Putting it into practice

Ben proving it is possible to read by bioluminescent light

We wanted to provide some proof of concept of these ideas. We built the bacterial bubble lamp to investigate this, and also read the Jungle Book using a flask containing E. coli expressing our bacterial luciferase.

We had thought about bacteria being used for emergency lighting, and our advisor Fernan printed a fire exit sign, which was placed over a plate containing one of our strains of E. coli. In a real system we would imagine using anhydrobiosis to create bacteria 'in hibernation' which could be activated when needed.

Modelling

Figure 1: The solar radiation spectrum for direct light at both the top of the Earth's atmosphere and at sea level.

Figure 2: The emission spectrum of V. Fischeri (shown in black)

Figure 3: Photopic (black) and scotopic (green) luminosity functions.

Figure 4: The formula for calculating luminance. (F:Luminous Flux, y:Luminosity Function,J:Spectral Power Distribution,λ:Wavelength

To show that it may one day indeed be possible to have bioluminescent trees replacing street lamps we considered how efficicient the plants would have to be in order to match a low-intensity street lamp.

Figure 1 shows the radiation spectrum recieved from the sun at sea level. In total this gives about 1,321 – 1,413 W/m² of radiant energy for regions in North America. (Data supplied by American Society for Testing and Materials (ASTM) Terrestrial Reference Spectra, a common standard used in photovoltaics).

This is a lot of energy, but of course most of it is not accessible to plants. They can only absorb in the visible region (corresponding to roughy 45% of total solar energy), radiation known as PAR (photosynthetically active radiation). In addition, there are other constraints, such as reflectivity of leaves and the absorption spectrum of chlorophyll. The net result is that in general plants are only able to take between 3 and 6% of total solar radiation, corresponding to roughly 60 W/m² (Figures from Hall, D.O. and House, J.I., Biomass and Bioenergy, 6,11-30 (1994).)

That's what plants have available to them, we then considered what they need to be putting out in order to function as street lights.

1,413 – 1,321W/m² "Chapter 8 – Measurement of sunshine duration" (PDF). CIMO Guide. World Meteorological Organization. http://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/CIMO%20Guide%207th%20Edition,%202008/Part%20I/Chapter%208.pdf. Retrieved 2008-12-01.