Melvin Calvin at Berkeley in 1945 showed that Chlorella could take up ¹⁴CO₂ and produce 3-phosphoglycerate. 
 This article is for wider audience interested to know that carbon fixation cycle  is not “Dark reaction”  or  ” Light independent carbon fixation cycle” but is "Light dependent Carbon fixation".


Calvin cycle enzymes are present in mesophyll cells of C₃ plants but they are absent from mesophyll cells of C₄ plant.
 In C4 plants the RuBISCo is present and active in Bundle sheath cells only where they fix CO₂ during day time. 

In CAM plants the  initial fixation of Carbon di oxide takes place in cytoplasm of mesophyll cells via activity of PEP carboxylase during night as they have to economize on water and as  their stomata are closed during day time and open during night only. However CAM plants also transport back their Malate initially produced as fixation product using 3 carbon acceptor PEP and enzyme PEPcarboxylase.

 Irrespective of the location the C₃ fixation takes place in C₄ plants as well as CAM plants and basic process is same in all the three. 

Its spatial separation of enzymes in C₄ plants and its temporal separation of reactions taking place in the same cell. 

Long time ago we published papers on role of PEPcase in light fixation in C3 as well as C4 callus cultures of Carrot, Peanut ( C3) Maize (C4) along with RuBisco.  (Neumann, Kumar and Imani 2009).

Ribulose bis phosphate carboxylase oxygenase (Rubisco) : 
 
 Probably the world's most abundant protein Rubisco makes around  50 percent of all the plant proteins but its activation is regulated by several factors and light is one of the important factor which activated the enzyme and electron transport chain regulates activity of several enzymes of Calvin cycle involved in process of regeneration of acceptor molecules. Ribulose-1,5-bisphosphate is the CO₂ acceptor in CO₂ Fixation. Fixation is accomplished by ribulose bisphosphate carboxylase (oxygenase) = RUBISCO.  

Here are some of silent featured of Carbon fixation:  
 1. Calvin cycle takes place in stroma region of Chloroplast. 
2. The shift in pH in the stroma region is induced by light induced photolysis of water and electron transport chain which results in acidification of lumen inside the granum and accumulation of H+        in  lumen of the grana results in lowering of pH inside the granum but at the same time increases pH in the stroma (pH 7.4-8.0) just outside the grana.
3. The pH range of 7.4 to 7.8 is ideal for activity of RuBisco. 

 Some of the important steps needing light for activity of Calvin cycle include. 
 a. Light induced change in pH of stroma region to activate RuBisco. 
 b. Rubisco is activated when carbamylated (CO2 added to Lys201) and with Mg++ bound. • RuBP (substrate!) is inhibitor which binds with RuBisco in dark and must be released from inactive Rubisco by Rubisco activase. Carbamylation and Mg then activate. The activities of key Calvin cycle enzymes are coordinated with the output of photosynthesis and, these enzymes respond indirectly to light activation. Rubisco activation requires: Light, CO₂, Mg⁺⁺, and pH ≥ 7.4 Light induces movement of Mg²⁺ ions from the thylakoid vesicles into the stroma.

c.  Light energy generates reducing power:Reduced ferredoxin and NADPH.
d.  In presence of light, electron flow through PSII, Cyt b6f and PSI cause protons to be pumped into the lumen. The resulting charge gradient drives the Mg++/Cl- antiport and Mg++ moves into the stroma. 

e. Electron flow through PSII, Cyt b6f and PSI also produces reduced ferredoxin and e- flow through ferredoxin-thioredoxin reductase yields reduced thioredoxin which is an activator of several Calvin cycle enzymes (-S-S- to –SH HS-). 

f.  Light-generated reducing power (Fdred = reduced ferredoxin) provides e- for reduction of thioredoxin (T) by ferredoxin-thioredoxin reductase (FTR). 

g. Thioredoxin activated enzymes include ribulose-5-P kinase, sedoheptulose-1,7-bisphosphatase, glyceraldehyde-3-P dehydrogenase and Rubisco. 

This is enough indication that Calvin cycle is not a dark reaction and is also not Light Independent reaction but it is Light dependent carbon fixation which takes place during same time as  the Light reaction.