Using a Light Sensor to Measure Beetroot Solution Intensities

I found the qualitative results - just looking at the darkness of the solution and trying to decide which was darker - hard to draw conclusive results from, and began considering a quantitative analysis of the solutions. During my research, I found that many schools used a colorimeter to measure the results. A colorimeter is a device that measures the absorbance of different light wavelengths through a solution. I decided to try and make a crude colorimeter.

The basic idea behind my colorimeter was to shine a light through a solution, and use a light sensor to measure the total light absorbed by the solution. I used a LED at a fixed distance from the light sensor for the light source. To keep the light source constant, I excluded all ambient light by enclosing the LED and light sensor in a cardboard box, and held another piece of cardboard over the box opening when taking sensor readings.

To measure the amount of transmitted light, I used a light sensor connected to a microprocessor - an Arduino Eleven. The Arduino took a light reading every 0.5 seconds, and sent the results to the computer it was connected to. The sensor values ranged from 0 for total blackness to 1024 for dazzling light.

I placed a plastic tray above the sensor, so I could stand the jars between the LED and the light sensor. To keep the results consistent, I drew some marks on the plastic to help me place each jar in the same position every time.

When there was nothing in the ‘colorimeter’, the light sensor reading was 107. Each time I took a jar out of the colorimeter, I tweaked the LED or plastic tray until the reading (with nothing inside, and a piece of cardboard over the front) was 107 again. I believe this helped keep the results consistent. Also, each time I placed a new jar inside and the cardboard cover in front of the setup, I waited until the sensor readings stabilised and wrote that down as the sensor reading.

THE RESULTS

Placing a jar filled with pure water inside resulted in a sensor reading of 98, which I took to be a total light transmission reading. When I placed a jar with a lid on top, the sensor reading was 2, which I took to be a reading of absolutely no light transmission. As the pure water reading (what I considered total light transmission) was just under 100, and the reading for absolutely no light transmission was just over 0, I decided that the light sensor reading could be taken as approximate percentages of light transmission. This made the results a lot more meaningful.

Figure 1 - The general setup of the light sensor on my desk.

The light sensor

The Arduino microcontroller

LED

Figure 2 - A jar sitting on the plastic tray, between the LED and the light sensor.

Figure 3 - Placing a jar into the colorimeter.

The results I obtained looked quite similar to my qualitative results, but probably were more accurate:

Light sensor readings - from 0(no light transmission) to 100 (complete transmission)

Qualitative results - estimates of darkness on a scale of 1 to 7.

More Pictures:

Figure 5 - Another jar inside my homebrew setup to measure light transmission.

Figure 6 - What the data I obtained looked like.

Figure 7 - Holding a piece of cardboard in front of the box to block out ambient lighting that would bias the sensor readings.

Figure 4 - Writing down the sensor readings.