The problems of LED lighting can be resumed in three main areas: the protection of the night sky and the luminous glare, human health, especially in terms of night time illumination and interaction with the circadian cycle and, finally, the effects of lighting in night time ecosystems.

LIGHT POLLUTION

Well-used LED lighting can contribute to diminishing night time luminous glare, however the use of a much more efficient technology can in itself lead to increased light levels which would lead to a greater luminous glare. It is recommended that the diffusion of LED technology is accompanied by actions for to promote a new culture of light, which avoids the tendencies of excess that are so entrenched in our society, so that resource savings can be effectively achieved thanks to LED lighting, whilst limiting light pollution. The LEDs can be a great ally in this if they are combined with suitable control systems for the regulation of the luminous flux and suitable optical systems for each application.

For some time, an interdisciplinary consensus has been emerging which can usually be summarised in a series of points that already form part of good practice in lighting engineering:

1. Use lighting where it is really necessary
2. Use lighting during time periods when it is really necessary
3. Avoid the emission of luminous flux above the horizontal.
4. Avoid light intrusion (emission of luminous flux to areas other than that which needs to be illuminated)
5. Use lighting levels adjusted to requirements of use, with possible temporary intensity regulation
6. Use lighting with spectral characteristics suitable for the intended use, limiting the short wavelength light (blue) as much as possible.

Regulationand directionality:

This group recommends that the technical means necessary to take advantage of the possibilities light pollution reduction be introduced into the projects, whenever possible, thanks to the controllable and directionable characteristics of the LEDs.

Energy efficiency and light pollution:

It is recommended that the diffusion of LED technology is accompanied by actions for to promote a new culture of light, which avoids the tendencies of excess that are so entrenched in our society, so that resource savings can be effectively achieved thanks to LED lighting, whilst limiting light pollution.

Spectral considerations: blue light and light pollution:

It should be recommended that, in lighting reforms that imply movement to a whiter or bluish light than the existing one, it is systematically used at sufficiently reduced levels (always maintaining what is required by the regulations, safety and usage requirements of the illuminated spaces). 

POSSIBLE HEALTH RISKS OF LED LIGHTING

1. The circadian system must function properly to maintain good health. Light is the main synchroniser of the circadian system and so it is important that day is day and night is night, which implies making proper use of lighting both inside and outside of buildings, and respecting a minimum number of hours of darkness.

2. In general terms, normal indoor lighting levels during daylight hours, whilst sufficient to ensure visual performance, are markedly lower than those found in the natural environment. On the contrary, at night, both indoors and outdoors, artificial lighting levels are significantly higher than the natural lighting levels to which we are biologically accustomed. Healthy lighting should seek to recover the day-night contrast, increasing the former and decreasing the latter.

3. Light received after daylight hours in significant quantities or with inadequate spectral composition can disrupt the circadian regulation system, with potential negative effects on human health.

4. The effects of light on human physiology depend on a large number of factors, including intensity, spectrum, duration of exposure, time at which exposure occurs, the way in which light is administered, history of previous light exposure and the age of the person. Irrespective of other variables, blue light has much more potential than other wavelengths to cause significant effects on the circadian system. These effects can be caused by light of any spectral composition, however, if it is of sufficient intensity.

5. As for outdoor night lighting, not only the energy efficiency criteria should prevail, so lighting with a reduced blue band spectrum, reducing the colour temperature (CCT) should be recommended for public lighting.
   Unnecessarily high lighting levels should also be lowered.

6. When remodelling old outdoor lighting installations or installing new models, taking into account the fact that, at equal luminance levels, the intensity of the negative effects on people and the environment display an positive correlation with the colour temperature, tending to increase significantly when this is increased (although with significant variations depending on the technology), it should be ensured that the new lighting does not create negative effects on the circadian system, by using light sources with low blue light content or variable systems that allow a decrease of both the colour temperature and the level of illumination throughout the evening, reaching the lowest possible levels late at night.
7. Manufacturers must provide the emission spectrum of their lighting and luminaires in the same way that their luminous efficacy or energy efficiency is reported.

8. It is recommended that the relationship between the illuminance and the colour temperature of the sources in outdoor lighting installations is maintained within levels compatible with the Kruithof curves.

9. On the other hand, it is essential to develop regulations to prevent the intrusion of public lighting intrusion into the private domain that takes into account the effects on human health described in this document. The maximum intrusive light levels established in ITC-EA-03 of Royal Decree 1890/2008, of November 14, which approves the Regulation of energy efficiency in outdoor lighting installations, and its complementary technical instructions EA-01 to EA-07, are expressed in photometric quantities, which are useful for characterising the visual effects of light, and should be scrupulously respected, but are not directly applicable to the prevention of unwanted effects on human health, which depend on spectral sensitivity functions different to photopic or scotopic vision.

10. Recommendations for street lighting are also applicable for indoor lighting. It is necessary to develop technology that minimises circadian disruption at home and at work, while maintaining the required visual performance. In particular, in view of the fact that excessive light exposure at night, including that which is due to the use of luminescent screens, can cause sleep disruption and aggravate disorders, especially in minors, it is recommended to use light sources with the minimum possible blue light content during night hours.

11. During the daylight hours, in cases where natural light cannot be used, it is recommended to raise the lighting levels and the colour temperature of the lamps, especially in the morning, maintaining the luminance of the same within safe limits.

12. To protect the eyesight against the risks specifically contemplated in EN 62471, legal limits must be established on the risk group of lamps that can be installed indoors and outdoors for general purpose lighting.

13. For protection against photooxidative risks not covered in EN 62471 (among others, acute exposure in periods of time greater than 10,000s and chronic exposure to levels below the maximum levels set in the standard), use sources of light with the lowest possible content within the blue light damage sensitivity band.
14. In accordance with the ANSES recommendations, both manufacturers, as well as authorities and independent laboratories should quantitatively assess and report on the wear of the phosphor layers of the pc-LED sources, which could, over time, lead to a higher level of the photobiological risk group.

{82 Researchers should unify the way in which light is measured, to facilitate comparisons between studies, or alternatively include both radiometric and photometric measurements.

16. Many published articles identify exposure to night light in humans by satellite images of the reflected brightness, and there is hardly any data on the light that subjects receive at an individual level, so it would be advisable to move forward in the study of exposure to individual levels in order to establish references.

17. Many experimental studies on the effects of light are carried out in nocturnal animals which are extremely sensitive to light and whose melatonin secretion is in phase with their period of activity, rather than in antiphase as is the case with humans. For this reason, it is possible that we are unaware of many of the effects of exposure to night light on diurnal species.

18. The precautionary principle should be applied, and we have an obligation to work on the development of new healthy lighting technologies that safeguard the human body clock and do not interfere with the normal circadian rhythms of animals and plants.