LUX meter results

[coraldaddy]

While playing with my new meter I found the following results. Please post your results, especially with the LED lights. Curious to see what kind of readings people are getting.

MH - 12" away (not submerged)
20K Radium on electronic ballast 18,000
14K Pheonix on electronic ballast 26,000

Halogen 55W -12" away 120,000

P.C. 32W dual - 3" away 16,000
LED flashlight - 3" away 17,000 (9x1W LED) very narrow field

I am trying to find a Lexon LED flashlight to get a reading of that bulb, so if anyone has one please post your readings.

I rounded the numbers off. I also measured N.S. @ about 8am on clear day at 108,000.

Thanks

 

[hahnmeister]

Most of the light readings you will see here are with PAR meters, not Lux meters. It makes it pretty hard to compare.

 

[o.c.d.]

PAR=1.53+(0.0111)Lux
multiply Lux reading by 0.0111 and add 1.53 to get PAR value

 

[hahnmeister]

That is not correct. That equasion assumes a certain Spectrum. The photometric and radiomatric scales measure different colors in different ways. The photometric scale, for instance, doesnt measure blue with accuracy because WE dont see blue with accuracy (only 10% of our cones are tuned to pick up blue, while about 50% are tuned to see red). The photometric scale is based on what WE SEE, not how much actual light there is. So there is no conversion from PAR to Lux... at least not easy.

You CAN convert if you know the exact amounts of each frequency (color) of light being measured... but if you had an instrument to do that (a radiospectrometer... $1000-2000 on up) you wouldnt need to convert PAR and Lux, would you?

And so converting Lux to PAR becomes an integral of the spectrum across 400-700nm. So for example, while a 400 watt 10,000K bulb may give a PAR reading of 200 at a given distance/point from the bulb, it may have a lux reading of 1000 at that point. But if we switch the bulb to a 20,000K, its PAR may be 150, yet its lux may drop not by 25% to 750, but to 500 or less because the blue spectrums wont show up. In this manner, measuring bulbs in the Lux/photometric scale as say, a bulb degrades and color shifts may give you the same lumens/lux because less blue may be made, but more warmer spectrums from shifting will cover it up. Yet overall, the PAR, or REAL light output of the bulb will be going down.

The only reason that conversion formulas like this:
http://www.madsci.org/posts/archives/2000-08/965136947.Ph.r.html
... are correct is because they assume a fixed spectrum.

I forget the exact formula for integration, I know Sanjay knows it. But its rather useless without knowing the spectrum anyways.

 

[o.c.d.]

So when I read that the equation is 95% accurate thats BS.Someone should tell J.C.Delbeek and J.Sprung because thats what they wrote pg.458 The Reef Aquarium Vol.3.Apparently they didn't do their homework?

 

[hahnmeister]

Ill get back to you on that one. Rather than try to figure it out, Ill ask Dana Riddle since its 'his guy' Delbeek that said it. The accuracy Im sure varies depending on the color temp of the bulbs being measured. A more monochromatic blue source, for instance, like a blue LED or even a pheonix/radium halide bulb, I think is going to be outside that 95% accuracy.