Q: Why log light?
A: Light levels have a significant effect on our bodies circadian rhythm (our internal body clock that helps regulate biological processes over a 24-hour cycle). This has effects on our mood and energy levels. For those affected by Seasonal Affective Disorder, or the milder (but much more common) Winter Blues, light level changes in autumn and winter can have a noticeable impact on wellbeing. Being able to accurately measure your light exposure over time can help you manage its effects and make positive changes to your daily routine.

Q: How can I get involved?
A: If you have any questions or want to get in contact feel free to use blog comments, tweet to @lightlogproject, or email directly to gary@lightlogproject.org. If you’re in the Edinburgh area there will be opportunities for some hands on sessions making, using and experimenting with Lightlog prototypes. I’m making the Lightlog design as simple and open as possible to allow modifications and custom enclosures/jewellery. There should be plenty of opportunity for device personalisation. If you’re interested in software, data visualisation, or electronics, the project materials is being released under Open Software and Open Hardware licenses – it would be great to hear from you!

Q: How much does it cost?
A: There are no plans to commercialise Lightlog, but to give you an idea the current component cost is around £6-£10. There are a few additional sensors and components I’m considering, but I expect the final component cost to be around the £15 mark, a little more for a fully built version ready to wear.

Q: What is lux?
A: Lux is a standard unit of measurement for visible light. It can be used to measure how well or poorly lit our environments are. An overcast day can be around 1,000 lux; direct sunlight 32,000-130,000 lux; office lighting is usually 320-500 lux; home lighting 50-150 lux; a laptop LCD screen 20-300 lux. Seasonal Affective Disorder light treatment therapies are typically in the 2,500-10,000 lux range.

Q: What is colour temperature?
A: Colour temperature is used to describe a range of whites between yellow and blue. At the yellow end are things like the light from a match flame (1,700 K) or candle (1,850 K); at the blue end are the light from a clear blue sky (15,000-27,000 K), and the shadows in day light (7,500 K). Why is this useful to know? Bluer temperature light seems more effective at regulating the circadian system, though there is not enough research showing if it also makes a more effective Seasonal Affective Disorder light therapy.

Q: What data does a Lightlog store?
A: The prototypes uses red, green, blue, and clear light sensors (10-bits per colour) to continuously read multiple samples of light and store the average to memory. The sensors have a non-linear response from around 1 to over 100,000 lux, with most resolution between 50 to 50,000 lux. The client software is used to convert the raw sensor data to lux. There are also some simple meta data stored on the device for logging start time, time between samples, and number of samples recorded.

Q: How long can it record data for?
A: As long as the battery lasts :) but the longer you leave it between syncing with the app, the lower the time resolution of the data becomes. For example, if you leave it logging for 4 days, you will have roughly one record every 30 seconds; if you leave it for 4 weeks, you’ll have a record about every 3 minutes.

Q: How long does the battery last?
A: From testing prototypes so far the battery life is at least 4 months of continuous use. I’m hoping to continue to extend that as much as is practical. The battery used is a standard 3V coin cell costing less than 50p to replace.

Q: What licenses are used?
A: The circuit schematics and part list files are licensed under the Creative Commons Attribution Share-Alike license, which allows for both personal and commercial derivative works. The firmware and client software is available under the BSD 2-Clause License.

Q: So where can I find the latest source code and circuit schematics?
A: Source code, hardware schematics, and other documentation can be found on the Lightlog GitHub repository. Fork me, send me a patch! :)

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