{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,8]],"date-time":"2026-04-08T18:16:04Z","timestamp":1775672164314,"version":"3.50.1"},"reference-count":23,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,6,21]],"date-time":"2021-06-21T00:00:00Z","timestamp":1624233600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Since photoplethysmography (PPG) sensors are usually placed on open skin areas, temperature interference can be an issue. Currently, green light is the most widely used in the reflectance PPG for its relatively low artifact susceptibility. However, it has been known that hemoglobin absorption peaks at the blue part of the spectrum. Despite this fact, blue light has received little attention in the PPG field. Blue wavelengths are commonly used in phototherapy. Combining blue light-based treatments with simultaneous blue PPG acquisition could be potentially used in patients monitoring and studying the biological effects of light. Previous studies examining the PPG in blue light compared to other wavelengths employed photodetectors with inherently lower sensitivity to blue, thereby biasing the results. The present study assessed the accuracy of heartbeat intervals (HBIs) estimation from blue and green PPG signals, acquired under baseline and cold temperature conditions. Our PPG system is based on TCS3472 Color Sensor with equal sensitivity to both parts of the light spectrum to ensure unbiased comparison. The accuracy of the HBIs estimates, calculated with five characteristic points (PPG systolic peak, maximum of the first PPG derivative, maximum of the second PPG derivative, minimum of the second PPG derivative, and intersecting tangents) on both PPG signal types, was evaluated based on the electrocardiographic values. The statistical analyses demonstrated that in all cases, the HBIs estimation accuracy of blue PPG was nearly equivalent to the G PPG irrespective of the characteristic point and measurement condition. Therefore, blue PPG can be used for cardiovascular parameter acquisition. This paper is an extension of work originally presented at the 42nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society.<\/jats:p>","DOI":"10.3390\/s21124241","type":"journal-article","created":{"date-parts":[[2021,6,21]],"date-time":"2021-06-21T13:29:58Z","timestamp":1624282198000},"page":"4241","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Blue as an Underrated Alternative to Green: Photoplethysmographic Heartbeat Intervals Estimation under Two Temperature Conditions"],"prefix":"10.3390","volume":"21","author":[{"given":"Evgeniia","family":"Shchelkanova","sequence":"first","affiliation":[{"name":"Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu, Fukuoka 808-0135, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Liia","family":"Shchapova","sequence":"additional","affiliation":[{"name":"Omsk State Technical University, 11 Prospekt Mira, 644050 Omsk, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexander","family":"Shchelkanov","sequence":"additional","affiliation":[{"name":"Omsk State Technical University, 11 Prospekt Mira, 644050 Omsk, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tomohiro","family":"Shibata","sequence":"additional","affiliation":[{"name":"Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu, Fukuoka 808-0135, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,6,21]]},"reference":[{"key":"ref_1","first-page":"131","article-title":"Optical properties of the human skin","volume":"2","author":"Gajinov","year":"2010","journal-title":"Serb. J. Dermatol. Venereol."},{"key":"ref_2","unstructured":"Lee, J., Matsumura, K., Yamakoshi, K., Rolfe, P., Tanaka, S., and Yamakoshi, T. (2013, January 3\u20137). Comparison between red, green and blue light reflection photoplethysmography for heart rate monitoring during motion. Proceedings of the 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Osaka, Japan."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Matsumura, K., Rolfe, P., Lee, J., and Yamakoshi, T. (2014). iPhone 4s photoplethysmography: Which light color yields the most accurate heart rate and normalized pulse volume using the iPhysioMeter application in the presence of motion artifact. PLoS ONE, 9.","DOI":"10.1371\/journal.pone.0091205"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Maeda, Y., Sekine, M., Tamura, T., Moriya, A., Suzuki, T., and Kameyama, K. (2008;, January 20\u201325). Comparison of reflected green light and infrared photoplethysmography. Proceedings of the 2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vancouver, BC, Canada.","DOI":"10.1109\/IEMBS.2008.4649649"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Shchelkanova, E., Shchelkanov, A., Shchapova, L., and Shibata, T. (2020, January 20\u201324). An Exploration of Blue PPG Signal Using a Novel Color Sensor-based PPG System. Proceedings of the 2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Montreal, QC, Canada.","DOI":"10.1109\/EMBC44109.2020.9175745"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"025007","DOI":"10.1088\/1361-6579\/ab009b","article-title":"Optimal fiducial points for pulse rate variability analysis from forehead and finger photoplethysmographic signals","volume":"40","author":"Peralta","year":"2019","journal-title":"Physiol. Meas."