# What do light meters measure ?



## Flear (Oct 5, 2012)

What do light meters measure ?

everything i find says "it measures light", ... but blue is different from green, different from yellow, different from orange, different from red, different from ... and so on.

visible light, accepted as 400-700nm is a range of energy frequencies.

light meters, the little i am familiar with, (without owning one as i consider it waste of money to buy something that fills me with false confidence till i know what they are measuring.)

light meters measure "light" photons, from 400nm to 700nm and give an output reading of X, ...output readings could be 10, could be 24, could be 78, ... to say there is X amount of light 

is it measuring an average ? (could provide spikes and valleys and still give a high average)
is it measuring specific wavelengths ? (could peak these wavelengths and low-ball everything else)

i would think every nm wavelength to be excessive, don't really care to know how much 400nm & 401nm & 402nm, ... but could measure ranges of 10, or 20, or 30, or whatever to give a good estimate of what various lights are giving out.

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so i wonder, ...what are light meters measuring ?


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## Mikaila31 (Dec 18, 2008)

most common measurements are lux, lumens, and par. par being the most applicable to this hobby. some of the higher end bulb brands will give a spectrum graph for their bulbs, which is the nm measurements.
_Posted via Mobile Device_


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## Flear (Oct 5, 2012)

yup, i'm familiar with the spectrum measure lights are (hopefully) sold with.

for plants, i'm familiar with the photosynthesis preferences on that spectrum as well.
(at least it's shape)

i just have a hard time listening to a meter that would convert all that into a single number


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## Agent13 (Apr 23, 2013)

The nanometers correspond to colors of visible light. However a UVA/B light meter will detect light outside out visible range . Closer to 700 the closer to red. The closer to 400 the closer you are to ultraviolet and blue. The numbers are a direct correlation to color . 

And ... They do work. I have to keep track of invisible light output for my reptiles . My eyes could never tell me if that is degrading since visible light can still be bright while their usable light is diminished. I've had a dragon that appeared sick. Was darkened in color and lethargic . A light test showed the bulb wasn't producing sufficient light .. Changed the light and the dragon was better within the day . 


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## Flear (Oct 5, 2012)

agent13, ... but is that all the light meter is good for ?, ... to give a general yes/no there is or is not sufficent light ?

i trust your experience, ... but i'm still kinda skeptical.

i would like to know what the light is failing to meet, if it can be met by the addition of a more specific light, or if it's time to replace the bulb. is it following a healthy photosynthesis "M" or just a couple peaks and leveling out everywhere else ?


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## Agent13 (Apr 23, 2013)

The numbers are what you're supposed to translate . They don't make one that I'm aware of that simplifies the results for you. You'll find it easier to use once you have one for a while . You can set a baseline if what you expect to see that way. It's not an investment you make without understanding research . The better ones are $180 plus so it's hard to say it's worth it. When you have animals health depending on it saving you vet bills it's a little easier to justify . When running planted fish tanks it can be fun to use and know what's going on there but financially I have to admit I don't think it's worth it ... Not if $ is a concern . 


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## Flear (Oct 5, 2012)

so don't care about the output wavelengths as they degrade over time, ... change bulbs on a regular basis (6mo or so) get bulbs that are rated to have a desired spectrum output.

till important critters health is on the line, then consider the investment of a quality meter, ... k

i guess then, can't beat the simplicity


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## Mikaila31 (Dec 18, 2008)

Well fish wise, our fish are not dependent on light. For a non-planted tank light isn't actually needed beyond ambient room lighting. For planted tanks tho PAR is the main measurement for light useability. Everything else is preference really... like color temps, I prefer a higher one then most. We don't care much about UV spectrum unless its aquatic reptiles. I personally do not replace my bulbs regularly, even for my planted tanks. Last one I bothered to replace was a couple years old and broke in half in the fixture which is why I replaced it lol. Doesn't matter if they are $13 power compact bulbs or $2 spiral CFLs they usually run for a couple years. And yes there is some degradation, but its typically to a point or tapers off eventually. Even the high output LEDs have degradation and no one worries about those. 

A proper PAR meter is costly, but they are informative since light is strongly effected by water in some ways. But the effect of light in water is fairly predictable, as much of this hobby is. Most wavelenghts do not penetrate water very well, even over the depth of our tanks. Its why plants typically grow in shallow waters despite clarity. You get deep enough all that is left is the blue light spectrum.


