If you were in the middle of a tunnel and had to choose between going towards the lightened end and the dark end, what would you do?
Many organisms, such as animals and plants can sense light and are attracted to it. For example, you might have noticed that sunflowers turn towards the sun, during daytime, or that moths fly often near bright lanterns, at night. These organisms are called biological sensors.
Biological sensors are not the only elements that can sense light. You might have used once a lamp torch that charges with light and seen street lights turning on when it gets darks. These are examples of electronic sensors.
So which between biological and electronic sensors can best sense light?
Well, last week, with our bachelor interdisciplinary and scientific program, we developed projects in teams to compare biological and electronic light sensors. Our group decided to study Daphnia’s behaviour to light and compare it to the electronic LDR sensor, which is found in street lights, in some cameras and alarm clocks. So we tried to answer this question:
Which between the Daphnia and the LDR sensor is the most precise in distinguishing two lights of different intensities?
But what are exactly Daphnia?
Daphnia are small crustaceans (1 to 3 mm) that live in stagnant freshwater ponds. We learnt that Daphnia are attracted by light, which explains why they migrate to the surface during daytime or full moons at night.
Here is a link to an interesting article to understand how Daphnia sense light:
And here is a link to a video which shows Daphnia attracted by light:
And what is precisely an LDR sensor?
As was stated previously, the LDR sensor is quite a common and low cost light sensor. What does it do? It simply detects light intensities. When the LDR sensor is plugged to an electrical circuit and to a computer, we can then read light intensities values given from the LDR sensor on the computer. These values are low when the sensor is in presence of no or low light and they are high when the sensor detects high light.
To answer our big question above, we performed series of experiments with our biological and electronic sensor.
We first created a device (electrical circuit) with two LEDs and an LDR sensor. It allowed us to read on a computer and adjust the light intensity of each LED and to detect specific values of light intensities from the sensor.
We next installed our device in a dark room, and placed two LEDs on opposite sides of a clean lasagne dish, so we could play with the intensities of the two lights.
We could then observe the values given by the LDR sensor and Daphnia’s reaction to light by counting them on both sides of the dish, for different conditions:
- with both LEDs off (negative control - 1 on image below)
- with both LEDs on at their maximum (positive control - 2 on image below)
- with one LED turned off while the second LED intensity is regularly increased (positive control - 3 on image below). We did this same experiment for both LEDs
- with one LED turned at its maximum while the second LED intensity is regularly increased (Experiment - 4 on image below)
The results we expected for each of these conditions are presented also on the image below: the values given on both sides of the dish by the LDR sensor (in blue) and the distribution of Daphnia (in pink).
We tested this with 4 batches of around 100 Daphnia and with 4 different LDR sensors, to be sure of the validity of our tests.
Here is a simple graph showing the results of our controls: it shows in percentage, the difference between the light intensities values on both sides of the dish, sensed by the LDR (blue) and the difference between the number of Daphnia (red) on both sides also, in function of the intensity of one LED (one LED turned off while the second LED intensity is regularly increased).
As you can see, higher is the intensity of the LED concerned, the more the LDR can sense it. But Daphnia did not seem to react to this variation of intensity. We noticed in fact that they would prefer repeal bright light.
Because controls revealed the indifference of our Daphnia to light, we can not compare the sensors reactions with one LED turned at its maximum and the second LED regularly increased. So we cannot answer our big question above and make solid conclusions. But we learned that as Daphnia, LDR sensor have important variability and that LDRs seem less affected by external factors compared to Daphnia (temperature, day and night cycle, see http://onlinelibrary.wiley.com/doi/10.4319/lo.1975.20.4.0564/pdf...).
Hanaé BRADSHAW
Cécile CRAPART
Lucile SZPIRO
Fairouz GZARA
References:
- Cool Digital Photography, (2013). 31 Sunny Pictures of Sunflower. [online] Available at: http://cooldigital.photography/sunflower/ [Accessed 24 Jan. 2016].
- Bio390parasitology.blogspot.fr, (2012). Themes of Parasitology. [online] Available at: http://bio390parasitology.blogspot.fr/2012/03/normal-0-false-false-false.html [Accessed 24 Jan. 2016].
- Bbc.co.uk, (2016). BBC - Wonder Monkey: Like moths to a flame. [online] Available at: http://www.bbc.co.uk/blogs/wondermonkey/2011/05/like-moths-to-a-flame.shtml [Accessed 24 Jan. 2016].
- IFLScience, (2014). Why Are Bugs Attracted To light?. [online] Available at: http://www.iflscience.com/plants-and-animals/why-are-bugs-attracted-light [Accessed 24 Jan. 2016].
- HowStuffWorks, (2001). Why are moths attracted to light?. [online] Available at: http://animals.howstuffworks.com/insects/question675.htm [Accessed 24 Jan. 2016].
- Freepik, (2016). Freepik | Free Graphic resources for everyone. [online] Available at: http://www.freepik.com [Accessed 24 Jan. 2016].
- STEARNS, S. (1975). Light responses of Daphnia pulex. Limnol. Oceangr., 20(4), pp.564-570.
- Smith, K. and Macagno, E. (1990). UV photoreceptors in the compound eye of Daphnia magna (Crustacea, Branchiopoda). A fourth spectral class in single ommatidia. J Comp Physiol A, 166(5).
Thanks for sharing very helpful information. I found another LDR Sensor, site , they provide very helpful services.
ReplyDelete