5. Summary and conclusions
5.1. The evidence found for this review was very limited. There was no evidence which
demonstrated any health impact of LED street lighting directly (beyond alternative
sources of lighting).
5.2. There is some evidence to suggest that exposure to artificial light at night can have
some negative impact on the body’s natural circadian phasing due to the interference
with melatonin production. There is some emerging evidence that this effect can lead to
negative health impacts including certain cancers, and obesity. This effect of disrupting
melatonin production may be greater when the light in that exposure is shorter
wavelength (i.e bluer). There is more blue light emitted by LEDs of a higher colour
temperature (4,000k). These factors suggest a plausible risk to health from street
lighting, that may be increased by using LED street lighting with a colour temperature of
around 4,000k. However, the quantity and quality of the evidence available at this time
is deemed insufficient to warrant a recommendation that this level of lighting should not
be used, nor is there sufficient evidence to suggest a ‘safe’ colour temperature
threshold.
5.3. Whilst it would be precautionary to suggest installing LED street lighting at a lower
colour temperature (i.e.2,700-3,000K), it is clear that this would be financially unviable
for Stockport Council. If this scheme were not to be implemented, cost savings to the
equivalent value would need to be delivered from alternative schemes. It is considered
likely that any other such schemes may have health impacts of a similar or greater
likelihood and/or magnitude, but that would need to be reviewed by a health impact
assessment of any alternative proposals.
5.4. To minimise any potential increased risk as described above, it is recommended that the
street lighting team considers the following as part of the testing and implementation of
LED street lighting within Stockport. These are suggested as precautionary response to
a plausible but not proven effect on health due to increased dispersion of blue light from
LED street lighting with a colour temperature of 4,000K:
The lighting should be directed downwards, dispersed as little as possible from
the vertical
The lighting units in residential areas are installed with shielding surrounding
them to minimise direct and dispersed light entering residents’ homes
(particularly bedrooms).
It would be advisable to design the LED luminaire so that hotspots are not
visible within the road user’s normal field of view. Low-cost plastic beamshaping optics could be used to diffuse the source and to tailor the footprint of
the light pattern at ground level. Alternatively, the LEDs could be recesse