Background: Direct laryngoscopy and successful endotracheal intubation require optimal illumination of laryngeal structures. The International Organization of Standardization (ISO) describes minimum adequate laryngoscope illuminance as 500 lux after 10 minutes, and further describes optimal dimensions of the illumination field. Laryngoscope light is subjectively assessed by the anaesthetist as part of theatre preparation. This study sought to describe the illumination of laryngoscopes at two academic hospitals, to compare illumination of incandescent and fibreoptic laryngoscopes and to compare the accuracy of a mobile phone application (app) to a lux meter. Methods: A prospective, contextual, descriptive study was conducted, testing the illumination of 43 laryngoscopes with a lux meter, as well as a mobile phone app. The illumination field size of each laryngoscope was determined. Results: ISO Standard for illumination was met by 8 (18.6%) laryngoscopes, and 11 (25.5%) had an adequate illumination field. Only 4 (9.3%) laryngoscopes met both criteria. The mobile phone app readings were significantly different from those obtained with a lux meter (p = 0.0008). After battery replacement 23 further laryngoscopes demonstrated an adequate illuminance. No significant difference was found between incandescent and fibreoptic laryngoscope illuminance (p = 0.86). Conclusion: This study demonstrated that the available laryngoscopes had poor illuminance. A mobile phone app was not comparable to a lux meter. Routine objective illuminance testing as well as regular battery changes are suggested to be implemented.

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