What intuition tells us…

  • Daylight means light quality and naturalness of colors
  • There is nothing comparable to natural sunlight
  • Daylight makes us more adapted and productive
  • Sunlight has a positive effect on mood

Lessons learned in the Hi-LED project with our spectrally-tunable LED modules:

Ledmotive can reproduce exactly, the physical properties of daylight, in the visible range

We have demonstrated that the spectrum of light can be tuned to optimize people’s alertness levels, performance, and mood, depending on the time of day and the task required. Wireless feedback from wearable biosensors enables the output of the light engine to be controlled directly by people’s physiological state (e.g. heart rate, heart rate variability, and skin surface temperature), maximizing or minimizing the alerting effects of light as necessary.

  • In more detail: The ability to sculpt the spectrum of light with the tuneable multi-LED-channel light engine in real-time allows us to selectively stimulate the visual and non-visual pathways. The non-visual pathway responds best to light of short wavelengths, via the photopigment melanopsin expressed by the intrinsically photosensitive retinal ganglion cells. The visual brightness and chromaticity (“colour”) of light is determined by the cone photoreceptors. We developed methods to generate variable light spectra with the tuneable light engine, which allow us to trade off the amounts and effects of non-visual (“melanopic”) and visual (“photopic”) illuminance.
  • We have shown that (1) narrow-band “blue” light, at low photopic illuminance, suppresses melatonin levels as effectively as broad-band “white” light with the same melanopic illuminance but much higher photopic illuminance; (2) broad-band “white” light suppresses melatonin levels much more effectively than “amber” light at the same photopic illuminance; (3) “white” light suppresses subjective sleepiness equally effectively as “blue” light with the same melanopic illuminance, and much more than “amber” light. But, although “blue” and “white” light both suppress melatonin and reduce sleepiness, they do not reduce the effects of fatigue on performance in the evening. Instead, “amber” light increases performance on visual attention tasks. “Amber” light, with low melanopic illuminance and high photopic illuminance, is also rated as more pleasant than “blue” light. Thus, we recommend that, in the evening, to improve mood and visual performance, while allowing melatonin levels to rise naturally, “amber” light with high photopic illuminance but low melanopic illuminance is used.
  • We have demonstrated that the light engines can be controlled wirelessly in real-time by the data from wearable biosensors – actigraphs – which is used to monitor people’s alertness levels during the “post-lunch dip” in the afternoon. We have shown that changes in light spectra can be triggered automatically when alertness levels decline, and that the resulting increase in photopic or melanopic illuminance does boost alertness.
  • The ability to tune light spectra in real-time with multi-channel LED technology allows teasing apart of the visual and non-visual effects of light, and their dependence on the shape of the illumination spectral power distribution. From a series of behavioural experiments in people at different times of day, performing different tasks, we conclude that “Seeing worse may lead to feeling worse and performing worse, despite being less sleepy.”
  • Overall conclusion: Lighting technology in the home and workplaces may soon be modulated in real-time to individual needs, based on data from wearable biosensors, and dependent on circadian rhythm and environment.

“The impact of lighting (and, above all, spectrally-tunable lighting) on our health will soon have an important role in lighting designs that so far have been solely based on energy efficiency considerations, not only because it will be beneficial to humans, but also because the return on investment in terms of well-being and productivity will certainly pay off”.

Dr. Josep Carreras, PhD.


More scientific evidence: http://www.hi-led.eu

The scientific facts behind the intuition

The following research findings on the influence of light on our sleep/wake cycle are particularly noteworthy:

  1. Production of melatonin, the hormone that helps to induce sleepiness and that regulates our sleep/wake cycle, is directly impacted by light1,2,3,4. (Not only is affected by natural light but also by artificial light)
  2. By itself, our natural body clock typically runs with an average period of 24h and 15 to 30 min5,6,7,8 so somewhat longer than our artificial 24h clocks. Unless reset, this will make us want to go to bed later causing us to be more dependent on our alarm clocks in the morning.
  3. Light with the right quality and timing can reset the half-hour lag and re-synchronize our body clock with our artificial 24h clocks9,10,11,12.
  4. Morning light is very powerful in adjusting our body clock13,14,15,16 and artificial light that mimics bright daylight is highly effective at regulating and synchronizing our sleep/wake cycle.
  5. Light is key to overcoming both jet lag17 and “social jet lag” (the “Monday morning blues” feeling).
  6. Light influences our mood18,19,20,21,22,23,24 and reinforces a good sleep/wake cycle, thus contributing to our overall health and well-being.

