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2 LITTERATURE REVIEW In “Lighting and Human Performance II: Beyond Visibility Models Toward a Unified Human Factors Approach to Performance” chapter 5-5, Boyce et al reviews “the factors determining the effectiveness of light exposure” and 5-6 “the consequences of trying to work in circadian night”. (Boyce and M.Rea, 2001) Linking illuminance levels to Melatonin depression. Significant results from Zeitler et al, 2000 showed surprising results in this matter, by indicating that 90% stimulus can be experienced at an illuminance of about 550lx. But half the saturation response is found at exposure to about only 100lx. In figure 8, the phase-shift delay in 3lx exposure shows little to no delay, 11% Melatonin suppression. As expressed, the exposure to dim light 106lx resulted in 88% suppression, while 9100lx resulted in total suppression of 98%, while the shifts of -1,8 is nearly half of the experienced shift of -3,2 in the brightest light condition. (Figure 8) (Zeitzer et al., 2000) A threshold for minimum phase-shift is needed, but Melatonin segregation is clearly effect- ed by illuminance even in exposure to dim light. 2.6.6 Blue light Blue light is a term of speech with no specific definition, other than the suppression on the production of Melatonin in the brain. In the electromag- netic spectrum, a small portion is visible to the human eye, from about 390- 700nm. Blue light is situated from 450-495nm (606-668THz) also known as short wavelength light. As light with shorter wavelength has proved to be more effective than longer wavelengths in suppressing nocturnal melatonin, the term Blue Light is popularly known from resent findings connecting sleep to the use of smart phones, computers and tablets, as such devices emit optical radiation at short wavelengths, very close to peak sensitivity of Melatonin suppression. Even causing effect on some blind patients. (Czeis- ler et al., 1995) The resent use of LED light (Bauer et al., 2017) introduced a new circadian regulator to offices, health care facilities and schools, as the peak in short wavelength light is higher in LED’s than they are composed by RGB light. Compared to incandescent and fluorescent tubes they have a much higher peak in blue light as figure 9 with Spectral Power Distribution (SPD) spans illustrate. (#Figure 9) (Natural light is fundamentally different than artificial light - Sunlight Inside, no date) The duration of exposure was compared to light level in a study by Wood B. et al. suggesting that the effect on nocturnal Melatonin levels from self-il- Figure 9, spectral distribution of artificail light sources compared to natural daylight, (Natural light is fundamentally different than artificial light - Sunlight Inside, no date) Master thesis · MSc Lighting Design · Pernille Bech-Larsen · Fall 2017 28PDF Image | Healing with light
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