Sunlight brightness not needed for circadian rhythm? (lightbulb brightness can be enough?)

cs3000

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Probably best to assume sunlight brightness is optimal for circadian rhythm still, (faster effects at that brightness?), but studies have shown light from standard lightbulbs give significant effects on circadian rhythm still, especially if around 500 lux which looks to give full effects in magnitude equivalent to outdoor sunlight brightness 10,000 lux

Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression

Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression - PubMed

Ocular exposure to early morning room light can significantly advance the timing of the human circadian pacemaker. The resetting response to such light has a non-linear relationship to illuminance. The dose-response relationship of the human circadian pacemaker to late evening light of dim to moderate intensity has not been well established.
Twenty-three healthy young male and female volunteers took part in a 9 day protocol in which a single experimental light exposure6.5 h in duration was given in the early biological night. The effects of the light exposure on the endogenous circadian phase of the melatonin rhythm and the acute effects of the light exposure on plasma melatonin concentration were calculated.
We demonstrate that humans are highly responsive to the phase-delaying effects of light during the early biological night and that both the phase resetting response to light and the acute suppressive effects of light on plasma melatonin follow a logistic dose-response curve, as do many circadian responses to light in mammals. Contrary to expectations, we found that half of the maximal phase-delaying response achieved in response to a single episode of evening bright light (approximately 9000 lux (lx) can be obtained with just over 1 % of this light (dim room light of approximately 100 lx). The same held true for the acute suppressive effects of light on plasma melatonin concentrations. This indicates that even small changes in ordinary light exposure during the late evening hours can significantly affect both plasma melatonin concentrations and the entrained phase of the human circadian pacemaker.

lux.jpg



This study shows even a dimly lit room of 100 lux significantly works on circadian rhythm, giving half the effect that 9000 lux does (outdoor light). [most rooms with the light on are probably 200+ lux and most offices are probably 300 lux or 500 lux].


If you look on the images it tells you from the data plotted "Saturation of the phase-shift response is predicted to occur with ∼550 lx and saturation of the melatonin-suppression response is predicted to occur with ∼200 lx."


"A laboratory study by Aoki et al. evaluated the minimum amount of light that is required to suppress nocturnal melatonin by exposing five subjects to light levels ranging from < 10 to 5000 lux of cool-white fluorescent light. 40 The results showed that for exposure durations of 30, 60, 90 and 120 minutes, the minimum amount of light needed to significantly suppress melatonin was 393, 366, 339 and 285 lux respectively". Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness <- More duration = less lux for effect


So basically if you don't get much morning sunlight but spend your days mostly in rooms with the lightbulb on you are still getting significant impact on your circadian rhythm. If the rooms you're in are ~500lux you're getting the same impact as outdoor sunlight brightness in magnitude (can measure with device, or maybe a phone app if they're accurate?).
Probably best to assume sunlight brightness is optimal for circadian rhythm still, (faster effects at that brightness?), but studies have shown light from standard lightbulbs give significant effects on circadian rhythm still, especially if around 500 lux which looks to give full effects in magnitude equivalent to outdoor sunlight brightness 10,000 lux

Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression

Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression - PubMed

Ocular exposure to early morning room light can significantly advance the timing of the human circadian pacemaker. The resetting response to such light has a non-linear relationship to illuminance. The dose-response relationship of the human circadian pacemaker to late evening light of dim to moderate intensity has not been well established.
Twenty-three healthy young male and female volunteers took part in a 9 day protocol in which a single experimental light exposure6.5 h in duration was given in the early biological night. The effects of the light exposure on the endogenous circadian phase of the melatonin rhythm and the acute effects of the light exposure on plasma melatonin concentration were calculated.
We demonstrate that humans are highly responsive to the phase-delaying effects of light during the early biological night and that both the phase resetting response to light and the acute suppressive effects of light on plasma melatonin follow a logistic dose-response curve, as do many circadian responses to light in mammals. Contrary to expectations, we found that half of the maximal phase-delaying response achieved in response to a single episode of evening bright light (approximately 9000 lux (lx) can be obtained with just over 1 % of this light (dim room light of approximately 100 lx). The same held true for the acute suppressive effects of light on plasma melatonin concentrations. This indicates that even small changes in ordinary light exposure during the late evening hours can significantly affect both plasma melatonin concentrations and the entrained phase of the human circadian pacemaker.

lux.jpg



This study shows even a dimly lit room of 100 lux significantly works on circadian rhythm, giving half the effect that 9000 lux does (outdoor light). [most rooms with the light on are probably 200+ lux and most offices are probably 300 lux or 500 lux].


If you look on the images it tells you from the data plotted "Saturation of the phase-shift response is predicted to occur with ∼550 lx and saturation of the melatonin-suppression response is predicted to occur with ∼200 lx."


"A laboratory study by Aoki et al. evaluated the minimum amount of light that is required to suppress nocturnal melatonin by exposing five subjects to light levels ranging from < 10 to 5000 lux of cool-white fluorescent light. 40 The results showed that for exposure durations of 30, 60, 90 and 120 minutes, the minimum amount of light needed to significantly suppress melatonin was 393, 366, 339 and 285 lux respectively". Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness <- More duration = less lux for effect


So basically if you don't get much morning sunlight but spend your days mostly in standard lit rooms with the lightbulb on you are probably getting less impact but still largely significant impact on your circadian rhythm. If the rooms you're in are ~500lux you're getting the same impact as outdoor sunlight brightness in terms of magnitude (can measure with device, or maybe a phone app if they're accurate?). but not sure on timing to reach same magnitude, if it works the same speed as outdoor brightness or not? also could be different impacts if done in the day but seems significant
 

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