Describe the working principle of chlorophyll meter?

Answer 1

The meter measures how much of the light of a certain wavelength (best absorbed by the chlorophyll molecules) is absorbed by the sample.

The instrument measures transmission of red light at 650 nm, at which chlorophyll absorbs light, and transmission of infrared light at 940 nm, at which no absorption occurs (Hoel, Solhaug 1998).

Before the measurement, instrument is calibrated - transmission is measured with no leaf inside. Thus, when a leaf is clamped by the meter, a certain portion of red light is absorbed and the meter can calculate a relative value (in SPAD, from Soil Plant Analysis Development, units), showing how green the leaf is.

Basically, SPAD value correlates with actual chlorophyll content in the leaf, but measurements have to be taken at many points of the same leaf to be representative and calibration is to be performed for every plant species or cultivar to know the exact relationship between SPAD values and chlorophyll contents per unit area.

(i.e. after measuring chl. contents with the chlorophyll meter, pigments are to be extracted from the same leaf and its contents measured, for example, by spectrophotometry)

The meter measures how much of the light of a certain wavelength (best absorbed by the chlorophyll molecules) is absorbed by the sample.

The instrument measures transmission of red light at 650 nm, at which chlorophyll absorbs light, and transmission of infrared light at 940 nm, at which no absorption occurs (Hoel, Solhaug 1998).

Before the measurement, instrument is calibrated - transmission is measured with no leaf inside. Thus, when a leaf is clamped by the meter, a certain portion of red light is absorbed and the meter can calculate a relative value (in SPAD, from Soil Plant Analysis Development, units), showing how green the leaf is.

Basically, SPAD value correlates with actual chlorophyll content in the leaf, but measurements have to be taken at many points of the same leaf to be representative and calibration is to be performed for every plant species or cultivar to know the exact relationship between SPAD values and chlorophyll contents per unit area.

(i.e. after measuring chl. contents with the chlorophyll meter, pigments are to be extracted from the same leaf and its contents measured, for example, by spectrophotometry)