Evaluation of Potential Optical Radiation Hazards from LED Flashlights

ICNIRP Statement on Short Wavelength Light Exposure from Indoor Artificial Sources and Human Health

ABSTRACT

Concerns have been raised about the possibility of effects from exposure to short wavelength light (SWL), defined here as 380-550 nm, on human health. The spectral sensitivity of the human circadian timing system peaks at around 480 nm, much shorter than the peak sensitivity of daytime vision (i.e., 555 nm). Some experimental studies have demonstrated effects on the circadian timing system and on sleep from SWL exposure, especially when SWL exposure occurs in the evening or at night. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has identified a lack of consensus among public health officials regarding whether SWL from artificial sources disrupts circadian rhythm, and if so, whether SWL-disrupted circadian rhythm is associated with adverse health outcomes. Systematic reviews of studies designed to examine the effects of SWL on sleep and human health have shown conflicting results. There are many variables that can affect the outcome of these experimental studies. One of the main problems in earlier studies was the use of photometric quantities as a surrogate for SWL exposure. Additionally, the measurement of ambient light may not be an accurate measure of the amount of light impinging on the intrinsically photosensitive retinal ganglion cells, which are now known to play a major role in the human circadian timing system. Furthermore, epidemiological studies of long-term effects of chronic SWL exposure per se on human health are lacking. ICNIRP recommends that an analysis of data gaps be performed to delineate the types of studies needed, the parameters that should be addressed, and the methodology that should be applied in future studies so that a decision about the need for exposure guidelines can be made. In the meantime, ICNIRP supports some recommendations for how the quality of future studies might be improved.

The potential 'Blue Light Hazard' from LED Headlamps

Many dental personnel use light-emitting diode (LED) headlamps for hours every day. The potential retinal 'blue light hazard' from these white light headlamps is unknown.

METHODS

The spectral radiant powers received from direct and indirect viewing of an electronic tablet, an LED curing light, a halogen headlamp, and 6 brands of LED headlamps were measured using integrating spheres attached to fiberoptic spectroradiometers. The spectral radiant powers were measured both directly and indirectly at a 35 cm distance, and the maximum daily exposure times (t_MAX) were calculated.

RESULTS

The headlamps emitted very different radiant powers, emission spectra, and color temperatures (K). The total powers emitted at zero distance ranged from 47 mW from the halogen headlamp to 378 mW from the most powerful LED headlamp. The color temperatures from the headlamps ranged from 3098 K to 7253 K. The t_MAX exposure times in an 8-hour day when the headlamps were viewed directly at a distance of 35 cm were: 810 s from the halogen headlamp, 53 to 220 s from the LED headlamps, and 62 s from the LED curing light. Light from the LED headlamps that was reflected back from a white reference tile 35 cm away did not exceed the maximum permissible exposure time for healthy adults. Using a blue dental dam increased the amount of reflected blue light, but t_MAX was still greater than 24 hours.

CONCLUSIONS

White light LED headlamps emit very different spectra, and they all increase the retinal 'blue light hazard' compared to a halogen source. When the headlamps were viewed directly at a distance of 35 cm, the 'blue light hazard' from some headlamps was greater than from an LED curing light. Depending on the headlamp brand, t_MAX could be reached after only 53s. The light from the LED headlamps that was reflected back from a white surface that was 35 cm away did not exceed the maximum permissible ocular exposure limits for healthy adults.

CLINICAL RELEVANCE

Reflected white light from dental headlamps does not pose a blue light hazard for healthy adults. Direct viewing may be hazardous, but the hazard can be prevented by using the appropriate blue-light-blocking glasses.

Retinal Protection from LED-Backlit Screen Lights by Short Wavelength Absorption Filters

(1) Background: Ocular exposure to intense light or long-time exposure to low-intensity short-wavelength lights may cause eye injury. Excessive levels of blue light induce photochemical damage to the retinal pigment and degeneration of photoreceptors of the outer segments. Currently, people spend a lot of time watching LED screens that emit high proportions of blue light. This study aims to assess the effects of light emitted by LED tablet screens on pigmented rat retinas with and without optical filters. (2) Methods: Commercially available tablets were used for exposure experiments on three groups of rats. One was exposed to tablet screens, the other was exposed to the tablet screens with a selective filter and the other was a control group. Structure, gene expression (including life/death, extracellular matrix degradation, growth factors, and oxidative stress related genes), and immunohistochemistry in the retina were compared among groups. (3) Results: There was a reduction of the thickness of the external nuclear layer and changes in the genes involved in cell survival and death, extracellular matrix turnover, growth factors, inflammation, and oxidative stress, leading decrease in cell density and retinal damage in the first group. Modulation of gene changes was observed when the LED light of screens was modified with an optical filter. (4) Conclusions: The use of short-wavelength selective filters on the screens contribute to reduce LED light-induced damage in the rat retina.