Discussion
Biological organisms have evolved over millions of years to adapt to the day/night cycle, with approximately half of the 24 hour period being filled with light from the sun, and the other half filled with darkness and small amounts of light from the moon and stars. The circadian rhythms of these organisms are controlled by light, the wavelengths of the light, and the absence of light. The introduction of Artificial Light At Night (ALAN) is negatively impacting the functioning of these organisms.
Organisms from insects to fish to humans are sensitive to even low levels of artificial light at night. This means that great care must be taken before justifying the addition of any artificial light into the environment, especially at night.
Figure 1 shows that the sun has already set and therefore the DNA of the biological organisms should be informing the organism to go to sleep or to wake up. The darkness will allow some creatures to be protected, while others will use the very low levels of light to navigate. Humans will be using the darkness for sleep and cell repair.
However, the photo also shows that bright, artificial lights have been turned on. The intensity of these lights is not compatible with the darkness requirements of nighttime for biological systems. These lights are interrupting circadian rhythms, disrupting navigation of birds, and attracting insects to their deaths. Light reflected off the clouds results in skyglow and an interruption of critical sleep in humans.
Figure 1 – Bright parking lot lights
Figure 2 shows bright lights at the entrance to motel. Over lighting is common in the motel and hotel industry. Hotel owners will assert that their customers want safety and feel safer under the bright lights. However, there is no evidence that safety is enhanced, but significant evidence that bright lights interrupt sleep which can lead to increases in diseases such as cancer and diabetes.
Figure 2 – Bright lights at motel
Figure 3 shows a parking lot light at full brightness, half brightness and with an 80% reduction in brightness. While the energy use was reduced by approximately 80%, the loss of functionality is barely noticeable or even improved due to reduced glare.
Figure 3 – Reducing brightness reduces energy use.
With regulations limiting the brightness of light, we can reduce energy usage by as much as 80%. For example, San Diego Gas and Electric powers over 145,000 streetlights. While the long-term goal is to eliminate these streetlights completely, let us consider how much energy we can save by simply reducing the brightness. Supposing an average of 10,000 lumens per streetlight at an energy efficiency of 80 lumens per watt, this converts to 125 watts per streetlight. For SDGE, this is 18.125 million watts of electricity being used to light up the night. By reducing the brightness from 10,000 lumens to 2,000 lumens, we reduce the energy used to 25 watts per streetlight and 3.625 million watts of electricity. By reducing brightness, we can simultaneously reduce energy use and increase healthy darkness.
Figure 4 shows common outdoor light levels in the natural world. Our task for nighttime lighting is to illuminate just enough to be able to navigate. We must remain cognizant that each extra lumen of light added into the nighttime environment decreases darkness and increases harm to human health and the environmental system.
Figure 4 – Common Outdoor Light Levels
The chart shows that twilight as approximately 10 lux. Twilight is when the sun is below the horizon and most of the light is the long red wavelengths. This is the time where we begin to use more of our rod cells for vision because these cells are more sensitive to low light conditions. Because darkness is so important to our production of the melatonin hormone, we should refrain from over lighting.
Full moonlight is only 0.1 lux. Since the biological systems on earth have evolved over millions of years to adapt to this 0.1 lux or less during nighttime, we must take care not to disturb this system. This is good news for our energy conservation goals because increasing darkness should automatically result in less energy use.
Figure 5 shows an over lit building that is too bright, wasting energy, causing light pollution, and causing harm to humans and the environment.
Figure 5 – Over Lit building
Figure 6, on the other hand, shows a well shielded, low color temperature light that is just bright enough to allow a person to navigate. The reader may wonder about the unlit areas just outside of the doorway. Human eyes are extremely sensitive and even this tiny amount of light will allow a person to see well beyond just the lit entrance.
Figure 6 – Low Intensity lighting
The photos below show unacceptable and acceptable levels of brightness for nighttime lighting.
Unacceptable
Acceptable
“The interaction between the intensity and spectral composition of artificial light and the adaptation of an organism’s eyes will affect whether visual perception is enhanced, disrupted or unaffected by light pollution, and hence the potential downstream behavioural and ecological effects.” – Cambridge University (2013) – The ecological impacts of nighttime light pollution: a mechanistic appraisal
Proposed Regulations
We propose that all outdoor lighting use the lowest level of brightness to achieve functionality. No light shall exceed 10 lux on the ground or 2,000 lumens at the source. In addition, all outdoor lights must be adequately shielded and diffused, which will help reduce brightness.
The reporting and enforcement mechanism for violations would be the same as for color temperature.