Safety

Basics

Infrared (IR) radiation is commonly used in eye-tracking systems to illuminate the eye without being visible to the human eye. While IR radiation is a natural part of our environment (approximately 50% of solar radiation is infrared), prolonged or excessive exposure can be harmful, particularly to sensitive areas like the eyes.

To ensure safe use, guidelines have been established that define exposure limits based on factors such as the affected body part (e.g., eye, skin), the wavelength of the radiation, and the duration of exposure. My safety assessment is primarily based on two authoritative sources:

The ICNIRP (International Commission on Non-Ionizing Radiation Protection) is an independent organization that provides scientifically backed guidelines on the health effects of non-ionizing radiation, including infrared. Their exposure limits are widely recognized and used internationally.

EN 62471 is a European standard that provides detailed criteria for evaluating the photobiological safety of optical radiation sources. It specifies exposure thresholds to prevent thermal and photochemical damage to the eyes and skin.

These sources form the foundation of my calculations, design decisions, and safety precautions, which are designed to keep IR exposure from the system well below the applicable exposure limits. Since the content and limits of both references are essentially identical, only the EN 62471 standard will be explained in detail below. The ICNIRP sources are cited without further elaboration.

EN 62471

EN 62471 evaluates photobiological hazards from optical radiation in the range of 200-3000 nm. In the context of this project, continuous infrared exposure at approximately 860 nm for more than 10 seconds is relevant, specifically involving thermal hazards to the retina, thermal effects on the lens, and thermal damage to the skin.

Infrared radiation hazard exposure limits for the eye

IR radiation can be absorbed by the outer and inner structures of the eye, including the cornea and lens, leading to localized heating. Since IR radiation is invisible and does not trigger natural protective reflexes, the eye is particularly vulnerable to unintentional overexposure. For exposure durations longer than 1000 seconds, EN 62471 sets strict irradiance limits to prevent acute thermal injury and minimize long-term degenerative effects like cataractogenesis:

To avoid thermal injury of the cornea and possible delayed effects upon the lens of the eye (cataractogenesis), ocular exposure to infrared radiation, \(E_{IR}\), over the wavelength range 780 nm to 3000 nm, for times greater than 1000 s, shall not exceed [EN 62471 4.3.7]:

$$E_{IR} = \sum_{780}^{3000} E_{\lambda} \times \Delta \lambda \leq 100 \quad \left[\frac{\text{W}}{\text{m}^2}\right] \quad \text{for } (t > 1000 \text{ s})$$$$E_{IR} \leq 100 \frac{\text{W}}{\text{m}^2} = 10 \frac{\text{mW}}{\text{cm}^2} \quad \text{for } (t > 1000 \text{ s})$$

Where:

• \(E_{\lambda}\) is the spectral irradiance,
• \(\Delta \lambda\) is the bandwidth,
• \(t\) is the exposure duration,
• \(E_{IR}\) is the infrared irradiance (total IR radiation power per unit area over the wavelength range 780-3000 nm).

Retinal thermal hazard exposure limit (weak visual stimulus)

Unlike the general radiation limits that primarily address thermal effects on the front parts of the eye, the retinal thermal hazard exposure limit focuses on the risk of damage to the retina caused by infrared radiation. Even when the visual stimulus is weak or barely noticeable, the radiation can be concentrated onto the retina, causing localized heating and potential injury. Because the retina is particularly sensitive to temperature increases, EN 62471 establishes strict exposure limits for short durations to protect retinal cells from irreversible thermal damage.

For an infrared heat lamp or any near-infrared source where a weak visual stimulus is inadequate to activate the aversion response; the near infrared (780 nm to 1400 nm) radiance, \(L_{IR}\), as viewed by the eye for exposure times greater than 10 s shall be limited to [EN 62471 4.3.6]:

$$L_{IR} = \sum_{780}^{1400} L_{\lambda} \times R(\lambda) \times \Delta \lambda \leq \frac{6000}{\alpha} \quad \left[\frac{\text{W}}{\text{m}^2 \cdot \text{sr}}\right] \quad \text{for } (t > 10 \text{ s})$$

Where:

• \(L\) is the spectral radiance,
• \(R(\lambda)\) is the burn hazard weighting function,
• \(\Delta \lambda\) is the bandwidth in nm,
• \(t\) is the exposure time in seconds,
• \(\alpha\) is the angular subtense in radians.

