Monday, December 03, 2012

A Complete Idiot's guide to understand LED

For more such tutorials and fishy pictures, visit my website:

LEDs are the new ‘IN’ in the lighting world and so is in our hobby where lighting is an essentially important. Be it reef, planted tanks or simple fish setups, light is needed everywhere.
We have been using CFLs, PLLs, metal halides, T5s, T8s, T12s etc for our lighting needs but after LEDs have hit the market, they seem to be the best lighting solution. Let’s have a look at some of their pros and cons -

•    Very low electricity consumption.
•    Very high light output.
•    Long lasting components.
•    Economical in the long run.
•    Very small in size.
•    Latest in technology.
•    The wavelength of the LED can be customized according the need by the manufacturer.

•    High initial cost.
•    The cost of other components needed to make a LED light unit.
•    The heat produced.
•    Very fragile. Care must be taken when installing.
And as we all know, hobbyists need a single reason to start something new ;) And we have so many.


Before starting the discussion on LEDs I’d like to explain one thing. PAR - which stands for Photosynthetically Active Radiation.

We have been measuring the lights in our tanks in Watts per gallon.
Let’s just assume there are two tanks of same capacity, say 10 Gallons, but their heights are different. One is 14” in height and the other one is 9” in height. If we put the same light at the same height over both the tanks, would light reaching the bottom of the tanks be the same ??
NO… It would never be the same. So, its time we stop using WPG in our fish-talks.
Let’s discuss PAR in a little more detail now.
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 stands for “photosynthetically active radiation” - the radiation (light) that is used by plants for photosynthesis. The units of PAR are micromoles 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.

Don’t worry it’s not that complicated. Our eyes see the yellow and green part of the light spectrum  which means our eyes are sensitive to yellows and greens. Plants are very sensitive to reds and blues, so they absorb most of the light in reds and blues, but less sensitive to yellows and greens, reflecting a lot of the light in these colors. That is why most plants look green or yellow. [We see colors because the thing we see has absorbed all the colors in the spectrum except the color we see].

How to measure the PAR! There are meters available in the market just like meters available to measure voltage, current or pH. Nowadays the light manufacturing companies are promoting their products by advertising the PAR values of their lighting products.

PAR value of any light decreases gradually as the distance from the light source increases. That means the nearer, the more PAR and the farther, the low PAR.

Now you may ask how much PAR is like 4 WPG and what PAR is like 1 WPG. We started this hobby by learning the light in WPG. It’s same as learning the difference between rupees and dollars. You know $1 is 50 Rupees but still, being an Indian your mind is not tuned according to Dollars (Happening to me right now :/). So to tell you- 

10-30 micromoles of PAR- Low light
30-50 Micromoles of PAR- Medium light
50 and above- High light.

This photo explains it very well. See the green and yellow (500-600 nm) are the lowest points. Remember, they’re not ZERO. It’s not like plants DO NOT absorb Yellows and Greens. They do but very small in comparison to Blues, Violets and Reds. Red is said to be a helping hand in growing algae. So an ideal spectrum to use in the aquarium would have low Reds, Greens, Yellows and High Blues and Violets. You can keep Reds on the high notes but then you must have good CO2 and good fertilizers to keep up the balance.






Now let’s talk about LEDs. I’m again reminding you that I am writing this at a very basic level. I won’t go deep into the semiconductor world. The info one needs to know to understand the LED lights for aquariums is all I want to write.

LEDs are very small lights. They have a positive and a negative terminal. They are very small to solder the wires on. So the manufacturers mount the LEDs on stars. This gives it enough space to solder the wires and to put the LEDs on the heatsinks. Size of the stars is generally 20mm.
The photos will explain it to you-
This is a LED.

Now let's see how a start looks like-

And when the LED is mounted on the start it looks like-

This would be the final product you would be getting. This is how the LED, we now, looks.


How Many LEDs to use for my tank?

When building a LED light unit for your tank, the first question comes to your mind is- how many LEDs to use. The rule of thumb says-

Numbers of LED to use = The area of footprint of your tank / 22.

Let’s say your tanks is 24”x12”x14” [LxBxH] the area of the base would be- 24”x12”= 288 sq inch.
Now to calculate the no of LEDs to use- 288/22= Around 13 LEDs would be needed.

What colors do I need?

