LUX vs PAR?

[GeorgeMonnatJr]

Is LUX degradation proportional to PAR degradation? That should be the question to know if you can use a lux meter to check the life of your bulbs.

The answer is really, "Maybe." Lux, or luminous flux, is a measure of how well the human eye would respond to the light. The human eye is vastly more responsive to green light.

So really lux is a measure of how "green" a light is. If your bulbs degrade all wavelengths evenly, then yes, a lux meter is a great way to measure degradation. If your bulb doesn't degrade at all in the green, or degrades less in the green than in the other "colors", or if it shifts from another wavelength to green, then it's a horrible relative measure.

PAR is an equal counting of all visible light photons. That's why it's a better measurement of aquarium lights, especially if corals don't care about green but cyano/dino/bryopsis/etc. love green light.

By the way, lux and the human eye response is why a green LED will look super bright to you while a blue or royal blue will look dim. But the blue is probably giving off a lot more energy than the green, which may cause some people to bleach their stuff as they turn up the blue LEDs to make things look as bright as their old MH.

 

[alton]

When I checked my tank using a foot candle meter and a PAR meter it was. The difference across all three Radium lamps where proportional.

 

[GeorgeMonnatJr]

When I checked my tank using a foot candle meter and a PAR meter it was. The difference across all three Radium lamps where proportional.

In a lot of cases it may be exactly the same. A lot of detectors, including Apogee's quantum sensor, are based on silicon which all have response curves similar to the green one in the previous picture. So if your LUX or PAR sensor isn't calibrated for different wavelengths or weighted differently, it would read just like the green line. Or you have very green light

 

[alton]

I ran into an issue with a marineland reef capable led fixture. I checked each of the leds with a foot acndle meter, the best had 3500 ftc, the worst only had 700 ftc. I could not tell the difference between the ones from 1600 to 3500, they looked the same. Only when the leds got below 1000 ftc could you tell they where not as bright(the human eye can not tell). I found this out the hard way the first time I switched to MH, after 8 months my corals started to die and I could not figure it out? Finally got to the the lighting and it had dropped by 50% and in only 8 months. I switched to Reeflux and now Radium and never had that issue again.