Scientific references

  1. Santhi N, Thorne HC, van der Veen DR, Johnsen S, Mills SL, Hommes V, Schlangen LJM, Archer SN, Dijk DJ (2011) The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans. J Pineal Res 53: 47-59. 10.1111/j.1600-079X.2011.00970.x [doi].
  2. Mishima K, Okawa M, Shimizu T, Hishikawa Y (2001) Diminished melatonin secretion in the elderly caused by insufficient environmental illumination. J Clin Endocrinol Metab 86: 129-134.
  3. Czeisler CA, Shanahan TL, Klerman EB, Martens H, Brotman DJ, Emens JS, Klein T, Rizzo JF, III (1995) Suppression of melatonin secretion in some blind patients by exposure to bright light. N Engl J Med 332:6-11.
  4. J. M. Zeitzer, D. J. Dijk, R. Kronauer, E. Brown, and C. Czeisler. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J.Physiol 526 Pt 3:695-702, 2000.
  5. M. A. Carskadon, S. E. Labyak, C. Acebo, and R. Seifer. Intrinsic circadian period of adolescent humans measured in conditions of forced desynchrony. Neurosci.Lett. 260 (2):129-132, 1999.
  6. T. L. Kelly, D. F. Neri, J. T. Grill, D. Ryman, P. D. Hunt, D. J. Dijk, T. L. Shanahan, and C. A. Czeisler. Nonentrained circadian rhythms of melatonin in submariners scheduled to an 18-hour day. J.Biol.Rhythms 14 (3):190-196, 1999.
  7. C. A. Czeisler, J. F. Duffy, T. L. Shanahan, E. N. Brown, J. F. Mitchell, D. W. Rimmer, J. M. Ronda, E. J. Silva, J. S. Allan, J. S. Emens, D. J. Dijk, and R. E. Kronauer. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science284 (5423):2177-2181, 1999.
  8. S. A. Brown, F. Fleury-Olela, E. Nagoshi, C. Hauser, C. Juge, C. A. Meier, R. Chicheportiche, J. M. Dayer, U. Albrecht, and U. Schibler. The Period Length of Fibroblast Circadian Gene Expression Varies Widely among Human Individuals. PLoS.Biol. 3 (10):e338, 2005.
  9. S. W. Lockley, G. C. Brainard, and C. A. Czeisler. High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light. J.Clin.Endocrinol. Metab 88 (9):4502-4505, 2003.
  10. J. M. Zeitzer, D. J. Dijk, R. Kronauer, E. Brown, and C. Czeisler. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J.Physiol 526 Pt 3:695-702, 2000.
  11. C. Gronfier, K. P. Wright, Jr., R. E. Kronauer, M. E. Jewett, and C. A. Czeisler. Efficacy of a single sequence of intermittent bright light pulses for delaying circadian phase in humans. Am.J.Physiol Endocrinol.Metab 287(1):E174-E181, 2004.
  12. R. P. Najjar, L. Wolf, J. Taillard, L. J. Schlangen, A. Salam, C. Cajochen, and C. Gronfier. Chronic artificial blue-enriched white light is an effective countermeasure to delayed circadian phase and neurobehavioral decrements. PLoS.ONE. 9 (7):e102827, 2014.
  13. N. E. Rosenthal, J. R. Joseph-Vanderpool, A. A. Levendosky, S. H. Johnston, R. Allen, K. A. Kelly, E. Souetre, P. M. Schultz, and K. E. Starz. Phase-shifting effects of bright morning light as treatment for delayed sleep phase syndrome. Sleep 13 (4):354-361, 1990.
  14. M. Terman, A. J. Lewy, D. J. Dijk, Z. Boulos, C. I. Eastman, and S. S. Campbell. Light treatment for sleep disorders: consensus report. IV. Sleep phase and duration disturbances. J.Biol.Rhythms 10(2):135-147, 1995.
  15. V. L. Revell, T. A. Molina, and C. I. Eastman. Human Phase Response Curve to Intermittent Blue Light Using a Commercially Available Device. J.Physiol., 2012.
  16. S. B. Khalsa, M. E. Jewett, C. Cajochen, and C. A. Czeisler. A phase response curve to single bright light pulses in human subjects. J.Physiol 549 (Pt 3):945-952, 2003.
  17. Z. Boulos, S. S. Campbell, A. J. Lewy, M. Terman, D. J. Dijk, and C. I. Eastman. Light treatment for sleep disorders: consensus report. VII. Jet lag. J.Biol.Rhythms 10 (2):167-176, 1995.
  18. T. Partonen and J. Lonnqvist. Bright light improves vitality and alleviates distress in healthy people. J.Affect.Disord. 57 (1-3):55-61, 2000.
  19. G. W. Lambert, C. Reid, D. M. Kaye, G. L. Jennings, and M. D. Esler. Effect of sunlight and season on serotonin turnover in the brain. Lancet 360 (9348):1840-1842, 2002.
  20. M. Aan Het Rot, D. S. Moskowitz, and S. N. Young. Exposure to bright light is associated with positive social interaction and good mood over short time periods: A naturalistic study in mildly seasonal people. J Psychiatr. Res, 2007.
  21. A. Tuunainen, D. F. Kripke, and T. Endo. Light therapy for non-seasonal depression. Cochrane. Database.Syst.Rev. (2): CD004050, 2004.
  22. R. N. Golden, B. N. Gaynes, R. D. Ekstrom, R. M. Hamer, F. M. Jacobsen, T. Suppes, K. L. Wisner, and C. B. Nemeroff. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. Am.J.Psychiatry 162 (4):656-662, 2005.
  23. A. Wirz-Justice, F. Benedetti, and M. Terman. Chronotherapeutics for Affective Disorders : A Clinician’s Manual for Light and Wake Therapy, Basel:Karger, 2009.
  24. White Paper: “The effect of light on our sleep/wake cycle”, by Luc Schlangen, principal scientist at Philips