Lighting hygiene, melanopic daylight efficacy ratios and energy efficiency

The second Manchester Workshop recommended minimum daytime eye-level exposures to light, and evening and night-time maximums, in terms melanopic equivalent daylight illuminance (melanopic EDI). In integrative lighting and healthy light hygiene regimes, the evening calls for lights with low melanopic daylight efficacy ratios (melanopic DERs) to realize sufficient illuminance for visual function whilst limiting melanopic EDI. In the daytime, where electric lighting is needed, a higher melanopic DER is desirable. Night -time may be considered an extreme version of evening, with a need for light by exception. It is a matter of social and economic importance that daytime, evening and night -time spectral objectives can each strongly conflict with the use of luminous efficacy to determine how much net positive utility derives from electrical energy and its CO2 footprint. This paper compares LED products, including melanopic engineered lighting systems, it discusses electrical energy efficiency implications and introduces the concept of “melanopic efficacy”

Lighting hygiene, melanopic daylight efficacy ratios and energy efficiency

The second Manchester Workshop recommended minimum daytime eye-level exposures to light, and evening and night-time maximums, in terms melanopic equivalent daylight illuminance (melanopic EDI). In integrative lighting and healthy light hygiene regimes, the evening calls for lights with low melanopic daylight efficacy ratios (melanopic DERs) to realize sufficient illuminance for visual function whilst limiting melanopic EDI. In the daytime, where electric lighting is needed, a higher melanopic DER is desirable. Night -time may be considered an extreme version of evening, with a need for light by exception. It is a matter of social and economic importance that daytime, evening and night -time spectral objectives can each strongly conflict with the use of luminous efficacy to determine how much net positive utility derives from electrical energy and its CO2 footprint. This paper compares LED products, including melanopic engineered lighting systems, it discusses electrical energy efficiency implications and introduces the concept of “melanopic efficacy”

The stimulating effect of bright light on physical performance depends on internal time.

The human circadian clock regulates the daily timing of sleep, alertness and performance and is synchronized to the 24-h day by the environmental light-dark cycle. Bright light exposure has been shown to positively affect sleepiness and alertness, yet little is known about its effects on physical performance, especially in relation to chronotype. We, therefore, exposed 43 male participants (mean age 24.5 yrs ± SD 2.3 yrs) in a randomized crossover study to 160 minutes of bright (BL: ≈ 4.420 lx) and dim light (DL: ≈ 230 lx). During the last 40 minutes of these exposures, participants performed a bicycle ergometer test. Time-of-day of the exercise sessions did not differ between the BL and DL condition. Chronotype (MSF(sc), mid-sleep time on free days corrected for oversleep due to sleep debt on workdays) was assessed by the Munich ChronoType Questionnaire (MCTQ). Total work was significantly higher in BL (median 548.4 kJ, min 411.82 kJ, max 875.20 kJ) than in DL (median 521.5 kJ, min 384.33 kJ, max 861.23 kJ) (p = 0.004) going along with increased exhaustion levels in BL (blood lactate (+12.7%, p = 0.009), heart rate (+1.8%, p = 0.031), and Borg scale ratings (+2.6%, p = 0.005)) in all participants. The differences between total work levels in BL and DL were significantly higher (p = 0.004) if participants were tested at a respectively later time point after their individual mid-sleep (chronotype). These novel results demonstrate, that timed BL exposure enhances physical performance with concomitant increase in individual strain, and is related not only to local (external) time, but also to an individual's internal time

The effect of high correlated colour temperature office lighting on employee wellbeing and work performance

BACKGROUND: The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. METHODS: A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated colour temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated colour temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. RESULTS: Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. CONCLUSION: High correlated colour temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits

Report on the Workshop Use and Application of the new CIE s 026/e:2018, Metrology for ipRGC-influenced responses to light “specifying light for its eye-mediated non-visual effects in humans”

In December 2018, the international standard CIE S 026/E:2018 “CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light” (doi.org/10.25039/S026.2018) was published. This standard defines spectral sensitivity functions, quantities and metrics to describe the ability of optical radiation to stimulate each of the five retinal photoreceptor classes that can contribute, via the melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs), to the retinally mediated non-visual effects of light in humans. This one-hour workshop started with four 10 minute presentations about the standard, followed by a general discussion and questions. The four presentations focused on the following topics:1) Introduction to CIE S 026 and its quantities (Luc Schlangen)2) Demonstration of toolkit (in preparation) to calculate CIE S 026 quantities (Presented by Luc Schlangen on behalf of Luke Price)3) Accounting for field of view (David Sliney)4) ipRGCs and pupil response (Manuel Spitschan