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## Agent13 (Apr 23, 2013)

I know UV isn't needed for fish ... Yet the numbers are still able to translate colors in your spectrum . You just have to know what number means what .. That's not hard. While the reds are good for plants we know those are filtered out very early . That would be on the 600-700nm end . The blues that make it deeper are in the 300-400 end . 
Par Meters are great .. They too measure a lot of the same things though . It's all useful info if you happen to already have one . If you want optimal growth for your t8 or t5 or t5HO or such .. Then you'll want to replace every 6-9months but it's not at all critical . The difference is only noticeable if you're really anal about that stuff . The LEDs are same .. They degrade yet the reason why people don't talk about that is because they take MUCH longer to degrade then fluorescent . So much longer that it's not worth the worry . 


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## Mikaila31 (Dec 18, 2008)

LEDs do last longer and are usually much better than CFLs at lifespan, but there are many variables that effect any bulbs performance. Its part of why I prefer to build my own hoods as bulbs will usually preform better for longer in comparison to the overpriced store fixtures. Manufacturers usually are not interested in efficiency as much as they in making a fixture compact and sleek looking. Poor ventilation, higher temps gives higher degradation of the bulb. A super compact LED fixture can have just as bad degradation as a T5 fixture. Like I said this degradation tapers off for both bulbs. The heat is important too, as the high output LEDs get hot and the hotter they get the faster they will degrade. Poorly or minimally heat sinked LEDs will not preform as well. T5 HO will degrade faster then a regular T5. T5s have also improved greatly in getting lower degradation and longer lifespans in recent years. You are basically looking at lumen maintenance. Other factors that effect this are frequency of starts(those that do a 'siesta' hour for a planted tank will degrade bulbs faster) and how the bulb is driven. Under driving LEDs will reduce degradation but at loss of potential output too. Don't use magnetic(flickery) ballasts for florescent bulbs as they degrade and decrease lifespan significantly. The light should be instant on always. A lot of the standard aquarium strip lights still use the old outdated magnetic starter ballast to light them. Which is a bit sad considering how much they sell those fixtures for. There are a few long life T5 HO bulbs out there and they do not cost much more and most have low degradation, rated to 45-60K hours.

L.E.D. Rite, LLC - Performance Data

A properly designed LED fixture with GOOD LEDs(like CREE or similar) will certainly out preform good HO T5 fixture. Its just a lot of manufactured fixtures in this hobby are not properly designed for this, that goes for all types of fixtures. I would rather spend more to build my own fixture that preforms efficiently and is bulky in comparison then to buy some of the common cheap fixtures like the odyssea stuff.


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## Agent13 (Apr 23, 2013)

Ah yes .. Very good point Mikaila . I suppose when I speak about lights I really do simplify greatly . The ballast is highly important for performance. As is the build of the LED. T5hO is better then t5 if you do get one of the better newer bulbs .. But then again I'm a lighting nerd by necessity from my reptile endeavors . 
I'm absolutely guilty of wording things confusingly in a simplified manor .. But I guess I was hoping how I explain things would start the ball rolling for those who perhaps wanted to further research . 


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## Flear (Oct 5, 2012)

(yes, i've lost composure & focus in my post here)

all i can say is i know the basics.
when it comes to the detailed bio-chemistry it's all above my head currently
when it came to considering lighting intensity over the course of the bulb, information is hard to come by

i know heat is a big killer for bulb life.

as agent13 has explained the life of a bulb and what that does to it's intensity/spectrum output ... things start to degrade rather quickly when rated life of these lights try to claim 20,000 or 50,000 hours (so you won't stub your toe in the dark for those 20-50,000 hours (depending on light technology) but they won't be of any other use than that at the end of the rated life.

from previous searches, i could find 'rated life' and eventually found 'economic life' (that's a messed up definition)
rated life being the expected # of hours that 50% of the lights will still function (when used for 10 hours a day - as opposed to on & off all day)
and economic life, something about bulbs at 80% of the rated life

as Agent13 mentions, changing every 6-9mo. ... that's about 95% of a bulbs rated life remaining when considering fluorescent lights.

