How hazardous is the sky?

Abstract

The advent of high performance and versatile LED technology is leading to the development of spectrally agile lighting products and systems capable of delivering significant levels of photobiologically active optical radiation. Contemporary lighting systems based on LED and in some cases laser technology can now encompass the ultraviolet, visible and near-infrared regions of the spectrum. This technology has been applied to varied research and development related applications such as photodynamic therapy, dermatology, horticulture and human centric lighting (HCL). Interestingly, human centric lighting includes the possibility to entrain, via blue-green light, the human circadian rhythm and is presently being deployed in trials across selected workplaces and schools in Europe. In another application centred on room lighting, LED lighting technology has been devised which allows ‘artificial skylighting,’ where a room which has no access to natural daylight can be used ‘year-round’ by delivering a timed dose of artificial sunlight considered to be therapeutic and beneficial. In most of these lighting systems, there is a general desire to mimic as closely as possible, an exposure akin to that of natural daylight, and in many regards, the daylight spectrum represents the ‘gold-standard’ which the artificial source should emulate.This paper places the recent development of tuneable spectrum LED technology in context with photobiological safety standards such as IEC 62471 [1], and especially within the context of the blue light photochemical retinal hazard. The exposure limits in the standard are reviewed and compared to metrologically derived radiance values for clear sky, so that the blue light hazard related exposure for artificial daylight sources can be compared with comparable daylight exposures that occur in nature; the purpose being to place artificial daylight exposures in an appropriate context.The paper will describe a software-based methodology where extant, published photometric and radiometric data for natural daylight can be ‘reverse engineered’ to provide insight into any equivalent collateral photobiological hazard in order to compare the exposure (and thereby Exposure Hazard Value) with those present form artificial daylight sources such as an LED skylight; the analysis can be extended to additional non-hazard based action spectra such as ’melanopic’ lighting as may also be required.The intention of the paper is to raise awareness of the direction of development of next-generation lighting technology, with the aim of supporting the establishment of further lighting applications-based standards wherein appropriate exposure limit values for the product may be more clearly defined.The advent of high performance and versatile LED technology is leading to the development of spectrally agile lighting products and systems capable of delivering significant levels of photobiologically active optical radiation. Contemporary lighting systems based on LED and in some cases laser technology can now encompass the ultraviolet, visible and near-infrared regions of the spectrum. This technology has been applied to varied research and development related applications such as photodynamic therapy, dermatology, horticulture and human centric lighting (HCL). Interestingly, human centric lighting includes the possibility to entrain, via blue-green light, the human circadian rhythm and is presently being deployed in trials across selected workplaces and schools in Europe. In another application centred on room lighting, LED lighting technology has been devised which allows ‘artificial skylighting,’ where a room which has no access to natural daylight can be used ‘year-round’ by delivering a timed dose...