The problem of uneven current distribution across LED modules connected in parallel especially concerns luminaires with Safety Extra-Low Voltage (SELV), because the currents are higher and the voltages are lower. If the LED modules are consistently connected in series, each module is supplied with the same current and the problem described cannot occur.
Last but not least, it should be noted that a difference in brightness within a ready-manufactured luminaire can also be caused by other conditions such as incorrect module installation, inequalities or the contamination of reflectors and diffusers. Furthermore, other chemical impacts on the LEDs through the use of improper materials or caused by the environment, etc. are also possible.
Source 1: Luminous Flux and Current Uniformity Analysis in Linear LED Modules
Ming Lia, Keng Chena, Arnulf Ruppb, Daniel Chua & Divya Vangaria
a Osram Sylvania, Inc., Danvers, Massachusetts, USA
b OSRAM Licht AG, Garching, Germany
Published online: Nov 21, 2014.