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Here's a recent article, which covers all the important aspects of aquarium LEDs, including PUR, and the science behind it. The website also reviews many of the more popular aquarium LEDs out.

LED Aquarium Lights,[censored]Lighting; How they work, DIY | Aquarium Article Digest

Here's a good review as well.


TMC AquaRay Vs. Build My LED | Marine Aquarium LED Study
Has Trigger mentioned that he wrote this review article? A bit disingenuous to post it as a reference without disclosing his bias.
 

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Discussion Starter · #442 ·
Did anyone ever check out the Aquael Leddy Tube 8000K? It looks interesting and I'm considering the 16W, but I can't find any information about PAR.

I need some more light for my 250l tank to supplement the 2xHagen Glo 39W, but I can't decide wether to buy another one or put in LED.
Wow! You must want really high light! A two bulb Hagen Glo light should be enough to grow most any plants. That size tank, with two 39 watt T5HO bulbs is sold as a reef tank, and reef tanks use a lot more light than planted tanks.
 

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The K value is a number that represents what the bulb will look like to our eyes. 8000K is decidedly toward the blue. Usually planted tanks do well with some of the red wavelengths and some of the blue. Usually about 6500K is about as high a K value that works for plants.
 

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@;
The K value is a number that represents what the bulb will look like to our eyes. 8000K is decidedly toward the blue. Usually planted tanks do well with some of the red wavelengths and some of the blue. Usually about 6500K is about as high a K value that works for plants.
That's interesting being that ADA says their bulbs are 8000K and yet seem to grow plants well. My Kessils have an adjustable range of 6000 to 9000. I have them set in the middle of the range which, I would think, puts me at 7500 and I have no issues with growth. It makes me wonder how accurate the Kevin ratings are from all of the manufacturers.
 

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That's interesting being that ADA says their bulbs are 8000K and yet seem to grow plants well. My Kessils have an adjustable range of 6000 to 9000. I have them set in the middle of the range which, I would think, puts me at 7500 and I have no issues with growth. It makes me wonder how accurate the Kevin ratings are from all of the manufacturers.
Kelvin for certain types of lights (fluorescent,led, and MH for example) is an average.. therefore there is a very broad number of ind. "colors" and different intensities of each color that can create the same K value..
K and CCT are the same sort of..
The correlated color temperature (CCT) is a specification of the color appearance of the light emitted by a lamp, relating its color to the color of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K).
The correlated color temperature (CCT) designation for a light source gives a good indication of the lamp's general appearance, but does not give information on its specific spectral power distribution. Therefore, two lamps may appear to be the same color, but their effects on object colors can be quite different.
http://www.lrc.rpi.edu/education/learning/terminology/cct.asp
 

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Does anyone know what the PAR is like on the updated Fluval Spec V? Thanks.
 

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Would depend on how high over the tank the fixture will rest.
With PAR ,which is all plant's really care about,inches matter.
I think the fixture will/would be too wide to rest on the tank,(I have four tube fixture)so ... Par will be different as the light fixture is raised.
 

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Hi all you experts. I am here on this old post because i am unable to get an affirmative. So i want to do a diy led. My substrate is dirt and aquasoil mix and capped with sand. My tank is 6ft x 1.5ft x 1.5ft. I want to do a dwarf sag carpet and some swords and crypts. My intention is to put about three or four 4ft t8 led tubes. Staggered along the length to cover the 6ft. No co2 no reflectors needed. Will that work. Or do i need more or less tubes. The tube available to me are 20w 6500k cri 75 and direct 110v so no ballasts neither. The tubes are similar to these
https://www.walmart.com/ip/Yescom-1...e-Replacement-Lamp-Bulb-Milky-Clear/104669279
 

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When light shines into an aquarium the air-water interface slightly focuses the light. Beams off center are refracted towards the center. This is why the PAR around the center of the tank goes up when you add water. Near the glass at the front, back, and ends, there is considerable reflection of light back into the tank from the glass-air interface, which increases the PAR near the glass. But, if the glass is less than perfectly clean on either side of the glass the amount reflected back into the water is decreased. As I recall I did those PAR measurements in a 10 gallon tank, which I didn't take pains to clean thoroughly. The glass must have been non-uniformly dirty. This was a few years ago, so my memory of that isn't perfect.