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at the time i did that search i came across induction lights, ... about as expensive as LED lights to setup it looks like. unfortunately producers are busy marking these to cities for street lighting (which clearly has a better spectrum over HID lighting, ... a spectrum customizable with the same range and technology as fluorescent lighting (phosphor mix)

rated life for these are about 2x LED. 

when it comes to replacing induction lights, ... for the more intense bulbs (say 400watts) they're about as costly to replace as the equivalent # of fluorescent bulbs - but still, say near $200 for a bulb in that wattage

induction lights do run much cooler though than any other light out there, perhaps that's where it's rated life is so good. ... from the few numbers i have seen, they are somewhat more efficient than LED (lumens per watt)


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## Mikaila31 (Dec 18, 2008)

I've never really paid attention to life span rating, because I know how variable it is. I can tell your right now I do not have a single bulb running that isn't beyond its supposed 'economic value' I currently have ~15 fluorescent bulbs running just for tanks and it has been that way for the last year or more, running 8 hours a day. I've replaced at most 3 bulbs in the last year do to burnouts and one of those was with a previously used bulb. I typically expect 1-2 years from bulbs when I use them, but thats just me. Going by that 80% of my bulbs far exceed their life expectancy especially since a lot of them are 'rated' for 10,000 hours. These are my planted tank, even my CO2 injected ones. I am well aware of the output loss but disagree on how much it happens. I grow plants and they grow well. 

Sorry flear but not everything is equal. There are lots of poor cheap bulbs out there but they are nothing compared to the chinese LEDs that flood this hobby. There are good preforming bulbs out there, same for LEDs. 
http://www.usa.lighting.philips.com/pwc_li/us_en/connect/tools_literature/downloads/p-5752.pdf
http://assets.sylvania.com/assets/D...89) .d8e0bd0a-4151-451c-ac79-1428e8d74883.pdf

In the end it depends what you want. I've stuck with power compact bulbs for years instead of HO T5 simply because I really loved GE's Aquaray bulbs and that was about the only option for them. Now the 55 watt version was discontinued and currently the three 1-2 year old bulbs I have running are the last ones I have. I ordered the endcaps I need to switch that fixture to HO T5 at some point. I'm still bulb hunting for what I want for HO T5s. Its easy enough to get cheap 6500K T5s but thats lower then what I prefer. I run 6500K on most my other tanks, simply for cost/preference balance. Either I'm stuck with running 6500K or mixing 6500K and 10000K. And there isn't much out there for generic 10000K T5s apart from coralife and soon as coralife puts there name on something it costs 80-100% more =/

Usually it comes down to balancing cost and preference. Thats why I use a lot of cheap 6500K 13 watt spiral compacts. It simplifies things in my world anyway. Its certainly not the best lighting, but it does what is needed very well.


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## Flear (Oct 5, 2012)

the CFL spiral bulbs i'm going to settle on for growing greenwater (and put the bulbs directly in the water).

otherwise i consider these bulbs to be inefficient as over half the bulb is facing itself. (so i stick with linear lights)


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## pop (Aug 29, 2012)

Hello Folks;
I have one small insignificant question is plant available radiation measurement identical to plant useable radiation? Will light measurement instruments provide PUR readings? Do light meters identify PAR Attenuation as well as PUR attenuation?
pop


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## Mikaila31 (Dec 18, 2008)

Flear said:


> the CFL spiral bulbs i'm going to settle on for growing greenwater (and put the bulbs directly in the water).
> 
> otherwise i consider these bulbs to be inefficient as over half the bulb is facing itself. (so i stick with linear lights)


You do realize how dangerous putting a CFL directly in the water is right....? These typically are not waterproof and they run on high voltage low amperage. If you are talking about the standard household ones they are gonna short out on you really fast. 

I am aware of their restrike cons, but vast majority of manufactured linear fixtures also are not designed well to minimize restrike. I grow a whole lotta plants with my army of spiral CFLs. They are also self-ballasted so it simplifies the fixture. You can replace ballasts without too much difficulty on linear fixtures but they are not cheap. At best you have a well designed fixture that doesn't cook a good quality ballast, but thats sadly not typical of most manufacturers. Everything has pros and cons and that includes linear fixtures as much as the spiral CFLs


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## Flear (Oct 5, 2012)

Pop, aside from there is PAR & PUR, ... i couldn't tell you what the difference is, i remember seeing a picture on a google image search, that shows, ... but i can't say more 

Mikaila, oh, i'm aware i don't want to submerge the whole thing, just the spiral part, and with a guard to keep the water off the ballast side so it doesn't short out.


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## Mikaila31 (Dec 18, 2008)

PAR is photosynthetically active radiation. It is the measure of light in the spectrum that is suitable for chlorophyll to use towards photosynthesis.

PUR is photoshynethetically usable radiation. PUR is more of an exact measurement of how much light of PAR is in what spectrum. The issue with PUR is that is will be different amongst different species of plants. A green crypt. has different chlorophyll and thus different absorbance than say a bronze crypt. The PUR would be different then for each plant species. This also makes PUR very difficult to calculate... it is estimated at best. Basically plants prefer red and blue light, however any plant with red coloration will be reflecting some of that red light and will be more dependent on the blue spectrum and probably yellow then a typical green plant. 

