A Light Intensity Meter to Measure Plant Growth Conditions


The Project

This project is an investigation into the effect of light intensity on the health of plants and people, or more specifically, gardens and gardeners.

I have spent my life moving back and forth between the north of the UK and the south, and even as far as France, and I have always been puzzled about the incredible effect that geographical location has on plant growth in my gardens, and on the physical health of myself and my friends.

As a child, I moved from Glasgow to Paris and back before the age of 9 and was acutely aware of the changes that I saw my own physiology and on the plant life around me. This same observation held every time I visited Scotland as an adult, through verious seasons and changes of weather, and then reversed as I returned to work in the south. In recent years, as my community and I have matured, I have become aware that certain more serious health problems are more common in the north, and that these are almost certainly brought on partly by lack of sun exposure. At the same time, I have now become a garden owner myself. I now struggle daily with very different gardening challenges in the south, from those of my garden-owning friends in the north.

Throughout this process, I have noticed that gardeners and dog walkers seem disproportionately insulated from the health problems associated with northern living. This is presumably because their hobbies force them outside every day, regardless of the weather.

I know that the difference in human health and plant life, between north and south, is almost certainly to do with light levels. However, I am constantly frustrated by my own inability to accurately measure light intensity with my own eyes. I feel that if I could properly judge how much sunlight I have had in each day, I could make sure to get enough, and teach others to do the same. I would then also be far better able to judge which spots would give a good home to which plant species in my garden. However, this is not an easy call to make.

The difficulty in judging light intensity is caused by the accommodation of the pupil of the eye. The pupils adjust naturally to light intensity. Therefore in any given situation, there seems to be just enough light. The very adaptability of the human being to living in any light intensity, makes it just a little harder for us to live really well, in any light intensity.

My hope in this project is to build a light meter that will enable me to accurately measure how much light there is in my environment in a range of different situations and at different times of day and year. My hope is that this will better enable me to manage my own physiology and also my own garden, with much less guesswork. I am living in Cambridge, but I am helped in the project by my life-long friend Catriona Ferris, who lives in the west of Scotland. She is going to take matching readings to investigate the light intensity in her own environment. Catriona and I are both keen gardeners and we have already investigated and compared most of the other growing conditions in our very different gardens, discussing every detail over facebook. This year we will investigate light conditions, to try to find insight into how light intensity affects not just our plants, but also our own lives and those of our communities.

The design that I have chosen for the light-meter is built from an Arduino and associated parts. My hope is that if we find really interesting results, then this could be turned into a population-level educational tool. It could perhaps be distributed via a magazine like Gardeners' World Magazine or via a tv program like Springwatch, underpinning a national study of light levels in lives and gardens. That way the keen maker-teenagers of the country could build these machines and educate everybody else around them about the nature of light, and its effect on their gardens and health.


This project produced some very interesting information, particularly at the Cambridge part of the test. The results brought significant quality-of-life improvements for some of the participants.

Our biggest realisation in Cambridge, was that our shortage of sunlight in winter was mainly due to the cold weather, and not the lack of light outside.

In the winter time in Cambridge, there is strong sunlight outside most of the time (about 2000 lux) and it is often dry and cold. Because of the very cold temperatures, we were just not going outside to enjoy the sunshine.

To improve things, we bought some quite hi-tech hiking clothes (fleece lined wind-proof over-trousers, that looked a bit like chinos.) This enabled us to maximise heat retention, and to start spending much more time out of doors. This brought significant benefits to general health, through increased sun exposure, exercise, and social time with neighbours. The benefits also extended to children and other family members who followed suit.

This improvement was in the Cambridge end of the experiment. It was not tested in Scotland, where heavy rain and high humidity makes spending time out of doors in winter much trickier.

At the Cambridge end of the experiment, we also were surprised to realise that eyestrain from computer screen use was partly down to the very low light levels indoors (about 30 lux all year round). This compared with a light level of around 700 lux in the University laboratory. This prompted us to change the lighting arrangements in home office rooms to improve eyestrain, which helped a lot.

One of the biggest surprises in both Cambridge and Fenwick, was about the extreme brightness of summer sunshine. Our light meter would not measure above about 55000 Lux, but for much of the summer the sunlight was right up at this level. This is a huge difference from the 30 lux that we were used to when sitting indoors. The realisation of this huge difference has helped us to balance our sun exposure to avoid burning in summer, and also to avoid the effects of lack of sun exposure in winter.

This experiment was very interesting indeed, and brought tangible benefits particularly to the participants in Cambridge.

The Team

Jennifer Deegan, Department of Plant Sciences, University of Cambridge

Growing and photographing the specimens, and planning and building the system.

Tim Deegan.jpg

Tim Deegan, Computer scientist, CohoData

Computer programs and electronics driving the focus stacking system.

Project Outcomes

Project Report.png

Project Report

Project report and documentation on Github

Ongoing Work

The work is still on-going. It has now branched out into spectral analysis, and the investigation of the effects of exposure to different colours of light. We are particularly looking into the effects of LED light on general health.

Jennifer Deegan is testing different kinds of backlighting in computer monitors. She is also experimenting with DIY building of different kinds of computer monitors to look for different effects on the health of the users.

This work is currently self-funded, and is not being written up for publication either online or in a journal. Jennifer Deegan would be very interested in forming new collaborations for the work to continue, and for it potentially to be published online for the interest of others.