Light at Night Index (LANI) Description and Links

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Background

Artificial lighting at night has increased dramatically over the last 70 years throughout the world. One of the most obvious effects has been the obscuring of the view of the natural sky and has therefore long been a concern of astronomers. More recently, evidence indicating adverse health effects due to artificial light at night (ALAN) has been presented. In particular, a role for ALAN as a risk factor for breast cancer, heart disease, and obesity. In addition, ALAN is recognized to have some significant impacts on the environment with numerous examples of disruption of longstanding animal behaviors and ecosystem equilibriums.

Given that ALAN is fact of modern life it may be useful to consider not just the absolute brightness in a specific location, but rather consider the range of ALAN use on a more global scale to determine “best practice” levels. This would allow for the identification of attainable levels, the recognition of areas where improvements could be expected and areas of unusual concern. This paper describes the development of an indexing tool, Light at Night Index (LANI), to help in this type of analytical approach.

Data sources

The scope of our approach is to consider communities in the United States with a population greater than 500 people.  Data encompassing all of these communities is therefore required. This need is fulfilled using data from the U.S Census bureau.  Light at night data spanning the country is collected by satellite imaging and that data is available for moonless, cloud free nights through the Earth Observation Group, NOAA National Geophysical Data Center. Median radiance values for locations were obtained using moonless, cloud free nights for January, February, and March 2015.

Observatory positions were taken from Google maps and from a compilation of sites maintained by the Minor Planet Center.

Methods for collecting and assembling data

Preliminary data preparation.

The U.S. census bureau Places ESRI file (US_2010Places_DP1.shp) was initially trimmed to remove communities from Alaska due to problems with obtaining radiance values at high latitudes and the atypical community configurations (e.g. small populations with very large undeveloped community boundaries). Puerto Rico was also trimmed from the data file. Communities with populations of less than 500 were then removed from consideration.

Calculation of the LANI:

The proposed LANI is to reflect community efficiency in night lighting and to allow the comparison of use between communities. This will allow for the establishment of target levels of night lighting based on the range of observed utilization. The use of lighting is measured as observed radiance per person in the community. The impact of community development and density is measured as radiance per housing unit and radiance per community extent (area). The three measures of community night lighting are standardized and combined into the final index.

Standardization.

The first step in calculating the LANI is the standardization of the indicator data. The purpose of this step is to adjust for the varying metrics and scales of indicators. The indicator score for each unit is standardized as its difference from the unit with a minimum value divided by the difference between a maximum and minimum. The maximum and minimum are chosen to encompass the true maximum and minimum of the indicator score series. This is to allow for use of a consistent standard between, for example, different years of data collection even if there is a trend to increase or decrease in magnitude. In addition, the minimum is chosen to avoid a 0 value.

If the indicator data is an array I[n][m] with n number of indicators and m the number of geographic areas, the standardized score is:

The summary index (LANI) is calculated for each, m, geographic feature by calculation of the geometrical mean of the standardized index (Is[n][m]) for each indicator according to:

The LANI is then transformed to a scale of 1 to 100 for ease of manipulation and inverted so that a larger LANI score is indicative of a better (i.e. more efficient) use of light energy and a smaller value represents a more wasteful situation. This transformation is:

Properties of the LANI

The distribution of LANI scores among the 19,350 qualifying communities is not normal (Shapiro-Wilk statistic = 0.697), but instead skewed toward the left (i.e. toward lower scores indicating decreased efficiency of night time lighting). This is more obvious in the normality plot which shows a departure from the expected values at a z-score of about -1.5, suggesting that at least 1300 communities are less efficient than expected.

 

Figure 1. Frequency distribution of the LANI values.

 

Highest and lowest ranked communities.

 

Table 1. Listing of the top 10 and bottom 10 percentile ranked communities out of 19,350. The actual LANI score, the total integrated community radiance and community population size
Top 10 Communities					Bottom 10 Communities
Community	LANI	R†	Size		Community	LANI	R	Size
Paauilo, HI	99.93	7	595		Bedford Park Village, IL	5.18	39,281	580
Hawaiian Ocen View, HI	99.91	128	4,437		Cuyahoga Heights, OH	10.71	19,439	638
Ainaloa, HI	99.89	40	2,965		Medley Town, FL	20.85	22,592	838
Hawaiian Paradise Park, HI	99.89	193	11,404		Forest View Village, IL	28.25	8,482	698
Nanawale Estates, HI	99.88	28	1,426		University at Buffalo, NY	37.57	14764	6,066
Fern Acres, HI	99.86	51	1,504		Burns Harbor Town, IN	43.16	19,408	1156
Mesa del Caballo, AZ	99.85	13	765		Hodgkins Village, IL	45.25	15,747	1897
Orchidlands Estates, HI	99.84	96	2,815		Roxana Village, IL	48.52	20,692	1542
Leilani Estates, HI	99.83	55	1,560		Irwindale City, CA	49.90	16,405	1422
Papaikou, HI	99.83	32	1,314		Highland Hills, OH	52.68	7,715	1130
†R, total radiance (Wsr-1)

 

 

 

Astronomical observatories and LANI of surrounding communities.

Astronomical optical observatories have a keen interest in the night lighting of surrounding communities and actively seek cooperation from local government in minimizing their lighting levels. The LANI score provides a means to evaluate the relative success of communities in utilizing light efficiently and can provide a meaningful resource for identifying communities that could reasonably improve their light at night status.

 

 

The scores for all of the 468 observatories included in this study can be viewed on our map of observing sites in the United States.