Flear I still say that is a very bad idea. They are not meant to be submerged even partly, that 'encased' ballast has little protection. The wires that feed current into the bulb are in place when the glass bulb is sealed shut. They are fixed in the glass, at best they put little loose sleeves over these bare wires to avoid them shorting out, but many manufacturers leave them exposed. All you need is moisture to get to the base of the bulb or even high humidity to cause condensation inside the bulb and presto. Its a good mix for disaster. Also considering there is really no benefit of having the bulb in contact with the water. It will introduce a lot of heat into the system. Also the risk of breakage means the mercury in the bulb will end up in the tank. 

Inefficiency is relative. This is one of my CFL lit tanks. A 40 breeder that runs 8x13watts. My 55 gallon runs a AH supply 2x55 watt setup that was built in 2008. I know the CFLs are not as efficient as the linear tubes especially given the reflectors I have on the 55 watt bulbs. Regardless the CFLs get things done just as well for 1/3 the cost and 1/3 to 1/2 the upkeep of the fixture. They also give the ability of adjustable wattage. T5 HO are great and all, but personally I only feel the need to use them on deeper tanks where you need the intensity and don't want a bulky hood.

That CFL hood was built in Jan 2013 and has been running since then without a bulb failure or replacement, so 15 months at 8 hours a day. Along with a dirt cheap dirt substrate. It still produces more plants then I have time to deal with.


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## Tolak (Nov 13, 2012)

Flear said:


> (and put the bulbs directly in the water).


Talk about a hold my beer & watch this idea.


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## Flear (Oct 5, 2012)

Tolak, only a problem if the glass in the water vs out of the water is different enough break the tube. 

good point though, best to try that out (when i'm ready for it) with a bucket of plain water and whatever protection can be had


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## Mikaila31 (Dec 18, 2008)

Flear said:


> Tolak, only a problem if the glass in the water vs out of the water is different enough break the tube.
> 
> good point though, best to try that out (when i'm ready for it) with a bucket of plain water and whatever protection can be had


You do not need to break the tube for there to be a problem. It can leak current without shorting out the bulb. You just need enough moisture to build up in the ballast. A lot of heating and cooling cycles in a humid environment is a good way to achieve this. Its as smart and great an idea as playing Russian roulette with a cattle prod in a pool. Basically every time you touch the tank is a potential for getting a very painful zap even if the light appears to be working properly. 

You haven't said what you think this will achieve. Normally you want to cast light down into a tank with a bulb and a reflector, that will give you the most light. Submerging the bulb you will cast a lot of light out of the tank through the glass without a reflector. The reflector would have to be submerged as well to be of any real use.


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## Flear (Oct 5, 2012)

to submerge the spiral CFC light, ... as greenwater can get rather dark, all i'm lighting is the top, water flow should help keep the phytoplankton stirred up and moving, but i'm still only lighting up the surface.

putting a bulb in the water i can light up a whole lot more, i'm not expecting much light to get out of the bucket as the greenwater would get even thicker.


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## Tolak (Nov 13, 2012)

You go ahead & submerge that bulb sparky. I'll just wait, at a distance, for you to report back with the results.


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## pop (Aug 29, 2012)

Hello Friends:
This is a funny thread, Sparkie it would take you about 12 or so minutes to make a cfl submersible it would take me 30 minutes iam slow.

All you need is an ole mason jar and lid that had some homemade corn in it, submersible wire and a shrink kit to seal electrical connections and cfl bulb and a socket and silicone. You know the rest.
Have a shocking, laughing happy day!
pop


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## Flear (Oct 5, 2012)

there is very very little i do that is by the books.

reminds me, i forgot to feed my clams ;(


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## avraptorhal (Jan 2, 2013)

The actual measurement spectrum of a specific meter is dependent on the design of the meter. Which is dependent on the specific intent of the use of the meter. 

It could be a wide spectrum or a narrow spectrum meter. It could also include UV and IR wavelengths or not. It all depends on the function the meter was designed for.


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## RSVBiffer (Feb 3, 2014)

Flear said:


> the CFL spiral bulbs i'm going to settle on for growing greenwater (and put the bulbs directly in the water).
> 
> otherwise i consider these bulbs to be inefficient as over half the bulb is facing itself. (so i stick with linear lights)


Flear, I really do not think it is a good idea to submerge an electrical item in water than has not been designed to be used in such a manner, the setup you are suggesting is just darn right dangerous.


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