WHAT IS LIGHT ?

THE LIGHTING HANDBOOK – CHAPTER 1

Light is that part of the electromagnetic spectrum that is perceived by our eyes. The wavelength range is between 380 and 780 nm. The cones come on during the day and we see colours, whereas at night the rods take over and we only see shades of grey.

1. What is the melanopic effect of light?

The retina also contains photosensitive ganglion cells. These are sensitive to blue light and suppress the sleep hormone melatonin at night. Melatonin is responsible for a good sleep at night. Suppressing melatonin in the morning helps keep you awake during the day. This means that the right light controls the circadian rhythm thus a healthy waking and sleeping behaviour.

2. What does the human eye see?

Explanation of the three curves:

V(λ) = Perception of brightness, daytime seeing with the cones

V'(λ) = Night-time seeing with the rods

Smel(λ) = Melatonin suppression with the photosensitive ganglion cells

3. Human Centric Lighting

Human Centric Lighting (HCL) expresses the positive effect of light and lighting on the health, well-being and performance of humans and thus has both short and long-term benefits.

Light has a triple effect

Light for visual functions

– Illumination of task area in conformity with relevant standards

– Glare-free and convenient

Light for emotional perception

– Lighting enhancing architecture

– Creating scenes and effects

Light creating biological effects

– Supporting people’s circadian rhythm

– Stimulating or relaxing