Degradation of biological potency in led light sources with lifetime

This paper investigates the degradation of biological potency in LED light sources over their lifetime. Biological potency refers to the ability of light to generate biological effects, for instance on sleep, mood, and circadian rhythms. Current lifetime metrics for LEDs typically do not consider the biological potency, despite its relevance for human health and well-being. Therefore, we investigate such metrics and explore blue light hazard changes over the lifetime of LEDs.Using a dataset of accelerated aging of LEDs, we show that the melanopic equivalent daylight luminance maintenance decreases faster than lumen maintenance, this effect is smaller in LEDs of 4000K versus 2700K. Over lifetime, the melanopic daylight efficacy ratio also decreases, while the blue light hazard does not significantly increase.Our findings highlight the need to consider changes in biological potency over time in the design and implementation of LED lighting solutions

Degradation of biological potency in led light sources with lifetime

This paper investigates the degradation of biological potency in LED light sources over their lifetime. Biological potency refers to the ability of light to generate biological effects, for instance on sleep, mood, and circadian rhythms. Current lifetime metrics for LEDs typically do not consider the biological potency, despite its relevance for human health and well-being. Therefore, we investigate such metrics and explore blue light hazard changes over the lifetime of LEDs.Using a dataset of accelerated aging of LEDs, we show that the melanopic equivalent daylight luminance maintenance decreases faster than lumen maintenance, this effect is smaller in LEDs of 4000K versus 2700K. Over lifetime, the melanopic daylight efficacy ratio also decreases, while the blue light hazard does not significantly increase.Our findings highlight the need to consider changes in biological potency over time in the design and implementation of LED lighting solutions

Blue-enriched Lighting for Older People Living in Care Homes: Effect on Activity, Actigraphic Sleep, Mood and Alertness

Objective: Environmental (little outdoor light; low indoor lighting) and age-related physiological factors (reduced light transmission through the ocular lens, reduced mobility) contribute to a light-deprived environment for older people living in care homes. Methods: This study investigates the effect of increasing indoor light levels with blue-enriched white lighting on objective (rest-activity rhythms, performance) and self-reported (mood, sleep, alertness) measures in older people. Eighty residents (69 female), aged 86 ± 8 yrs (mean ± SD), participated (MMSE 19 ± 6). Overhead fluorescent lighting was installed in communal rooms (n=20) of seven care homes. Four weeks of blue-enriched white lighting (17000 K ≅ 900 lux) were compared with four weeks of control white lighting (4000 K ≅ 200 lux), separated by three weeks wash-out. Participants completed validated mood and sleep questionnaires, psychomotor vigilance task (PVT) and wore activity and light monitors (AWL). Rest-activity rhythms were assessed by cosinor, non-parametric circadian rhythm (NPCRA) and actigraphic sleep analysis. Blue-enriched (17000 K) light increased wake time and activity during sleep decreasing actual sleep time, sleep percentage and sleep efficiency (p < 0.05) (actigraphic sleep). Compared to 4000 K lighting, blue-enriched 17000 K lighting significantly (p < 0.05) advanced the timing of participants’ rest-activity rhythm (cosinor), increased daytime and night-time activity (NPCRA), reduced subjective anxiety (HADA) and sleep quality (PSQI). There was no difference between the two light conditions in daytime alertness and performance (PVT). Conclusion: Blue-enriched lighting produced some positive (increased daytime activity, reduced anxiety) and negative (increased night-time activity, reduced sleep efficiency and quality) effects in older people

Predicting melatonin suppression by light in humans:Unifying photoreceptor-based equivalent daylight illuminances, spectral composition, timing and duration of light exposure

Light‐induced melatonin suppression data from 29 peer‐reviewed publications was analysed by means of a machine‐learning approach to establish which light exposure characteristics (ie photopic illuminance, five α‐opic equivalent daylight illuminances [EDIs], duration and timing of the light exposure, and the dichotomous variables pharmacological pupil dilation and narrowband light source) are the main determinants of melatonin suppression. Melatonin suppression in the data set was dominated by four light exposure characteristics: (1) melanopic EDI, (2) light exposure duration, (3) pupil dilation and (4) S‐cone‐opic EDI. A logistic model was used to evaluate the influence of each of these parameters on the melatonin suppression response. The final logistic model was only based on the first three parameters, since melanopic EDI was the best single (photoreceptor) predictor that was only outperformed by S‐cone‐opic EDI for (photopic) illuminances below 21 lux. This confirms and extends findings on the importance of the metric melanopic EDI for predicting biological effects of light in integrative (human‐centric) lighting applications. The model provides initial and general guidance to lighting practitioners on how to combine spectrum, duration and amount of light exposure when controlling non‐visual responses to light, especially melatonin suppression. The model is a starting tool for developing hypotheses on photoreceptors’ contributions to light's non‐visual responses and helps identifying areas where more data are needed, like on the S‐cone contribution at low illuminances