White LEDs come in 3 colors-
  • Cool White (Color Temp- 6500K),
  • Neutral (Color Temp-5000K)
  • Warm White (Color Temp- 3500K)

Don’t get confused between the wavelength and color temp. Wavelength is measured in nm and the temperature of light is measured in K Kelvin.
For planted tanks, generally we prefer Cool white light. But if you want to make a LED unit for your discus tank or fish only tank, Warm white would be the best choice as it gives the perfect yellowish color and accents the color of fish [Just like under our ‘Hitachi’ tube light, goldfish used to look pink ;)]
As we have discussed earlier, an ideal light’s spectrum would have low Reds, low Greens and Yellows and high of Blues and Violets.
So to mimic this ideal condition in our DIY-ed LED unit, we mix some colors with cool white. Like- Royal Blue which have the wavelength of 465nm to 485 nm.

Cree XP-E Royal Blue color parameters-

Or some Violet LEDs which have the wavelength of 410nm to 420nm.

Now let’s see the spectrum and the PAR data graph of some combinations of LEDs-

Cool White + Neutral White. As you can see the Greens, Yellows and Reds are quite high than the Blues and Violets.

Cool White + Warm White. Compared to the last combination of Cool white + Neutral White, this has much lows of Blues and Purples.

Now see the combination of Cool White + Warm White + Royal Blue. The Blues and Violets are very high and Greens, Yellows and Reds are very low.

Now guess what would be the best spectrum for your planted tank!!
Yes! You’re right. The last one, because it has low Reds, Greens and Yellows and has high Blues.
The one I’m gonna build would also have the same combination of Cool whites, Warm whites and Royal Blues.

How to practically build a LED unit.

You would need-
•    Heatsink
•    LEDs
•    LED optics
•    Power supply drivers
•    Fan for the heatsink (Optional)
•    Dimmer/ Controller (Optional)
•    Wire
•    Solder cable
•    Solder Iron
•    Thermal Adhesive or thermal grease.
•    2 AA batteries to test the LEDs


Prior to start telling you what it is, just see how it looks like-

It has a lot of fins or wings which makes its surface area way bigger than just of a solid piece or a plate of the same material. Generally Aluminum is used to make the Heatsinks. But now hard anodized heatsinks have also hit the market.

The black one shown above is hard anodized and the white one is just Aluminum heatsink.

There are 2 ways to mount LEDs on the heatsink-

  1. Thermal Adhesive- It’s like fevikwik. Just put a drop of it on the back of LED and paste it. But the joint is permanent. You won’t be able to remove or replace the LED.
  2. Screws and thermal grease- Drill the holes on the heatsink. Put some Thermal Grease on the back of LED and screw it down. We put the grease so that the heat from the LED can transfer to the heatsink already. Any air gaps could make your LEDs very hot and damage it.

Some people put fans on their heatsinks. How to know if you need a fan on your heatsink or not.  Just touch your heatsink when the unit has been on since 2-3 hours. If you can touch it, you don’t need a fan. But if you can’t touch it, you need a fan.

LEDs have some characteristics. Like we buy our CFL bulbs by their wattage, we buy LEDs by their Forward Voltage and Maximum Drive Current.
Like- A Cree XT-E Royal Blue LED has Forward Voltage of 3.0 V, wattage of 3W and Max Drive current of 1500mA.
It means the maximum current you can give to this LED is 1500 mA and when put in a series, after every LED you’d see a drop of 3 Volts in the Voltage.

LED Optics-
 Most LEDs have a light angle of 120 degrees. Which means the light would spread in a cone of 120 degrees. So to concentrate the light over an area we would need some lens or optics. Optics are named according to their concentration capabilities - 20 Degrees, 40 Degrees, 60 Degrees, 80 Degrees.
Power Supply Drivers- 

LEDs work on DC current. So the drivers convert our household AC current to DC to light up the LEDs. They are characterized by their Max Drive Current and total Wattage.

For eg. Inventronics 40w driver - 700mA. Its total wattage is 40 watts so it can light up around 12 LEDs of 3W each. We leave 4 W as a margin. The 700mA is the Max Drive Current. You can use 700mA driver to light up a LED which has Max Drive Current rating of 1500mA. But you cannot use 1500mA rated driver to light up the LED with 700mA Max Drive Current.

Now, Just to talk a bit more about the drivers, lets take a new LED which is more efficient than the previous XP-G or XT-E. Cree XM-L. It has Max. drive current of 3000mA. It's upto you how much light do you want from this LED. If you put 700mA driver, it will give low light, Gradually if you increase the input current from the driver, the light output will increse. Lets see it's graph-


Dimmer/ Controller- 
Just like we have controller for our ceiling fans, you may put dimmer for your LED lights. These are nothing but potentiometers. Generally we use 10 ohm dimmer.
But if you want to go fancy (which I wanna go :D) there are sunrise sunset dimmers available. You may set the time when your LEDs will start lighting up from 0% and when they would go 100% and the same of 100% to 0%. A lot of options are coming in the market nowadays.