Thermal hazard exposure limit for the skin

In addition to ocular safety, EN 62471 also addresses the risk of thermal injury to the skin caused by prolonged exposure to infrared radiation. Since the skin can absorb IR radiation over a broad area, excessive exposure may lead to surface heating, burns, or long-term tissue damage. However, for exposure durations exceeding 10 seconds over larger areas, the standard notes that pain is typically perceived before any actual tissue damage occurs. As a result, an individual's natural aversion response due to discomfort generally limits exposure well before injury is possible. For this reason, thermal hazard exposure limits for the skin are not further considered.

[...] exposure limit is based on skin injury due to a rise in tissue temperature and applies only to small area irradiation. Exposure limits for periods greater than 10 s are not provided. Severe pain occurs below the skin temperature required for skin injury, and an individual's exposure normally will be limited for comfort. Large area irradiation and heat stress are not evaluated since this involves consideration of heat exchange between the individual and the environment, physical activity, and various other factors, which cannot be applied in a product safety standard, but must be evaluated by environmental heat-stress criteria. [EN 62471 4.3.8 (Note)]

ICNIRP

ICNIRP, the International Commission on Non-Ionizing Radiation Protection, is an independent organization that provides scientific guidance on the health effects of non-ionizing radiation, including infrared. In its 2006 and 2013 publications, ICNIRP addresses exposure limits and potential health impacts. The 2006 paper, ICNIRP Guidelines on Limits of Exposure to Broad-Band Incoherent Optical Radiation (2006), includes the relevant skin exposure limit in formula 4b on page 639 (or page 11 of the document). The 2013 paper, ICNIRP Guidelines on Limits of Exposure to Incoherent Visible and Infrared Radiation (2013), presents an updated limit in formula 21 on page 88 (or page 18 of the document).

What "Exempt Group" means

IEC 62471 (EN 62471) defines four photobiological risk groups ordered from lowest to highest risk: Exempt, Risk Group 1 (Low Risk), Risk Group 2 (Moderate Risk), and Risk Group 3 (High Risk). A source classified as Exempt Group under IEC 62471 is placed in the lowest risk category defined by the standard. This classification does not constitute a guarantee of safety under all possible real-world use conditions. For this reason, always follow the safety notes in the Overview tab.

The FFVR-INDEX-V2 was classified in the Exempt Group for every hazard category evaluated, for both illuminated modules tested.

What was tested

• Device: Eye & Face Tracking Kit for Valve Index, model FFVR-INDEX-V2
• Components evaluated: the eye module and the face module. Both eye modules (left and right) are identical in construction and driven by the same circuit; the report evaluates the eye-module design.
• Emission mode: continuous (not pulsed)

How it was tested

• Standard: EN 62471:2008, Photobiological Safety of Lamps and Lamp Systems
• Laboratory: Shenzhen Southern LCS Compliance Testing Co., Ltd.
• Test date: April 16, 2026 (report issued April 17, 2026)
• Operating conditions: DC 5 V supply, ambient 25 ± 1 °C, stable
• Measurement system: EVERFINE OST-300 optical radiation safety test system
• Report number: LCSB03236073S

Measured emissions vs. EN 62471 exposure limits

The tables below list the values recorded in the test report alongside the applicable Exempt Group limits. Measured values are within the applicable limits under the test conditions described in the referenced report. Where used, α denotes the angular subtense of the source in radians as defined per hazard category in EN 62471.

Eye module

Face module

Download the test report (PDF, 18 pages) →

To constrain infrared emissions, the LED current is limited by three independent mechanisms spanning both hardware and software, designed so that current limiting does not rely solely on software.

Additionally, a substantial increase in IR output would normally become visible in practice: overexposure in the eye-tracking application results in a washed-out or unusable image, indicating that something is wrong.

Eye Safety Measures

The hardware includes three independent safety mechanisms that limit the current and therefore the LED output power:

Software-Based Current Limiting
The LED current is adjustable via software, allowing precise control over the brightness. A maximum limit is enforced in the firmware, keeping the LEDs within the intended operating range under normal conditions.

Hardware Limiting via the AW9967DNR LED Driver
The LED driver (AW9967DNR) has a built-in current limiter that sets a hard cap per output channel. This hardware safeguard is designed to keep the current below predefined values even if the software fails or misbehaves.

Polyfuse Protection (10 mA per eye module)
Each eye module is protected by its own polyfuse rated to trip at around 10 mA. If, for any reason, the hardware current limit fails, the polyfuse limits the current by significantly increasing its resistance. Once normal conditions are restored, the fuse resets automatically.