Circadian Rhythm Sample

The ALPHABET Human Centric Series features Sunlike®, the first LED light source that most closely mimics the full spectrum of natural daylight.

  • Advanced material and packaging technology developed by Seoul Semiconductor and Toshiba Materials
  • Fills the “green gap” from traditional LED lighting
  • Spectral output designed to minimize exposure to shorter blue light wavelengths
  • Color Rendering Index >97 to maximize natural hues and saturation
  • Available in 2700K, 3000K, 3500K, 4000K, and 5000K CCT


The human circadian system is the body’s natural clock that affects critical functions including the production of testosterone, growth hormone, cortisol, and melatonin. These hormones have a direct influence on the body’s overall functionality in key areas including:

  • Sleep
  • Cognition
  • Performance
  • Alertness
  • Metabolism


Light is formally defined as optical radiation capable of providing visual sensation in humans. However, light also produces non-visual physiological responses that are unrelated to spatial patterns of light exposure. Scientists have discovered a photopigment called melanopsin in special photosensitive cells in the eye’s retina, in addition to rods and cones, which are part of the visual system. These cells, known as ipRGCs, form the main neural conduit to the suprachiasmatic nuclei (SCN) in the part of the brain where our circadian clock is located.

Circadian phototransduction is the process that converts light received by the three photoreceptors (rods, cones and ipRGCs) in the retina into electrical signals in the SCN. Both light and dark set the timing of the SCN, and disruption of this clock has been shown to negatively affect many health outcomes. The SCN control the release of melatonin, which is a hormone produced under conditions of darkness, normally at night. The spectral sensitivity of the SCN, as measured by acute melatonin suppression by light at night, peaks at approximately 460 nm.

chart brain
chart typical LED
Chart Human Centric


While there is no official standard defining the impact of light on the circadian system, as recognized by international standards organizations, there are two metrics proposed by the Lighting Research Center (LRC).

The first is circadian light, which is irradiance weighted by the spectral sensitivity of the phototransduction mechanisms that stimulate the biological clock, as measured by nocturnal melatonin suppression. This term is comparable to illuminance, which is spectrally weighted irradiance for the human visual system. The second metric is circadian stimulus, which is a transformation of circadian light into relative units on a scale from zero (no suppression) to 0.7 (saturation). It is directly proportional to nocturnal melatonin suppression after one hour of light exposure from zero to 70 percent. The threshold for circadian activation is approximately 0.1.

When specifying this stimulus, one must account not only for the quantity of circadian light, but also factor in the duration and time of day. Research has shown that higher exposure to light during the day will lower the sensitivity of the circadian system to light at night. LRC studies have shown that high CS values (CS>0.3) in the morning together with low CS values (CS~0.1) at night help people sleep better at night and feel better during the day.

ALPHABET Human Centric Lighting, featuring Sunlike, is RG-1 Eye Safety Rated which is the FIRST 25W COB package ever to receive the certification, and is the second lowest risk possible. The governing body is International Commission on Illumination. What is CIE S009/2002 Eye and Skin Safety Certification?

Eye Safety Certification refers to the standard adopted (CIE S 009:2002) by the International Commission on Illumination which defines the safety limits for the eyes and skin. The relevant standard is defined in IEC/EN 62471. The assessment of risks to blue light exposure per the standard IEC/EN 62471 began to apply to lighting systems using LEDs from September 1st, 2009.

Risk Classification Table

Risk Group Risk
No Risk (Exempt) No photobiological risk
RG 1 (Low Risk) No photobiological risk in normal daily life
RG 2 (Intermediate Risk) Doesn’t cause risk but feels unpleasant due to heat produced from bright light
RG 3 (High Risk) Dangerous even if a human is exposed to light for an instant