See the one I'm gonna use here- dimmer youtube video
Wires, Solder cables, and Solder Irons- 

You all know what their uses are.
Before concluding the bibliography, I'd like to answer the question which still is buzzing in your mind(yes, I know it all ;) )- "How does a finishe LED light unit look like ?"
So, check this vid out and you will come to know- WIfe approved DIY LED unit 

I’ve read this information in past months from the following links and I thank them all. Specially Milad from, Hoppy from TPT, redfishsc from TPT, the blondskeleton from TPT.
This article is written for the sole purpose of understanding LED lighting solutions for aquariums. It is based on what I have read and learnt from various sources. In case something goes differently or unxpected, I am not responsible. All the links that I have read to write this article are mentioned. All the photos are either from the internet or from the links that I've posted. They are the property of their actual awner. I've posted them here just for the information. In case something is not included, please let me know and I will include it.
Thank you for reading this. In case you see something wrong in here, please drop a comment and I'll update it.

The next blog I wrote after this blog can be found here-
Link on TPT
Link on


  1. Very nice article. Can we put it on our web site You would be given credit for writing the article as the "author" and we would link back to this site as well. We are still getting the site together but want good informational articles in one place for easy reference. And this is a great article.

    1. Thank you :)
      Yeah sure you can put this on your website.
      Just to tell you, I also have my website dedicated to betta beginners. Have a look -

    2. Great article, may i use this in my local forum, greets from Turkey.

    3. Hi Mahir. Yeah sure you can use the article in your local forum. As long as you dont forget to include the link back to this page, its completely fine to me :)

  2. Very nicely written Sumer :)
    One doubt..
    Numbers of LED to use = The area of footprint of your tank / 22

    now my tank is 36x18x18, so that would be 36x18/22= 648/22 which gives me a number of 29.5.. lets round it upto 30.

    Now I must use 30 LEDs for my tank.. my doubt is, what should be the wattage of each LED?

    1. Thank you Bhashya :)
      Generally the LEDs which are used in our hooby are 3W LEDs. But its not the wattage which decides the light output of the LED. It may happen that in near future we get to see LEDs more efficient than the ones available right now and which would use only fractions of a watt. So while selecting the LEDs you don't see the wattage. You see the PAR data of the LED. Like I said in the article, watts per gallon WPG is dead now :)

    2. You check for the wattage only when you select the driver for your LEDs.

  3. Great ! should benefit all Aquatic gardeners.

    1. Thank you Subodh ji :)
      Glad you liked it

  4. sumer sir i am building a 60”x18”x22” LxBxH.... from the above calculation i need 49 leds of 3w each but to be on a safer side i am thinking to go up to 55-56 led my real question is what should be the combination of Cool White + Warm White + Royal Blue for my setup if i opt to use around 55-56 (correct me if i have to reduce or increase the no of leds) and if u can help me with arrangement/placement(diagram will help) of the leds on the heat sink and also the dimension of heat sink i will need ... thanks a lot in advance

  5. Hey Sandeep- Just wait for my next blog post. It will surely answer all your questions :)

    1. Hi Sumer, If you have published your next blog post, answering questions asked by Sandeep then please provide me the link. I also have same questions regarding combination of LEDs, par value of each LEDs, placements of LEDs for my 36x18x18 tank where I need 30 LEDs. Thanks.

    2. Hi Gaurab,

      Yeah I wrote it but not on my blog this time. It's on other websites. Here are the links-


      Hope it would help you guys :) Lemme know if you wanna know something else :)

    3. Hello Sumer,

      That was awesome DIY post. A complete step by step guide. Thank you. But I still have one question. I need 30 LEDs for my tank. Cool whites, Warm whites and Royal Blues for planted tank. But what should be the ratio? 10 of each colour? In your project you have used red LEDs. Do I need to put in Reds? If so, how many?

      Thanks in advance for your guidance.

  6. Hello! Thanks for your guide, it cleared some questions in my mind.
    But I have to ask you about this phrase:
    "You can use 700mA driver to light up a LED which has Max Drive Current rating of 1500mA. But you cannot use 1500mA rated driver to light up the LED with 700mA Max Drive Current."

    The leds will draw the highest current they can handle IF you provide the correct voltage, isn't it? A 1500mA rated driver CAN provide 1500mA at the available voltage range, but it won't if the leds don't want it. Let's say 3 leds with 3.3V forward voltage and 1000mA current, using a 9-42V 1400mA power supply will draw.... 1000mA current...?
    With a 12V 1500mA constant current and a 2.2 Ohm resistor, the circuit will draw.... 1000mA current...(the resistor idea won't work with a range voltage power supply I guess...)
    Is all these right? Please advice.

