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[Kyle Malenfant]

Hey I have two questions regarding lumen output and photometric data.

1) How much more additional lumens (difference) is necessary in order to see a substantial increase in output?  For example, at 2M with the same beam angle and color (red, green, or blue for example) if one fixture is measured at 2,000 lux, what should a fixture with noticeable greater output be rated at?  2,500?  3,000?  I suppose I'm trying to understand at what incremental difference is it worth spending extra money.

2) I often find discrepancies in the photometric data provided by the manufacturer when compared to manual calculations using the inverse square law.  So which do I follow?  My calculations using the formula or the printed data?  The numbers are not off by much, maybe 5-10% difference.  Just curious what others do.

Thanks!

[James Feenstra]

1) it depends on what's looking at the light...if it's a camera, a few lux can make a considerable difference, if it's the human eye, it really depends on a lot of things as our eyes adjust to the environment around us. That being said, 500lux between fixtures will definitely be noticeable

2) manufactures specs always appear better than the fixture really performs, simply because they're the best generated results in a lab test....same as audio specs!

[Nicolas Poisson]

2) manufactures specs always appear better than the fixture really performs, simply because they're the best generated results in a lab test....same as audio specs!

True but the inverse square law is not acurate as well. Like for audio, it is applicable to a spherical model, which can differ from the real directivity.
I compared once the photometric data provided by American DJ on their Flat Par to measurements I made, and this matched.

[Kyle Malenfant]

All great points.  Thanks

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