Nightingale, Florence, Notes on Nursing: What It Is and What It Is Not, London: Harrison, 1960
Second only to fresh air … I should be inclined to rank light in importance for the sick. Direct sunlight, not only daylight, is necessary for speedy recovery … I mention from experience, as quite perceptible in promoting recovery, the being able to see out of a window, instead of looking against a dead wall; the bright colours of flowers; the being able to read in bed by the light of the window close to the bed-head. It is generally said the effect is upon the mind. Perhaps so, but it is not less so upon the body on that account …
Florence Nightingale, 1860
We need light for vision, plants need light for energy.
Aspects of daylighting that have been shown to be beneficial include sunlight, skylight, changing of colour temperature through the day, and the associated external views
Good building design will maximise the natural environment to minimise energy consumption.
The overlapping of the light spectrum for people and plants is a compelling reason why appropriate design consideration should be given to provide the “right” light for people and plants, with little, if any, additional cost implications.
People and plants both need “blue” light. We now have a better understanding of the effects of light on the health and wellbeing of building occupants. Lighting design in North America and Europe is being extended beyond the normal parameters.
This stems from recent research that compares the effects of health, wellbeing and alertness of people working under different lighting conditions and shows that the biological effect of light is not directly stimulated by the illuminance on the working plane, but by light entering the eye. In other words light needs to enter the eye directly.
There are also photoreceptors in the eye (in addition to the rods and cones) that control the production of the hormones melatonin and cortisol. While melatonin makes us sleepy and relaxed, cortisol makes us feel awake, alert and alive.
The peak sensitivity for the visual system or photopic vision, which stimulates the production of either melatonin or cortisol, occurs at 550 nanometres (or the green light part of the light spectrum) while the peak sensitivity of the circadian system is at the short wavelength region of the spectrum at 420 – 480 nm, that is blue light, which is also essential for healthy plant growth.
The Circadian Response , which regulates the biological system, is firmly in the blue part of the spectrum, which is also essential for stimulating chlorophyll production, encouraging strong stems and leaves and compact vegetative growth.
So both people and plants need blue light. Recognised by Florence Nightingale 156 years ago.
What we know
Light is the major determining factor in successfully maintaining healthy plants indoors. Incorrect lighting can result in interior landscape projects achieving limited success, or invariably failure, with possible negative impact on reputation and economic consequences.
When the light requirements are not met, the design concept of bringing nature indoors to create a healthy workspace will not be achieved. For this reason it is crucial before installation to Identify the available daylight, daily light integral, and spectral characteristics of the glazing, for selection of appropriate plant species. Meeting the correct light requirements allows planning for success.
Lighting for good plant health and human health indoors requires a careful evaluation of all of the factors. Getting it right ensures thriving interior landscapes, and a more healthful and productive environment.