Q.T.W. Engelmann's classic experiment, which split light through a prism across a filamentous green alga (Cladophora) in a suspension of aerobic bacteria, showed that the bacteria clustered most densely in the blue and red regions of the spectrum. This established that:

The modern understanding of photosynthesis was built up through a sequence of classic experiments spanning nearly two centuries. Priestley (1770s) first showed a green plant restores something to sealed air that a burning candle or living mouse had used up. Ingenhousz refined this, showing the effect requires both sunlight and the plant's green parts specifically. Sachs (1860s) demonstrated that illuminated leaf tissue accumulates starch (tested with iodine) specifically within chloroplasts, localising CO2 fixation to that organelle. Engelmann (1882) split light through a prism across a filamentous alga in a suspension of aerobic bacteria, showing the bacteria clustered densest in the blue and red regions -- establishing that the action spectrum of photosynthesis parallels chlorophyll's absorption spectrum. Blackman (1905) showed photosynthesis must comprise at least two mechanistically distinct phases, based on differing light- and temperat …