Safety concerns - IR power?

[Simon Schulz]

Hi!

I was wondering if you checked/calculated the maximum allowable ir illumination
to the human eye. As there is no adaption of the iris when radiated by IR light
i am wondering if the ir light could hurt your eye.

Regards,
Simon

[Will Patera]

Hi Simon, 

Thanks for addressing this question.  

There is a considerable amount of literature on this topic within the eye tracking research.  Here is a link to a 60 month long study conducted by COGAIN (Communication by Gaze Interaction), titled "Exploration of safety issues in Eyetracking."  An excerpt from this study on page 11:

The eye is well adapted to protect itself against overly intense broad-band optical radiation (ultraviolet, visible and infrared radiant energy) from the natural environment and mankind has learned to use protective measures, such as hats and eye-protectors, to shield against the harmful effects upon the eye from very intense ultraviolet radiation (UVR) and blue light present in sunlight over snow or sand. The eye is also protected against bright light by the natural aversion response to viewing brightly visible light sources. The aversion response normally protects the eye against injury from viewing bright light sources such as the sun, arc lamps and welding arcs, since this aversion limits the duration of exposure to a 

fraction of a second (about 0.25 s). The infrared LEDs employed in most infrared LED eyetrackers do not, however, produce a strong 

aversion response, as they are barely visible, and the spectral emission is limited to the near-infrared (IRA, 780-1400 nm) spectral band 

And on page 17:

The exposures typical of LED eyetrackers are typically below Maximum Permissible Exposure (MPE) limits, and therefore well below actual retinal injury thresholds (Ham & Mueller, 1989; Sliney et al, 2005). The best available data for retinal injury thresholds for large-image exposure at 810 nm comes from work published by Ham and Mueller (1989) 

Pupil is similar to many other head mounted eye tracking devices that use IR for dark pupil illumination methods.  In early development we calculated and found the IR exposure to be within safe ranges of operation, as we are operating with only 2 low power 850nm IR LEDs.  However we have not conducted any official trials with national or international safety boards, so I encourage you to read the literature on IR exposure.       

   

Best, 

Will  

[Moritz Kassner]

Hey,

I have not seen this paper before. Good find. Most eye-tracker use IR-LEDS for illumination. 

From the same paper there is this excerpt:

LEDs are radiance limited and cannot produce exposure levels at the retina  that even approach the levels that are known to cause retinal thermal injury (ICNIRP, 2000; Sliney, 1997) 

Currently, only short-wavelength blue-violet emitters clearly exceed the more restrictive photochemical 

hazard limits at wavelengths shorter than 550 nm. In other words, the infrared LEDs would have to emit 

far more power to pose a serious acute hazard to the retina. This is theoretically impossible for current 

LEDs.

The leds we use emit 10mWSr at 850nm. Datasheet here: http://www.vishay.com/docs/83397/vsmy1850.pdf

I hope this helps,

m

[micb...@googlemail.com]

Hello,

While reading I found this "kind of older" thread. I also wondered if IR LEDs could harm the eye, when I build a DIY tracker based on ITU Gaze Tracker. I did some research. In the end I asked my neighbor (medical), if he knows something about that topic. He gave me a link to the following study (german only):

http://www.baua.de/de/Publikationen/Fachbeitraege/F2115.html

Publisher is the German Federal Agency for Employment Protection.
They researched the impact of LEDs especially for the human eye.
Since I did not have access to measuring equipment I dropped my research at that point. Nevertheless this could be important for deploying pupil.

Kind regards,
Michael Barz

[Rafael Picanço]

"Eye Safety Related to Near Infrared Radiation Exposure to Biometric Devices"

Nikolaos Kourkoumelis and Margaret Tzaphlidou

DOI 10.1100/tsw.2011.52

2012

Excerpt from this paper:

"The International Commission of Non-Ionizing Radiation Protection (ICNIRP) takes for granted that

infrared radiation poses a risk to the human eye under certain conditions[41]. The norm regarding thermal

lesions for cornea and lens states that the ocular exposure should not exceed 10 mWcm-2 for lengthy

exposures (>1000 sec) and 1.8 t-3/4 Wcm-2 for shorter exposure durations. Retinal exposure limit values

(ELV) for IR-A irradiation and time beyond 10 sec stem from the following formula [...]" (p. 524)

So, an IR-A LED could damage the human eye under certain conditions.

From another (non-medical) paper:

"Building a lightweight eyetracking headgear"

Jason S.Babcock & Jeff B. Pelz

2004

"A critical design parameter of any video-based eyetracker is the

level of infrared power incident on the eye. The retina is

insensitive to energy in the near-infrared, so one cannot rely on

subjective reports of brightness. The irradiance (mW/cm2) at the

eye is a function of the power emitted by the IRED, the area over

which that energy is spread, and the uniformity of the illumination

pattern. An irradiance level less than 10 mW/cm2 is considered

safe for chronic IR exposure in the 720-1400 nm range (Sliney &

Myron, 1980, ICNIRP, 1997, 2000). The IR illuminator in our

system provides adequate illumination for the eye camera with an

irradiance of only 0.8 mW/cm2, well below the recommended

safety level." (p. 2)

They use only one LED, it is important to note.

[Rafael Picanço]

For the ones who care about details, this guide may be useful:

Converting Radiant Intensity in Units of mW/cm2 to mW/sr.
http://optekinc.com/pdf/app%20bulletin%20222.pdf

[Rafael Picanço]

Hi, what is the state of the "official trials with national or international safety boards" of Pupil?

Best,
Rafael

[Pupil Labs Info]

Hi Rafael, 

Pupil is currently in the process of being tested for CE certification.

Best regards, 

Will 

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[je...@cornell.edu]

Can anyone comment on the long-term eye safety of this system in terms of the IR illumination so close to the pupil? I don't really feel like giving myself cataracts.

What is the status of the CE testing? Is CE even the right group to certify this? Seems more like how a laser is categorized, and this isn't a CE thing, more of an ANSI / IEC thing. Is there a maximum permissible exposure? What is it? Are the power levels modulated to safe levels? Has the LED manufacturer published usage guidelines, and are these adhered to?

[Pupil Labs Info]

Hi all,

Pupil hardware is certified for IR safety according to EN 62471:2008. 

For als aspects of the norm including retinal thermal, infrared eye radiation thermal hazard on skin Pupil hardware passes all tests. It is categorised as save for continuos exposure.

I hope this helps!

Best,

Moritz

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[Rafael Picanço]

Hi, I am using pupil for a long time and I am not blind. Moritz is not blind. Will is not blind. No one using pupil ever got anything. If you do not fell safe yet, consider the fact that no single IR led (120 mA + 5-10 spheroradians per square meters) has enough power to couse any harm to your eyes in an iluminated room (lets say, 100 lux to 600 lux), even with chronic exposure and close to your eyes.

[Rafael Picanço]

I need to correct myself : "120 mA + 5-10 spheroradians per square meters" is wrong.

The correct measure is that: "5-10 mW/sr miliwatts per spheroradian" for a single led. Of course, I would appreciate the feedback of some light specialist on this topic. As far as I know, 10 W/sr is safe. Thoses leds are well below this.