I don't have either a 30 inch long tank, nor a 24 inch long light to do PAR tests with. Most of the data I have comes from others who either post it or PM it to me. Someone with the right tank and light, and access to a PAR meter, needs to do that testing. One thing I do know is that if you raise the light far enough above the top of the tank a short light can light up a tank well enough for our purposes. In fact one good way to light a tank is to use a short, but very bright light (4 bulb T5HO, for example) suspended a foot or more above the tank. That greatly reduces the difference in PAR between the water surface and substrate level, and gives relatively uniform light over the substrate.
Considering a tank of 24x12x18 inch and 22 gallon, how much CFL and of how much watt would be required??

Thanks in Advance
Jim
 

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Before any discussion of aquarium lighting can proceed, first we have to debunk the myth about “watts per gallon” being a measurement of light intensity.

When the only practical source of light for a planted tank was T12 fluorescent tubes, someone decided that the way to pick out the best lighting was to figure out the “watts per gallon” that were needed to grow various types of plants. This would make sense if we could pour a teaspoon of watts of light into a tank, and get a light concentration of X watts per gallon of water, just as we pour a teaspoon of potassium nitrate in the tank to get a nitrate concentration of Y mg per liter of water. But light is nothing like a chemical - you can’t pour it anywhere, you can only shine it on something. That alone should debunk “watts per gallon” as a measure of light intensity.

But, there is more: Let us assume we have two 20 gallon tanks, with 40 watts of T12 Fluorescent light on each one - 2 watts per gallon. One tank is a 20L and one is a 20H. The 20L tank is 12 inches high, and the 20H tank is 16 inches high. If the fluorescent light sits right on top of each of the tanks, the light on the 20H tank is 4 inches farther from the substrate - 33% farther from the substrate. Because light intensity drops approximately proportional to one divided by the distance from the light squared, the intensity at the substrate in the 20H tank has to be about 56% of that at the substrate in the 20L tank. That alone should debunk “watts per gallon” as a measure of light intensity.

But, there is more: Let us assume we have two 20H tanks, one with a 40 watt T12 light sitting on top of the tank, and the other with the same light hanging 12 inches above the top of the tank. Again, because light intensity drops approximately proportional to one divided by the distance from the light squared, the intensity at the substrate for the tank with the light hanging 12 inches above the top of the tank must be about 32% of the light intensity of the tank with the light sitting on top of the tank. And, that alone should debunk “watts per gallon” as a measure of light intensity.

So, that is three strikes against “watts per gallon”.

But, there is more: Let us assume we have two 20H tanks, one with 40 watts of T5HO light, from a Tek light fixture, the other with 40 watts of T12 light. Anyone who has looked at both a T5HO bulb and a T12 bulb, when they are lit up, knows that the T12 bulb can be stared at without distress, but the T5HO bulb causes some temporary blindness if you look at it for more than a few seconds. The T5HO bulb is much, much brighter, and has to give much more light at a given distance than the T12 bulb.

“Watts per gallon” is dead!



PAR

Light intensity can be measured in lux, which is the intensity as perceived by human eyes. Or, it can be measured in PAR units, which is the intensity as perceived by plants. PAR is an acronym for “photosynthetically active radiation” - the radiation (light) that is used by plants for photosynthesis. The units of PAR are micromols of photons per square meter per second. So, a PAR of 1 is one millionth of a mole of photons striking a one square meter area every second.

Human eyes see the yellow green area of the spectrum of light very well - our eyes are very sensitive to yellows and greens, but we see reds and blues much less well. Plants are very sensitive to reds and blues, absorbing most of the light in those colors, but less sensitive to yellows and greens, reflecting a lot of the light in those colors. That is why most plants look green or yellow.



MEASURING PAR

The best way to find out how much light intensity we have in our planted tanks is to measure it. To do that we must use a PAR meter. A few years ago the only PAR meters available cost a few thousand dollars apiece. Now there are much cheaper PAR meters available.

You can buy a Quantum PAR meter, Model MQ, for $329 plus shipping. That is a near laboratory quality meter, with a guaranteed calibration, which can be re-calibrated at the factory when needed. It is the Cadillac of hobbyist PAR meters, usually bought only by clubs, where many members can use it.

A lower priced version of the Quantum PAR meter is just the sensor, Model SQ, for $139 plus shipping. To use this you need to either use a good millivoltmeter, which gives the best accuracy, or a cheap lux meter, like the Mastech LX1010BS, from Amazon.com, at about $20 plus shipping. Used with the lux meter you need to do your own calibration. You can use your digital multimeter, with a millivolt scale and the sensor, to determine the PAR from a light at a fixed distance, then connect the Mastech lux meter to the sensor to see what the meter reads at that PAR. This gives you a calibration constant for that combination of sensor and meter to convert lux to PAR.

