Today is the vernal equinox, and traditionally marks the beginning of Spring. It’s also when daytime and night-time are of approximately equal duration.
This has resonance with our (artificial) experimental set-up of day:night (dark:light) for our plants growing in environmentally controlled cabinets. When we present our circadian data we would typically denote ‘the day’ on our slides or papers as white and black bars denoting day and night, respectively.
I suppose today is the day we should be doing our experiments in Nature instead of the growth cabinets…
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Often we need to measure light intensity for our experiments and we use this little gizmo to do the job – a LI-COR light meter. Measuring light intensity is quite complex, but I find this explanation from GroWell (Hydroponics & Lighting) to be very useful:
Photons are counted in micromoles (µmol). One µmol is 602 quadrillion photons! I can’t even imagine a quadrillion!
I took a measurement of outdoor light intensity in Glasgow in February – reasonably bright, fast moving clouds, occasional cloud cover, temperature around 4oC. As you can see there were around 160 x 602 quadrillion photons hitting the sensor per second.
When there was no cloud I got readings up to around 600 umol – light intensity really does rapidly change….moving to the shade of a building I recorded around 45umol
When we grow our plants in environmentally controlled growth cabinet we set the light intensity to around 130-150 mol. I suppose this is equivalent to a reasonably cloudy day in Glasgow! Plants will be used to much higher levels of light intensity though….how do they adapt to such rapid shifts in light?