Table 1 below lists various sources used in street and area lighting (among other applications) along with selected characteristics related to their spectral content, normalized for equivalent lumen output. The table was updated in June 2017 from an earlier version to increase the number of LED samples on which the corresponding data ranges are based (see Table 2). Data for each source includes a measured correlated color temperature (CCT), the calculated percentage of radiant power contained in "blue wavelengths" (defined here from the literature related to sky glow as wavelengths between 405 and 530 nanometers [nm]), and the corresponding scotopic and melanopic multipliers that are shown relative to a high-pressure sodium (HPS) baseline due to its predominance in the existing outdoor lighting market.
Table 1: Selected blue light characteristics of various outdoor lighting sources at equivalent lumen output.
|Row||Light source||Luminous Flux (lm)||CCT (K)||% Blue*||Relative Scotopic Potential||Relative Melanopic Potential**|
|A||PC White LED||1000||2700||15% - 21%||1.74 - 2.33||1.90 - 2.82|
|B||PC White LED||1000||3000||18% - 25%||1.88 - 2.46||2.09 - 3.06|
|C||PC White LED||1000||3500||22% - 28%||2.04 - 2.54||2.34 - 3.25|
|D||PC White LED||1000||4000||26% - 33%||2.11 - 2.77||2.36 - 3.64|
|E||PC White LED||1000||4500||32% - 35%||2.39 - 2.94||2.83 - 3.95|
|F||PC White LED||1000||5000||35% - 40%||2.61 - 3.43||3.22 - 4.69|
|G||PC White LED||1000||5700||39% - 45%||2.75 - 3.39||3.42 - 4.62|
|H||PC White LED||1000||6500||43% - 48%||3.12 - 3.97||4.10 - 5.87|
|I||Narrowband Amber LED||1000||1606||0%||0.36||0.12|
|J||Low Pressure Sodium||1000||1718||0%||0.34||0.10|
|K||PC Amber LED||1000||1872||1%||0.70||0.42|
|L||High Pressure Sodium||1000||1959||9%||0.89||0.86|
|M||High Pressure Sodium||1000||2041||10%||1.00||1.00|
* Percent blue calculated according to LSPDD: Light Spectral Power Distribution Database, http://galileo.graphycs.cegepsherbrooke.qc.CA/app/en/home.
** Melanopic content calculated according to CIE Irradiance Toolbox, http://files.cie.co.at/784_TN003_Toolbox.xls (download), 2015.
† Moonlight CCT provided by Telelumen, LLC.
The ranges listed for the LED properties reflect the fact that various products often differ from one another in terms of their precise spectral content, even when binned together in the same nominal CCT, and each CCT bin listed in the table contains numerous product samples. The exact number of samples in each bin ranges from 20 (for 5700 K) to 162 (for 3000 K), with others falling in between (457 samples in all; see Table 2). Conventional light sources are all represented by single values though they would likewise be more accurately characterized by a range (albeit much narrower than LED).
Table 2: Number of LED products underlying the data ranges shown for each CCT bin in Table 1.
|Count||Row||Light source||Luminous Flux (lm)||CCT (K)|
|59||A||PC White LED||1000||2700|
|162||B||PC White LED||1000||3000|
|53||C||PC White LED||1000||3500|
|51||D||PC White LED||1000||4000|
|36||E||PC White LED||1000||4500|
|44||F||PC White LED||1000||5000|
|20||G||PC White LED||1000||5700|
|32||H||PC White LED||1000||6500|
Most importantly, performing a calculation with these values only provides an idea of the relative potential to cause health or other impacts, rather than detailing any actual impacts likely to occur. Impacts are critically related to additional factors such as intensity, length of exposure, and other exogenous variables that are not represented in the table.
Nevertheless, the potential influence of blue wavelengths is immediately evident in all "white light" sources containing them. In addition, as demonstrated by the relative properties displayed by conventional lighting sources in the table, the blue light issues that have been raised in recent debate are clearly nothing new to our lighted environment. What is new is our increased understanding of their potential influence regarding human and environmental health issues, as the related research has evolved. Much work remains to put any associated potential risk into a realistic context, however.