Evaluation of the effects of blue-enriched white light on cognitive performance, arousal, and overall appreciation of lighting.

Introduction: Light's non-visual effects on the biological clock, cognitive performance, alertness, and mental health are getting more recognized. These are primarily driven by blue light, which triggers specific retinal cells containing melanopsin. Traditionally, research on light has relied on correlated color temperature (CCT) as a metric of its biological influence, given that bluer light corresponds to higher Kelvin values. However, CCT proves to be an inadequate proxy of light's biological effects. A more precise metric is melanopic Equivalent Daylight Illuminance (mel-EDI), which aligns with melanopsin spectrum. Studies have reported positive cognitive impacts of blue-enriched white light. It's unclear if the mixed results are due to different mel-EDI levels since this factor wasn't assessed. Method: Given recent recommendations from experts to aim for at least 250 mel-EDI exposure daily for cognitive benefits, our aim was to assess if a 50-minute exposure to LED light with 250 mel-EDI could enhance concentration and alertness, without affecting visual performance or comfort compared to conventional lighting producing around 150 mel-EDI. To ensure mel-EDI's impact, photopic lux levels were kept constant across conditions. Conditions were counterbalanced, parameters included subjective sleepiness (KSS; Karolinska Sleepiness Scale), concentration (d2-R test), visual performance (FrACT; Freiburg Visual Acuity and Contrast Test), general appreciation (VAS; Visual Analogous Scale), preferences and comfort (modified OLS; Office Lighting Survey). Results: The experimental light significantly reduced sleepiness (p = 0.03, Cohen's d = 0.42) and also decreased contrast sensitivity (p = 0.01, Cohen's d = 0.50). The conventional light was found to be more comfortable (p = 0.002, Cohen's d = 0.62), cheerful (p = 0.02, Cohen's d = 0.46) and pleasant (p = 0.005, Cohen's d = 0.55) while the experimental light was perceived as brighter (p = 0.004, Cohen's d = 0.58) and tended to be more stimulating (p = 0.10). Notably, there was a preference for conventional lighting (p = 0.004, Cohen's d=0.56) and concentration was equally improved in both conditions. Discussion: Despite the lack of further improvement in concentration from exposure to blue-enriched light, given the observed benefits in terms of vigilance, further research over an extended period would be justified. These findings could subsequently motivate cognitive optimization through lighting for workers that would benefit from artificial lighting such as in northern regions.

[Development of insulin reserves in the first 18 months in the insulin-dependent diabetic with or without remission of insulin-dependence]. / Evolution de la réserve insulinique dans les 18 premiers mois du diabète insulinoprive avec ou sans rémission d'insulinodépendance.

It seems rational to consider that residual insulin secretion is one of the factors which determine the short-term course of inaugural type I diabetes. But what about the mid-term course? We evaluated prospectively the insulin reserve (fasting and post-prandial C peptide) in 52 patients throughout the subsequent development of the disease. The patients (36 men, 16 women, mean age 35 years), who presented with ketonuria and weight loss, received a 10-day course of intensive insulin therapy, after which a remission of insulin dependence was observed in 40 of them (77 per cent). These 40 patients differed from those who had no such remission in that they were heavier and had a better initial insulin secretion. There was no significant difference between the two groups with regards to immunogenetic markers (presence of anti-islet antibodies 28/35 vs 8/12, DR3 and/or DR4 tissue group 27/37 vs 8/10). Following intensive insulin therapy, the C peptide value was consistently increased. At 6, 12 and 18 months the insulin secretion in patients of the remission group remained stable and always higher than that of patients who did not have a remission and whose insulin secretion collapsed at 18 months. Another characteristic of the remission group was that C peptide secretion could be stimulated by meals throughout the follow-up period (post-prandial C peptide at 18 months: 0.63 nmol/l). It is concluded that residual insulin secretion is one of the most effective predictive factors of remission when type I diabetes is first diagnosed and remains stable for the first 18 months of the disease in patients who show a remission.