Still cheaper is to buy one of the DIY PAR meters made by Mistergreen and/or O2surplus, for about $60. These are calibrated, and the meter reads in PAR units, but they may not be available when you want to obtain one.

Cheapest is to buy a Mastech LX1010BS, at $20 plus shipping, and modify it yourself per Convert Lux meter to PAR meter? but you have to calibrate this yourself. However, the total cost should be $35 or less. If the Quantum PAR meter is the Cadillac of PAR meters, this is the refurbished Volkswagon bug of PAR meters.

SELECTING A LIGHT

Before we can even start to measure the light intensity, or PAR, that a given light will provide on our tank we first have to obtain the light. It may seem that we have to be working blind when we make this selection, given that knowing the “watts per gallon” won’t tell us anything about the intensity we will get. But, because there are now many PAR meters in hobbyist’s hands, we now have a lot of data on how much PAR we can get from several different lights, made by several different manufacturers. More data becomes available every month.

Today we can chose one of several different types of lights:
T5HO fluorescent lights with 1,2,3,4, etc. bulbs
T5NO fluorescent lights
T8 fluorescent lights with 1,2,3,4, etc. bulbs
PC power compact fluorescent lights with 1 or 2 bulbs
LED lights of many configurations - DIY or ready made
CFL screw-in fluorescent lights - DIY

For each of those types of lights a chart can be made showing the PAR produced by the light versus the distance from the light. These charts show the light intensity as measured without a tank of water being involved - just the intensity as measured in air. This is necessary to avoid the many variations in intensity caused by the tank dimensions and the cleanliness of the tank glass, both of which can have about a 10-20% effect on the intensity.





LOW LIGHT, MEDIUM Light, HIGH LIGHT

I don't believe there is any consensus about the definition of low, medium and high light. But, here is my definiition, subject to, and almost certain to change:
Low light - 15-30 micromols of PAR - CO2 is not needed, but is helpful to the plants
Medium light - 35-50 micromols of PAR - CO2 may be needed to avoid too many nuisance algae problems
High light - more than 50 micromols of PAR - pressurized CO2 is essential to avoid major algae problems

The following charts show the data that I now have for various lights. As I get more data I will keep updating the charts and adding new ones. If you want a light that isn’t included in the charts you can study the reflectors used in the light you want and compare them to the photos following the charts to see which charted light is closest to the one you want, to get a rough guess at what PAR that light will give you.

Fluorescent tube lights produce about the same light intensity for any length of tube, from about 24 inches to at least 60 inches. The longer bulbs are proportionally higher in wattage, so that the bulb wattage is mostly a measure of the bulb length, not the bulb brightness. For bulbs shorter than 24 inches, this may not be true.

CAUTION: Not all lights use a true, full power HO ballast. Some cheaper models use lower power ballasts, and will not produce as much PAR as those with good ballasts. Compare the chart for the FishNeedIt lights to the others for an example.






One layer of window screen over the bottom half of each bulb, right on the bulb, drops the PAR by about 30%






See LED Lighting Compendium for much more information on LED lights.

Photos of various reflectors used in T5 lights:




Hagen GLO 2 bulb light


ATI 4 bulb T5HO


Home Depot 2 bulb Diamond Plate Shop Light - note the reflections of each bulb.



One bulb T8 light with fairly good reflector


Aquaticlife 4 bulb Light
Science! Thank you for sharing your knowledge. While I did read your post, I have some questions remaining about my setup specifically that I was hoping you could help with. I understand you gained this info with a 10g tank, so my questions about my 20g are purely theoretical. I have a 20g H, 16 3/4 inches high so I’ll estimate 15 inches from substrate. I’m using a single bulb Sunblaster brand T5HO 39 watt light with a nice reflector over glass.

1030135

1030136


Using your chart I went off the green dashed line “Catalina T5HO one bulb” since that seemed to match with what I have. It seems like the PAR would be 100-60 with no water in the tank, correct? And you said that with water that will decrease the PAR by 10-20% depending on the location in the tank and depth of water. For the chard you used 5 inches of water, so with 15 inches of water in my tank would the PAR be decreased by 20% or more like 3 times that ? Also, would you let me know how much raising my light a few inches would now affect the PAR?

Again, thanks so much for your post. I feel like I have learned so much more from your single post than reading countless other articles online
 

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Hoppy no longer posts here afaict.
Try Tom Barres barreport.
 
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