Step 6Let's measure!

Working in the dark

Because the LDR reacts to light, you'll have to make sure to work in as dark an environment as possible to prevent any stray light from hitting the detector.
You could put the whole device in a dark box, or darken the room you're working in.


Blank measurements

Since the LDR reacts differently to different wavelengths of light, we need to make blank measurements before we can go any further.
To do this, fill the cuvette with distilled water (or any other solvent you plan to use) and note the voltage reading for each wavelength or light color you pass through the cuvette.


Real measurements

After the blanks have been measured, fill the cuvette with the solution you want to measure. Then, for each wavelength or light color, note the voltage reading. Be sure to use the same light color as you did during the blank measurements. (i.e. make sure that the CD is in the same angle and / or that the color of the light passing through the cuvette is the same as during the blank measurements)

Now you can calculate the absorbance, according to the Lambert-Beer law. A = log (I0 / I) where I0 is the intensity of the light falling into the cuvette (i.e. the blank) and I is the light passing through the sample.

(the attentive reader will notice that the multimeter always reads 8.16 on the pictures; this is because the photographs were taken in daylight rather than a pitch black room)