I am reviewing LED light fittings for an industrial premises refit. As with most of the experienced users on this site I like to understand what I'm purchasing and have opened up a sample fitting to have a look. To my surprise I find that the LEDs are arranged on three PCBs as shown in Figure 1.

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Figure 1. LED light fitting comprising of three PCBs in parallel connection, with 12 series connected rows of 6 parallel LEDs on each board.

The array is driven by a constant current power supply which looks OK but I've never seen an array of LEDs driven like this and here on EE.SE we advise people all the time not to do this.

The distributor is giving a 50,000 hour warranty on the lamps (which is good). He also says that if a chip dies the "circuit will compensate" which I take to mean that the others in the row will have to pass more current. The build quality looks good with a much larger PCB than other brands with most of the copper left on the board which should help with heat dissipation.

Can anyone comment on the likely reliability of this arrangement and how, if one were manufacturing this fitting, if LED selection and matching would be carried out?

  • 2
    \$\begingroup\$ I work at a major North American lighting manufacturer and, although I'm in the 'Networked Controls' division and not 'Luminaires', I can confirm that this is a standard arrangement. Anecdotally I've heard that the LEDs themselves are sufficiently well matched in each batch that 'paralleling' them together like that does work, and that the fixture is also usually given a current rating such that each individual LED is running well below its maximum operating current - allowing for the odd failure to not overstress the others... \$\endgroup\$ – brhans May 24 '16 at 15:22
  • \$\begingroup\$ Its also likely that when buying LEDs in such volume we can specify how closely matched the LEDs in a batch must be - but that's really just a guess. \$\endgroup\$ – brhans May 24 '16 at 15:23
  • \$\begingroup\$ Thanks for the comments on this, chaps. That sets my mind more at ease. \$\endgroup\$ – Transistor May 27 '16 at 21:10

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