Ideal HCL lighting

The right light at the right time helps us to be active and efficient during the day and to find sleep and rest at night

Evolution has geared important biological processes in the human body toward living with a natural day/night cycle. This particularly includes bright light during the day and darkness at night, which is why we need daylight or comparable artificial light as a regulator for our internal clock, just like our ancestors thousands of years ago.

The biological effect of light

What type of light has an impact?

In the past 20 years, fundamental research has led to many insights into human biological rhythms and the biological lighting effects.

Ever since the 1980s it has been a well-known fact that seasonal affective disorder (SAD) in the dark winter months can be treated using bright light with high blue components (cf. Rosenthal et al., 1984; Terman et al., 1995). We owe further insights to research from the last 20 years. Based on current knowledge, the following factors in particular are crucial for the non-visual, biological effect of light on people (see DIN SPEC 67600):

  • The spectral proportion of the light. Light similar to natural daylight with high blue components has the strongest activating effect. This particularly stimulates the receptors in the eye.
  • The intensity of the light. Research results show an activating effect starting at an illuminance level of 250 lux directly at the eye, if the light has a quality similar to natural daylight.
  • The area of the light. Large luminous surfaces that are visible on ceilings or walls intensify the activating effect. They perfectly address the photosensitive ganglion cells in the inferior part of the retina and, thanks to their large surface areas, they reach many of these photoreceptors. This means that large ceiling lights or indirectly illuminated ceilings can simulate the natural sky.
  • The brightness levels during the day and at night. A big difference between day and night supports our circadian rhythm and hence also sleep.
The ideal HCL lighting

What would be an ideal HCL lighting?

Lighting based on the latest scientific findings that addresses the needs of people is defined as “human centric lighting” (HCL).

When planning an ideal HCL concept, both the visual effects of light (for better vision) and the non-visual biological effects of light must be taken into account. Generally, the following principles apply:

  • The more natural light that is used, the better.
  • Smart HCL solutions should automatically be oriented to the changes in natural daylight in terms of light colors, brightness and the spatial distribution of the light.
  • People are especially receptive to the biological effects of light in the first two hours after getting up and at least two hours before bedtime.
  • Large lights from above that imitate a sunlit (blue) sky have the greatest biologically activating effect. Therefore, at the start of the day until lunch time and after the lunch break, bright, cold white light with a high blue component (such as 6500 Kelvin at an illuminance of 300 lux at the eye) should be used. Indirect light which includes both ceilings and walls is ideal for this.
  • Towards the evening the lighting should be changed to direct warm white light without blue components (such as 2700 to 3000 kelvin) to help our bodies to relax and prepare for the night.
Benefits of HCL

Business and economic benefits of HCL

The most significant economic benefits of HCL are in the industry segments

In the study published in 2015 titled “Quantified Benefits of Human Centric Lighting”, international management consultancy A.T. Kearney illustrated the financial benefits resulting from the use of HCL from a business and economic point of view

All the calculations for the different areas of application were based on the comparison of a conventional high-quality LED solution with a lighting system that meets the criteria of human centric lighting. In HCL lighting, the visual and biological needs of people are taken into account. Seven indoor applications were selected for analysis: industry (repetitive), industry (advanced), office, education, medical, residential (elderly care) and residential (homes). The results are available on the websites of the associations.

HCL has higher energy requirements than an LED solution designed for visual purposes only. To achieve the desired biological effect, higher illuminance levels and blue components in the light are needed in some places. However, if HCL is compared with an older conventional lighting system as part of an upgrade, there will be energy savings (not calculated in this study). The additional costs of installing HCL lighting were not calculated. The study focused on the financial benefits of HCL compared with the necessary annual energy costs of the lighting system.

Business benefits
The most significant micro benefits of HCL can be found in the industrial segments. This is proven by previous studies which relate above all to projected productivity gains. When it comes to hospitals and care homes for the elderly, the operator often cannot leverage the entire potential alone. There are financial benefits through cost savings – including for insurance companies for example.

Economic benefits
All the areas of application are also looked at in more detail and quantified in the study at macro level. The assumptions on market penetration by 2020 are based on an estimate published in an earlier HCL study that the European market for HCL may be 1.4 billion euros by 2020. According to projections by A. T. Kearney, the benefits for Europe may be up to 870 million euros in 2020 for a realistic market penetration. 527 million thereof is extrapolated based on scientific studies which have already been carried out. The study comes to the conclusion that in most segments it is the owners and investors who benefit most. But there are also additional advantages in terms of social benefits that justify the additional expense for HCL. In the case of theoretical full market penetration with HCL in all areas of application, the study suggests a potential macro benefit of up to 12.8 billion euros for Europe.

Human Centric Lighting in various application areas