Image Projectors and Photobiological Safety Testing

Based on IEC 62471:2006’s approach, a revised retinal thermal hazard weighting function and new emission limits are derived from the ICNIRP 2013 guidelines for incoherent infrared and visible radiation [1], and a measurement distance of one meter from the nearest point of human access is implemented. For image projectors, this plane corresponds to that of the projection lens.

Hazard Hazard Weighting Function Units
UV Skin and Anterior Eye, Es S(λ) W•m-2
UVA Eye, EUVA - W•m-2
Retinal Blue Light, EUVA B(λ) W•m-2•sr-1
Retinal Blue Light Small Source, EB B(λ) W•m-2
Retinal Thermal, LR R(λ) W•m-2•sr-1
IR anterior eye, EIR - W•m-2

*EN/ IEC 62471-5 hazards considered

Image Projectors

According to the source and image technology used, the emission of image projectors may be either pulsed or continuous wave. Pulsed emission is defined as that for which the average radiant power surpasses the peak radiated power at least 1.5 times. In the case of pulsed source, all but the retina thermal hazard are time averaged.

The exit pupil, which is located behind the projection lens, is the apparent source of image projectors. It is essential to determine the angular subtense and location of the exit pupil in the assessment of retinal hazards.

EN/ IEC 62471-5 spectral weighting functions.

Figure 1. EN/ IEC 62471-5 spectral weighting functions.

Projectors have to be set up to least favorable conditions (color, brightness). The throw ratio, which is defined as the distance from between exit pupil to screen to width of image, should be setup based on the projector optics type – interchangeable, zoomable, or fixed lens.

Image projectors are classified according to the degree of risk, from RG0, which causes no reasonably predictable optical hazard to RG3, which is hazardous for brief exposure. RG2 projectors include home-use projectors, while RG0 / RG1 projectors include traditional tungsten halogen slide or film projectors for home use or pico-projectors. RG3 projectors are high power projectors used in theaters or cinemas and are not meant for domestic use.

Image of projector exit pupil.

Figure 2. Image of projector exit pupil.

Labeling requirements are given for RG2 and RG3. Besides labeling, RG2 and RG3 projectors should have a soft start feature to make sure that full emission doesn’t start sooner than one second post initial illumination to facilitate activation of the aversion response. Hazard distance information should be available with RG3 products, to aid in installation restricted control areas and risk evaluation.

References

Bentham Instruments Limited.

This information has been sourced, reviewed and adapted from materials provided by Bentham Instruments Limited.

For more information on this source, please visit Bentham Instruments Limited.

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