Technical Abstract: Despite a century of research, we still lack a concrete, mechanistic understanding of solar radiation and temperature effects on anthocyanin accumulation and composition, crucial for red wine grapes. Our aim was to elucidate the mechanistic response to microclimate of anthocyanin metabolism in Vitis vinifera cv. Merlot, in this case solar radiation. This study was unique in that temperature, radiation intensity, and relative humidity were measured continuously for the duration of treatment. Treated clusters included 1) control-shaded (CS; ambient temperature); 2) control-exposed (CE); 3) light-excluded (LE); and 4) aspirated light-excluded (ALE). Aspiration was initiated and terminated dynamically in reference to the temperature of CS clusters. For treatments LE and ALE, randomly selected healthy clusters were shaded at the onset of véraison (one to two berries turning color) by polypropylene enclosures comprised of a white exterior and a flat black interior. All experimental clusters were located on the west aspect of the canopy. Treatments were imposed until a composite berry sample from untreated clusters reached commercial ripeness (~23 ºBrix). Harvested grapes were chemically extracted and extracts were analyzed for individual anthocyanins by HPLC/DAD. All of the 15 anthocyanins reported in ‘Merlot’ grapes accrued in all clusters, indicating that no individual accumulations were terminated by light exclusion during ripening. Overall, both LE and ALE clusters accumulated less total anthocyanin (86.8 mg of malvidin-3-glucoside/100g berry) than the controls (160.2 mg of malvidin-3-glucoside/100g berry). Proportions of individual anthocyanins were altered by light exclusion. The ALE clusters had the least total anthocyanins (75.4 mg of malvidin-3-glucoside/100g berry), but higher percent acylation (52% of total anthocyanins) than other treatments (CS-36%, CE-37%, and LE-42%). This work contributes towards our growing body of knowledge on environmental stresses and anthocyanin development in grape berries.