In recent years, researchers have pointed to the potential retinotoxicity of blue light emitted by white LEDs at lighting levels classed as “domestic”, which has raised a great deal of concern among consumers and lighting professionals. In 2017, we demonstrated that these conclusions, drawn from experiments carried out on rodents, had to be considered with extreme caution, that there was still no evidence at all that the light produced by white LEDs could be dangerous at domestic light levels, and that it was therefore unjustified to request a revision of the exposure limit values for the general population.. This view is shared by SCHEER [EU Scientific Committee on Health, Environment and Emerging Risks] experts who, in a report issued in July 2018, conclude that there is no evidence of harmful effects of LEDs in normal use, while admitting however that further research is needed to study the effect of blue light on certain more sensitive groups, such as young children where the greater transparency of the crystalline lens at short wavelengths  suggests that LEDs could be more harmful than other types of artificial lamps.
In this context, we took an interest in the issue of very young children (less than one year old), with the aim of understanding the effect of the specific biometry of their eyes and the greater transparency of their crystalline lens on the appropriateness of the current exposure limit values, with regard to the main lamp technologies accessible to the consumer (LED lamps, Tungsten-Halogen lamps, and fluorescent lamps).
Blue light and retinotoxicity: what is the issue?
In the second half of the last century, researchers highlighted the possibility of photochemical damage appearing in rhesus monkeys under the action of high intensity blue light for a relatively short period (from a few seconds to a few hours), characterised by the destruction of photoreceptors and retinal pigmented epithelium (RPE). This type of injury is athermal and is characterised by oxidative stress phenomena: blue light, focused on the retina, which is highly vascularised and oxygenated, expends its energy in the creation of reactive types of oxygen that may lead to lipid peroxidation of retinal cell membranes. These cellular destruction mechanisms are naturally counteracted by the protective action of antioxidants present in the retina and the permanent renewal of the external section of the photoreceptors by phagocytosis in the RPE.
The potential retinotoxicity of blue light is taken into account in the design of lamps and artificial lighting devices and when manufacturers place their products on the European market they are required to ensure their compliance with photobiological safety standards. These standards are centred on an action spectrum  which describes the effectiveness with which short wavelengths can contribute to oxidative stress of the retina. This action spectrum is valid for an adult human. The relationship between retinal illuminance value and light source power is constructed on an eye model using pupil and focal length values which are also typical for the adult eye.
Harmful wavelengths not on the LED spectrum
In humans, eye growth is rapid during the first year of life: pupil diameter and focal length of the eyes of very young children are different from those of an adult. Analysis of the available literature has made it possible to propose an eye model based on typical pupil and focal length values for a very young child’s eye: it can then be demonstrated that retinal illumination considered safe is produced by sources almost three times less powerful than those needed to produce the same illumination on an adult retina.
A third parameter makes a young child’s eye very different from the adult eye: the transparency of the crystalline lens. The crystalline lens is a flexible transparent biconvex lens, located behind the iris, and which allows for focussing. In very young children, the crystalline lens is much more transparent at short wavelengths than in adulthood. To take this phenomenon into account when assessing the photobiological risk associated with a light source, the ICNIRP (International Commission on Non-Ionizing Radiation Protection) recommends applying a specific action spectrum, that of the aphakic eye. So we compared the retinal illumination produced by three spectral power distributions, associated respectively with white phosphor LEDs, Tungsten halogen lamps and fluorescent lamps, taking into account the aphakic action spectrum. It appears that the application of this action spectrum does not increase retinal illumination in blue light produced by the white LED being tested; but the amount of potentially harmful light from the fluorescent lamp or the Tungsten-Halogen lamp is increased by 40% and 35% respectively: the greater transparency of the child’s eye, modelled by the action spectrum of the aphakic eye, favours the transmission of violet wavelengths which are naturally absent from the white LED spectrum, but present in the spectrum of the Tungsten-Halogen and fluorescent lamps.
Demands should be qualified
Due to its specific biometry, the eye of a very young child collects more light than the adult eye; the retinal illumination for a given source, whatever the technology, could be up to 3 times higher than for an adult, which would justify the implementation of specific exposure limit values for certain applications, such as night lights or toys. Our observations also support the need for photobiological safety standards to take into account the greater transparency of the crystalline lens of the eye in very young children, which promotes the transmission of violet light, produced in particular by mercury-based fluorescent lamps or by Tungsten-Halogen lamps but absent from the spectrum of white LEDs.
From a purely spectral point of view, LEDs thus seem less dangerous than older technologies, which makes it possible to qualify certain demands for their prohibition on a precautionary principle basis. In reality, and as is often the case with technological devices, the risk is found at the usage stage. LEDs are found in applications where Tungsten halogen lamps and fluorescent lamps are not used. There are many commercially available toys with powerful white LEDs that can be placed near small children without any limits as to distance or exposure time. Parents should therefore pay particular attention to the light environment of their very young children, by limiting close and prolonged contact with lamps, whatever the technology, while keeping in mind that short wavelength light should not be removed from their light environment since it is a factor in the normal process of eye growth.
 Short wavelength radiation is defined here as visible radiation below 500 nm, including blue and violet light.
 Point S., Blue Light Hazard: are exposure limit values protective enough for newborn infants? Radioprotection (2018). https://doi.org/10.1051/radiopro/2018025
 The action spectrum of blue light describes to what extent different “blue” lengths can cause oxidative stress in the retina.
 Eye without crystalline lens.