Lux Meter readings

[DjGhostRider]

Can anyone help me understand these readings... I borrowed my buddies lux meter to see if I can figure out why my coral keep bleaching. I have the setting at 50% blue and 40% white. Checking with the meter, I'm showing approximately 100 at the top, 250 towards the middle and 350-400 at the sand bed. Does this make sense? Every chart I've read shows the numbers getting small as you go further down in the tank; why would mine increase?

 

[mcarroll]

Pic of the meter?

Also, you can also download a free lux meter to your smartphone.

-Matt

 

[DjGhostRider]

Thanks Matt, I just downloaded one.

This is what I was using.

 

[Reef Breeders]

I would suggest a par meter, as no one really speaks in terms of lux in this hobby. Lux is lumens/m^2, PAR is micro-mol of photons / m^-2 per seconds^-1, so the units are completely unrelated.

 

[mcarroll]

I would suggest a par meter, as no one really speaks in terms of lux in this hobby. Lux is lumens/m^2, PAR is micro-mol of photons / m^-2 per seconds^-1, so the units are completely unrelated.

PAR meters are so expensive - especially by comparison - I don't see how Joe (or Jolene) Reefer will be able to get that much more value out vs a lux meter. Of course, if value isn't a sensitive topic, then by all means...

That so few measure lux is unfortunate - it's cheap to measure and well understood. It's no less accurate than PAR (both require expensive non-hobbyist gear to measure accurately) and I argue just as useful. Of course that depends on your purposes, but ours are simple.

For example, nobody would have a problem discerning with a lux meter whether they were providing overcast, full sun or direct sun levels to their reef. Which is actually handy to know! Makes light acclimation much less of a mystery. Start under overcast skies (~1000 lux) with breaks of full sun (~10000 lux), eventually providing direct sun (>30,000 lux). And you can quantify the levels you are actually providing as you go!

Also, there is a relation between lux and PAR, but it's a different linear relationship for every light source you'd want to measure. "Lux ÷ Constant = µmol·m2·sec" There are lists of "conversion factors" out there for some known light sources. Mine wasn't, but yours might already have a conversion factor out there.

All the conversion factors for lights that are even vaguely like what we're going to be measuring (mostly 15kK-20kK reef lights) are pretty similar to one another. You'll only find wide discrepancy if you're trying to compare (e.g.) a pure actnic bulb to a warm white florescent. Unlikely comparisons, I think. This is why reading in lux in the first place is fine - the readings are inaccurate (no worse than PAR), but pretty consistently inaccurate. So still useful! A lot like our calcium test kits, for example, which aren't really accurate at all.

-Matt

 

[Reef Breeders]

I figured there would be some general comparison, but it simply deals in different units, which is hard to understand vs par. The only reason for that is that par is already used to measure light in the hobby by most, and lux is not commonly used to measure light output in reef tanks, from what I have seen. However, if there is a standard how much lux corals need, than it certainly can be used to measure light, and I believe that there was some info on that in the article you linked.

 

[DjGhostRider]

Thanks for the info you two. I'm just really having a hard time using LED's as compared to the MH/PC combo I have. With that it was simple, plug it in and set them on a timer. Now I'm having to adjust the intensity and everything just seems to be dying... I'm going to keep with it, but it's pretty frustrating.....

 

[mcarroll]

BTW, you meter isn't the same, but looks pretty darn similar to mine....I have no fancy case though. Not sure why yours would seem to be reading strangely like you described.

Some interesting info in the manual is that your meter is calibrated to a ~2800K light source. Gives you a better idea how to use those conversion factors if you want to get into PAR comparisons.

From the manual, I'd say our meters are the same in basic function. This meter is also not waterproof (at all) - how are you getting reading below the water surface? (BTW, readings at the water surface should be sufficient anyway. Below the surface is a math calculation based on depth, which in reality is randomized by all the ripples at the water surface. Shouldn't be too many needs to measure below the surface anyway.)

Let us know what the smartphone lux meter comes up with!

-Matt

 

[Reef Breeders]

Thanks for the info you two. I'm just really having a hard time using LED's as compared to the MH/PC combo I have. With that it was simple, plug it in and set them on a timer. Now I'm having to adjust the intensity and everything just seems to be dying... I'm going to keep with it, but it's pretty frustrating.....

