Lux to par conversion?

Does anyone have a trick or a formula to calculate lux over to par, im looking to get some readings from my kessil LED pendants thanks in advance!!

 

You can't convert lux to par. Lux is weighted to the sensitivity of the human eye, using the photopic luminosity function. Once this is done, it can't be undone. Lux is a completely meaningless number as far as photosynthesis is comcerned. It tells you nothing as the curve is a bell curve centered around yellow-green. Our lights tend to be more blue, which is given no weight. So, you can have a tremendous amount of blue light and virtually no Lux. Or you can have a little yellow-green light and have a ton of lux, but absolutely no usable light.


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Hm so exactly how do i tell how much light im actually getting from these fixtures im pretty novice to the lighting aspects..

 

That's the problem. A lot of people think they can use a lux meter, but there really is no correlation between lux and par. Best to see if your local club has one of these http://premiumaquatics.com/aquatic-supplies/APG-MQ-200.html


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See this article for a conversion method.
Product Review: Lighting for Reef Aquaria: Tips on Taking Light Measurements — Advanced Aquarist's Online Magazine

I'm sure it is not the most accurate but I guess it's better than nothing. I would recommend you look into borrowing a PAR meter as m2434 suggested. Even a PAR meter is not perfect but it is the best method we have at the moment.

 

The conversion factors assume that the bulb produces the same spectrum that it did when they tested it. The problem is, that can be very sensitive to even slight differences in spectral output. This could be due to manufacturing, ballast, reflector etc... Also, probably most important age. Some bulbs will shift to yellow when older and get dimmer. Getting dimmer will cause both par and lux to decrease, however, shifting to yellow will not effect par, but will cause lux to increase! So, if your measuring a bulb with a lux meter, to see if it is still good, the shift to yellow will offset the decrease in output, with regards to the reading. So, it may look like the bulb is still good, but really it isn't even close.

 

Agreed 100% which is why I ranked the method as merely better than nothing.

 

i agree you can't convert Lux to par. It's two different things.