},{"key":"ref_7","first-page":"2945","article-title":"Can PPG be used for HRV analysis?","volume":"2016","author":"Pinheiro","year":"2016","journal-title":"Annu. Int. Conf. IEEE Eng. Med. Biol. Soc."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1155\/2015\/516826","article-title":"Extraction of heart rate variability from smartphone photoplethysmograms","volume":"2015","author":"Peng","year":"2015","journal-title":"Comput. Math. Methods Med."},{"key":"ref_9","first-page":"1","article-title":"A photoplethysmography smartphone-based method for heart rate variability assessment: Device model and breathing influences","volume":"57","year":"2019","journal-title":"Biomed. Signal Process. Control"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Ferrer-Mileo, V., Guede-Fernandez, F., Fern\u00e1ndez-Chimeno, M., Ramos-Castro, J., and Garc\u00eda-Gonz\u00e1lez, M.A. (2015, January 25\u201329). Accuracy of heart rate variability estimation by photoplethysmography using a smartphone: Processing optimization and fiducial point selection. Proceedings of the 2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Milan, Italy.","DOI":"10.1109\/EMBC.2015.7319686"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"272","DOI":"10.1055\/s-2008-1040549","article-title":"Phototherapy and the photobiology of bilirubin","volume":"8","author":"McDonagh","year":"1988","journal-title":"Semin. Liver Dis."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"170","DOI":"10.3109\/14764172.2015.1007064","article-title":"A randomized controlled study for the treatment of acne vulgaris using high-intensity 414 nm solid state diode arrays","volume":"17","author":"Ash","year":"2015","journal-title":"J. Cosmet. Laser Ther."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1001\/archderm.140.1.41","article-title":"Photodynamic therapy with aminolevulinic acid topical solution and visible blue light in the treatment of multiple actinic keratoses of the face and scalp: Investigator-blinded phase 3 multicenter trials","volume":"140","author":"Piacquadio","year":"2004","journal-title":"Arch. Dermatol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"215","DOI":"10.1016\/j.measurement.2019.06.023","article-title":"Novel high-resolution nanosensor-based measuring equipment for ECG recording","volume":"146","author":"Avdeeva","year":"2019","journal-title":"Meas. J. Int. Meas. Confed."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"135","DOI":"10.1177\/096228029900800204","article-title":"Measuring agreement in method comparison studies","volume":"8","author":"Bland","year":"1999","journal-title":"Stat. Methods Med. Res."},{"key":"ref_16","first-page":"709","article-title":"A new biometrical procedure for testing the equality of measurements from two different analytical methods. Application of linear regression procedures for method comparison studies in Clinical Chemistry, Part. I","volume":"21","author":"Passing","year":"1983","journal-title":"J. Clin. Chem Clin. Biochem"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"709","DOI":"10.1080\/03091902.2018.1513578","article-title":"Quantification of error between the heartbeat intervals measured from photoplethysmogram and electrocardiogram by synchronization","volume":"42","author":"Kuntamalla","year":"2018","journal-title":"J. Med. Eng. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1080\/02640414.2020.1767348","article-title":"Validity of Wrist-Worn photoplethysmography devices to measure heart rate: A systematic review and meta-analysis","volume":"38","author":"Zhang","year":"2020","journal-title":"J. Sports Sci."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Phillips, J.P., and Kyriacou, P.A. (2014, January 26\u201330). Comparison of methods for determining pulse arrival time from Doppler and photoplethysmography signals. Proceedings of the 2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Chicago, IL, USA.","DOI":"10.1109\/EMBC.2014.6944453"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"180076","DOI":"10.1038\/sdata.2018.76","article-title":"An optimal filter for short photoplethysmogram signals","volume":"5","author":"Liang","year":"2018","journal-title":"Sci. Data"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1117\/1.JBO.23.12.120901","article-title":"Review of light parameters and photobiomodulation efficacy: Dive into complexity","volume":"23","author":"Zein","year":"2018","journal-title":"J. Biomed. Opt."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/JTEHM.2014.2360200","article-title":"The effect of light conditions on photoplethysmographic image acquisition using a commercial camera","volume":"2","author":"Liu","year":"2014","journal-title":"J. Transl. Eng. Health Med."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Akay, M. (2006). Wiley Encyclopedia of Biomedical Engineering, Wiley-Interscience.","DOI":"10.1002\/9780471740360"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/12\/4241\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:20:16Z","timestamp":1760163616000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/12\/4241"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,6,21]]},"references-count":23,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2021,6]]}},"alternative-id":["s21124241"],"URL":"https:\/\/doi.org\/10.3390\/s21124241","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,6,21]]}}}