What are your settings? How high is the light off of the water? If you have bleaching troubles, I would reccomend:

Turning down the intensity

Raising the light

and reducing the length of the light cycle to 8 hours

 

[DjGhostRider]

Right now I'm at 70b, 50w and the lights are 5-6in off the surface due to my canopy.

I'll try turning them down again and changing the cycle to 8 hours but I'll have to do modifications to the canopy to make it any higher.

 

[mcarroll]

Out of curiosity, have you taken any readings with your lux meter app?

-Matt

 

[Eienna]

Can't absorb the info right now, but I'm marking this thread. I wanna learn about lux and get the app to find out exactly where I stand

 

[DjGhostRider]

Not yet. And to answer your previous question, I just held the sensor up against the glass to get the previous reading as that's what my friend told me he did to get his reading. I've done some reading on converting LUX to PAR but that seems to be a bit much for what I'm looking for. I've also considered getting a PAR meter but I'm borderline because it may be too much of an expense for one time use. I'll sleep on it....

Out of curiosity, have you taken any readings with your lux meter app?

-Matt

 

[mcarroll]

Hold your smartphone or the sensor for the lux meter at the water line, facing straight up at your lights. i.e. The sensor will be "looking up" with a line of sight perpendicular to the water surface.

Mostly you're interested in finding your maximum lux reading and discovering how large an area of your water surface that maximum covers. So just glide your phones/sensor across the water surface until you find your hot spot (or spots, depending on your lighting) and then you're started!

You might also be interested in defining your so-called L80, L75 or L50 areas - or where light levels fall to 80, 75 or 50 percent below your measured maximum.

If you're curious about what light a particular coral is getting, just watch the shadow your phone/sensor throws on the rocks/coral below. You are sampling the light (more or less) that would normally be hitting that shaded spot (and the coral, or whatever is in it). Makes sense?

FWIW, light levels beneath the surface are highly variable under actual day-to-day conditions and is why I don't worry about trying to measure there. If you want to know the actual lux reaching a particular depth, just calculate it mathematically. It will be an "ideal" approximation, but that's all we're dealing with anyway - good enough.

Last, I really wouldn't worry about converting to PAR for your own needs. You'll be fine dialing in to the natural target ranges of "overcast", "full sun" and "direct sun" and gauging with your lux meter. (If you needed to compare with someone else's PAR readings conversion may be worth it, but that's not really the case here.)

-Matt

P.S. There're only about 4 hours or so of peak light levels in the tropics. If you have the lights up to direct sunlight levels (per the lux meter) keep this "time limit" in mind and make sure the ramp-up and ramp-down periods are pretty dim.

 

[Eienna]

That sounds hazardous to your phone

 

[mcarroll]

Well, maybe it would be a good idea not to take lux readings immediately after eating popcorn! (Butter fingers!) Maybe try putting the phone in a ziplock bag and see if it throws your readings off much? It could safely take a quick, accidental dunk if sealed in a ziplock.

On the other hand, if you just can't resist the buttery crunch of some popcorn while taking lux readings, then perhaps a very inexpensive (practically disposable @ about $15-$20) handheld meter is right for you!

:xd:

-Matt

 

[Eienna]

Lol!!
Worth a shot...

 

[miamiangler]

I
have the Seneye Reef which I bought from Rick at Reef Radiance . It works for me and seems to work well . It Takes PAR readings and Gives Lux readings also . I am happy with the unit . I have my lights set at 25 % whites and 40% blues .My top readings are at 380 and middle reading is at 230 in my 29gal reef tank . so far all fish and corals are happy.

 

[Greenstreet.1]

I
have the Seneye Reef which I bought from Rick at Reef Radiance . It works for me and seems to work well . It Takes PAR readings and Gives Lux readings also . I am happy with the unit . I have my lights set at 25 % whites and 40% blues .My top readings are at 380 and middle reading is at 230 in my 29gal reef tank . so far all fish and corals are happy.

Happy new year to all. ? Since you get both readings is there any way you can tell us what 380 and 230 par would equal in lux just downloaded one of the apps

 

[miamiangler]

This are the readings I just took with my Meter . All meters Might read a little different . I use mine just to make sure some corals don't get to much light . I get different readings in different parts of the tank ! This is dead center Top Par381 lux 14366 center front middle Par281 lux 10372 . Hope this helps . ALL FISH EMPORIUM (LFS) has a Par meter for 129 dollars ..