Beyond light output is also EMI/RFI from the electronics. I design LED drivers for a living and recently spent some time quietening an existing design I had which involved a bunch of test equipment (spectrum analyser and other 'bits).
Anyhow, I had a Rigid LED unit that was provided by one of my customers as a reference. I opened it up (of course) to see what Rigid had implemented to limit EMI/RFI and it looked like they had made a bit of an effort to provide some filtering at the power input, but on testing I was quite surprised (disappointed) to see that it still generated considerable noise. What I measured bore out in the real world testing my customer had performed - the noise would desense the FM receiver on the vehicle and weak signals would be wiped out.
The design I had implemented was considerably quieter (many dBm) and it was possible to wrap the power lead to the driver/LED assembly around the vehicle antenna without wiping out weak FM stations.
So, in summary, many folk care about how much light comes out, but there are other issues in a good product versus a cheap unit. EMI/RFI will wipe out your radio comms at longer distances (HF especially). Just something to consider when choosing a LED light. Cheap HIDs have even worse issues...
This is all above and beyond the quality of the LEDs that are used, the optics and the thermal path and thermal protection (driver electronics).
cheers,
george.
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