Hydrogen production by cultivation of cyanobacteria in photobioreactors offers a clean and renewable alternative to thermochemical or electrolytic hydrogen production technologies with the added advantage of CO2 mitigation. The objective of this study is to experimentally investigate the CO2 consumption, growth, and H2 production of the cyanobacteria Anabaena variabilis ATCC 29413-U under atmosphere containing argon and CO2. Parameters investigated are irradiance and initial CO2 mole fraction in the gas phase. The CO2 consumption half-time, defined as the time at which the CO2 concentration in the gas phase decreases to half of its initial value, appears to be an appropriate time scale for modeling cyanobacterial CO2 consumption, growth, and H2 production. The half-time depends on both the initial CO2 mole fraction and the irradiance. Also, two regimes of growth have been identified depending on irradiance. Below 5,000 lux, the irradiance and the initial CO2 mole fraction have a coupled effect on cyanobacterial growth. Above 5,000 lux, growth depends only on the initial CO2 mole fraction. Furthermore, the optimum initial CO2 mole fraction around 0.05 has been identified for maximum growth and CO2 consumption rates. The growth and CO2 consumption were not inhibited by irradiance up to about 16,000 lux. Finally, the proposed empirical models can be used in conjunction with mass transfer and light transfer models to design and optimize the operating conditions of a photobioreactor for maximum hydrogen production and/or CO2 consumption.