Precise control of a correlated color temperature tunable luminaire for a suitable luminous environment

Correlated color temperature (CCT) affecting emotional feelings should be adequately adjusted according to the change of atmosphere. To control CCT, luminaires use a specific method, which combines higher CCT of the lamps and the lower ones. However, when two different CCT lamps are combined, the realization of target CCT using a simple proportional equation is not appropriate. Therefore, this study assessed three different methods to calculate appropriate combination ratio for two different CCT light emitting diode (LED) lamps, and then measurements were conducted with calculated values from such methods in order to find the precise control of CCT. The first method is to calculate the combination ratio by using a simple proportional equation. The second method is to calculate the combination ratio by considering a change of the characteristics of light according to dimming. Lastly, third method is to calculate the combination ratio by using the McCamy's Equation along with a change of tristimulus values according to dimming lamps. The most appropriate method has been identified by comparison between target CCT and measured CCT values. This study also evaluated how the calculated CCT values were measured in an architectural space. As a result, the third method is the most appropriate one, and proven to be used in the architectural space. The third calculation method based on CCT tunable lighting system will lead to more suitable luminous environment and then enhance visual and emotional aspects of occupants in a luminous environment.

► We suggest precise method to calculate combination ratio for realization of target CCT with two different CCT LEDs.
► We examine changes of CCT and tristimulus in accordance with dimming.
► We propose three different methods.
► We assess three methods by comparing measured values with target values.
► We evaluate whether the third method is valid in the architectural space with CCT tunable LED luminaires.