 requires a radiation irradiance of <0.003 W/m², with a corresponding exposure time not exceeding 10,000 seconds; and Risk Group 2 requires a radiation irradiance of <0.03 W/m², with a corresponding exposure time not exceeding 1,000 seconds.

Near-UV hazard exposure limit for the eye

When the exposure time is less than 1000 seconds, the total radiation received by the eyes must not exceed 10,000 joules/square meter. For example, Risk Group 0 requires a radiant irradiance of <10 W/m², with a corresponding exposure time not exceeding 1000 seconds; Risk Group 1 requires a radiant irradiance of <33 W/m², with a corresponding exposure time not exceeding 300 seconds; and Risk Group 2 requires a radiant irradiance of <100 W/m², with a corresponding exposure time not exceeding 100 seconds.

Retinal blue light hazard exposure limit (L_B and E_B)

The limit for retinal blue light hazard is 1,000,000 J/m²/sr. For example, Risk Group 0 requires a radiance of <100 W/m²/sr, with a corresponding exposure time not exceeding 10,000 seconds; Risk Group 1 requires a radiance of <10,000 W/m²/sr, with a corresponding exposure time not exceeding 100 seconds; and Risk Group 2 requires a radiance of <4,000,000 W/m²/sr, with a corresponding exposure time not exceeding 0.25 seconds. For small light sources, the limit is 100 J/m², which generally applies to LED light sources (LED vs other light sources); ZGSM products are not affected by this, so further explanation is not provided.

Retinal Thermal and Retinal Thermal weak visual

The retinal thermal hazard exposure limit is 50000/α/t^0.25. The exposure time for different Risk Groups shall not exceed 10 s for Risk Group 0 or 1, and 0.25 s for Risk Group 2. The corresponding irradiance requirements are 28000/α, 28000/α, and 71000/α, respectively. For different Risk Groups, the retinal thermal hazard exposure limit for weak visual stimuli is 6000/α, with exposure times required to be <1000 s for group 0, 100 s for group 1, and 10 s for group 2.

Infrared radiation hazard exposure limits for the eye

The dangerous exposure limit for the eyes to infrared radiation is required to be <18000/t^0.75. For example, for Risk Group 0, the required irradiance is <100 W/m², with a corresponding exposure time not exceeding 1000 s; for Risk Group 1, the required irradiance is <570 W/m², with a corresponding exposure time not exceeding 100 s; and for Risk Group 2, the required irradiance is <3200 W/m², with a corresponding exposure time not exceeding 10 s.

Table for photobiological hazard exposure limits

Risk Group classification of ZGSM LED lights

To prevent photobiological hazards, the EN 62471:2006 standard specifies relevant measurement procedures and classifies potential risks into four Risk Groups (RG): Risk Group 0 (exempt group), Risk Group 1 (low Risk Group), Risk Group 2 (moderate Risk Group), and Risk Group 3 (high Risk Group). Following classification of LED luminaires (ZGSM LED luminaires) into Risk Groups based on their potential photobiological hazard, these groups determine the safe operating conditions for specific luminaires and the safety distances that must be maintained where applicable. If a tested luminaire is classified within the exempt group or low-Risk Group (Risk Group 1), no detailed workplace assessment is required as no photobiological safety hazard exists. In accordance with ANSI/IESNA RP-27.3. ‘Photobiological Safety for Lamps and Lamp Systems – Risk Group Classification and Labelling’ and 62471-6, these standards also specify labelling requirements for corresponding products. For low-risk products (RG0, RG1), conspicuous warning labels are generally unnecessary beyond standard specifications. Conversely, RG2/RG3 products feature explicit warning notices, usage instructions, and occasionally installation restrictions (e.g., projectors and UV curing lamps).

IEC 62471 test results of ZGSM LED lights

The following presents the IEC 62471 test reports for ZGSM’s 9 series of street lamps (ZGSM street lamps). At a third-party laboratory, testing was conducted on the ST17 series with a maximum wattage of 260W, highest colour temperature of 6500K, and 3030 LED chips. The results indicate: Es = 2.31×10^-9 W/m², Euva =7.41×10^-5 W/m², L_B = 70.6W/m²/sr, E_B (not tested), L_R = 1.5×10³ W/m²/sr, L_IR = 0.218 W/m²/sr, and E_IR was 1.99×10^-3 W/m². Consulting the table reveals all results fall below the Risk Group 0 threshold, thus classifying them as Risk Group 0. Similarly, testing of the 5050 LED chips confirmed the product’s photobiological safety also falls within Risk Group 0. As other series of street lamps possess wattages less than or equal to the Rifle series, all 9 series street lamps ultimately belong to Risk Group 0. Test results for ZGSM urban lights indicate these are classified into Risk Group 0. However, sports field lights were categorized as Risk Group 2 due to excessive wattage causing L_B results exceeding 10,000 W/m²/sr. Furthermore, Risk Group classification may vary if products feature lower wattage, lower colour temperature (About CCT and tunable white lighting) LEDs to reduce blue light, or customized amber lenses.

ZGSM LED lights

Summary

In accordance with the international standard IEC 62471, the photobiological safety of LED light sources requires a systematic assessment of potential hazards to the skin and eyes (particularly the retina) based on their spectral radiation. The standard rigorously specifies exposure limits for various hazards across the ultraviolet to infrared spectrum (200–3000 nm), including ultraviolet photochemical hazards, retinal blue light hazards (classified as L_B and E_B), retinal thermal hazards (including scenarios with low visual stimulation), and infrared radiation with skin thermal hazards. Based on measurement results, products are categorized into four Risk Groups (RG0 to RG3) to define their safe usage conditions. Taking ZGSM brand LED luminaires as an example, third-party testing indicates that key parameters for multiple series of street lamps and urban lights—such as effective ultraviolet irradiance (Es), near-ultraviolet weighted irradiance (Euva), blue light weighted luminance (L_B), are significantly below the exemption group (RG0) limits stipulated by the standard. Consequently, they are categorised as Risk Group 0 (Exemption Group), posing minimal photobiological hazards to eyes and skin under normal usage conditions. However, for certain high-brightness, high-power products (such as sports field lighting), blue light radiation levels may reach Risk Group 2 (Medium Risk Group). Direct viewing of such luminaires at close range poses significant safety hazards and warrants particular caution. For further details, please contact ZGSM.

Related Products

Related Blogs

Related Cases

People also ask

Author introduction