Solar Eclipse

Edinburgh, Scotland, Solar Eclipse Friday 20th March 2015

This time last week the Earth arrived at its vernal equinox where some of us in the Northern Hemisphere were treated to a rare Solar Eclipse as a Super Moon drifted in-front of the Sun. In a lightly cloudy Edinburgh, Scotland, we managed a 95% partial eclipse revealing a beautiful crescent.

At the same time as I was taking this photo, a south facing prototype Lightlog was quietly sitting on a window shelf enjoying a lovely day’s worth of light data including its own view of the very same eclipse.

The first image below shows a spectrum visualisation of the received light; the image below that is an enhanced colour version using the same data. Notice how the blue day light desaturates around 9:35am as the Moon’s disk (almost) covers the Sun.

Spectrum visualisation on day of Solar Eclipse

Enhanced colour (scaled saturation) visualisation

The ‘spikes’ in the data are caused as the day’s partial cloud cover drifts over the sun, a clear blue day (as viewed from this stationary Lightlog’s south facing window position) would show a beautiful smooth arc between sunrise and sun set.

Visualising Light Data

One of the goals of Lightlog is to help people engage with and reflect on light data they collect over time. Due to its size and power constraints, the physical Lightlog device has a minimal user interface (UI), just enough to display the daily light goal reached, and show if the current illumination is bright enough to be effective towards the daily goal (2,500 lux or above). Lightlog collects much more data than it can display alone, by synchronising to a device with a screen and more computing power, allows a rich, engaging, detailed views of your daily light profile, and the opportunity for additional analysis over the set of collected data.

The primary visualisation is designed around the full colour spectrum composing visible light. It’s an approximation of a full light spectrum as Lightlog records single sample points in the red (~614nm), green (~525nm), and blue (~468nm) frequencies; with a fourth sample unfiltered, capturing as much of the full spectrum energy as possible for lux calculation (an interesting future project could be to use many more sensors across the spectrum frequency to generate a high resolution spectrum with chemical absorption lines). For use with Winter Blues and Seasonal Affective Disorder, the three red, green, blue sensors provide useful information about the frequency of light exposure as some studies have shown shorter wavelength, blue light, is more effective, vs. longer wavelength red light.

Below shows an example image taken from real data displaying several days from November. Notice the relatively long nights and short Scottish days at this time of year.

Example Lightlog data for Nov 28-30

Below is a close-up view of November 30th; note the strong direct sunlight between 12:30 and 13:30, this would have been more than enough for the recommended daily amount of bright light.

Example Lightlog data for Nov 30

The Colour Magenta

Colour WheelThe perception of colour is a really tricky topic once you start to look at it closely. While I was working on artwork for Light Log visualisations, trying to represent light data as a full colour spectrum, the more I started to notice that many illustrations of rainbows, spectrum and colour palettes seemed to have something unusual going on…

Of all the wonderful colours we experience, for most of us, our eyes only have colour sensitive cells that respond to three different areas of the electromagnetic spectrum. Blue peaks at 420 nano meters, green at 530 nano meters, and red at 560 nano meters. From these three colour cell types our brain interpolates all the other colours we perceive. Cyan for example is a pure wavelength of light in the electromagnetic spectrum, but our brain will also interpolate to cyan if our eyes collect a mix of both blue and green (on either side of cyan) wavelength light – if you’re looking at cyan on your screen just now, your brain is faking it out of blue and green pixels :) The most curious colour though is magenta, it’s purely a figment of our minds, no where to be found on the electromagnetic spectrum it exists only when our eyes see a mix of red and blue light. What’s strange is that the brain doesn’t interpolate between red and blue (which would be a green on the spectrum), but maps it to a totally new colour experience.

Who would have thought that the colour magenta only exists in our imaginations!

Visible Colour Spectrum