    1. Hi George,
      What you're saying about the current maybe true.
      But according to what my friends or people I got inspired from have experienced, If you put a 700mA LED on a 1500mA driver, it'll burn your LED. I discussed your question with a friend and he said- "How will LEDs decide what current do they want !!"

      You put the LEDs in series connection where at every LED you find a Voltage drop but the current remains same throughout the circuit.
      BTW this is what I've experienced. If you come to know about the accuret information, dont forget to comment here.
      Thanks for the coment and sorry for the late reply.

    2. Hi again, thanks for the reply!
      I want to clarify that I'm on the search to replace my CFLs with LEDs and I have NO real experience with them, except for some low-power LED strips.

      The LEDs will decide what current they want using their... Resistance!
      Given the exact voltage they need, the current will get to the top of LED's specs I=V/R. But the power supply MUST be capable of providing that maximum current, or else it will provide it's maximum available current.

      But all LEDs connected must work at the same maximum current. Let's say we have two LEDs one with maximum 750mA and one with maximum 1500mA, working at the same voltage and we connect them to a power supply capable of 1500mA. The total resistance of the circuit(in series) draws, at the given maximum voltage, will be 1125mA. So the one LED will burn and the other one will underfunction(as long as it'll be working!).

      All these are just my theories, I definitely trust you that the LEDs will burn.
      And these theories are not capable of answering ANY question about the multi-range-voltage power supplies....!

    3. Just wanted to correct the above (and I realise this is an old thread but the information is misleading).

      LEDs do not know what current they want - they cannot limit the current flowing through them which is why we use CC (constant current) sources which stop the LED from drawing more current than they are rated for. What this means is their 'resistance' to current decreases as the junction temperature increases which allows higher current casing higher temperatures until they burn out. Do not connect your LEDs to a voltage source.

      The LEDs in series do not necessarily need the same maximum current rating but you should select/set the driver based on the lowest rated diode in that series - cater to the weakest link.

    4. Just wanted to correct the above (and I realise this is an old thread but the information is misleading).

      LEDs do not know what current they want - they cannot limit the current flowing through them which is why we use CC (constant current) sources which stop the LED from drawing more current than they are rated for. What this means is their 'resistance' to current decreases as the junction temperature increases which allows higher current casing higher temperatures until they burn out. Do not connect your LEDs to a voltage source.

      The LEDs in series do not necessarily need the same maximum current rating but you should select/set the driver based on the lowest rated diode in that series - cater to the weakest link.

  7. Awesome article......thing is you kinda touched on heights. What if Im gonna put LED's on a 20g tank. I can follow your formula the only part is what if its a 20 tall and not normal. My worry about following your (amazingly easy) formula is it doesn't take height into account at all.

    1. Yeah you're right. Height would definitely make a difference. But this article so solely intended to educate the idiots. So no hi-tech stuff. LOL. Just kidding..

      But yeah I should think up on this. There must be something you know.. Like if you're going low on the height you will reduce the multiplication constant by some other number. Will have to do more practicals on this. Thanks for bringing this out.


  8. I could use information given to figure out par value if I had a rather expensive par meter.

  9. Great article but i have a question about leds. i was used your formula and i need 22 led for my tank and here is my question.. i guess these leds are 3 w but i cant use 3 w leds for cooling issues. I havent enough space for big heatsink and fans.How many 1 w leds should i use instead of 3 watts and what is color rate between coolwhite/warmwhite and royal blue ?


  10. The only thing left out is where to get all the items to build a LED light.

    1. There's a link at the top of this article. Check that link out. It would tell you everything about making a unit like this.
      I bought all the stuff from

  11. Nice article bro. My next display setup is now definitely going to have LEDs.

    1. Thank you :)
      All the best for your next project.

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  14. Hi there!

    I was going through ebay listing and while some Chinese producers have enticing offerings I'm not sure what to think of them, in terms of durability. Additionally I think there isn't a heat sink (at least to my untrained eye). Could you be so kind as to have a look and help me make a call? :)

    1. Hey mate,

      To me it looks like a multi chip LED. Multi chip LED means it has many small small LEDs which make it a big LED chip. recently came up with a similar product- ( ). They need heatsinks BTW. you will have to buy a heatsink for it. They are good but I am not sure how durable it'd be.
      All the best :)

  15. I have used similar LEDs on a 20g long tank (30x12x13) and I only used 8 total LEDs (6x cool white and 2x royal blue) and had some serious algae issues. They were 3W each and provided pretty good light, but I'm thinking it was way too strong for this sized tank. I have now tried again with 1W LEDs. And so far, it's been better with algae control and the look hasn't suffered too much. 3W is probably good if you have a high tech tank or corals i guess.

    1. To tell you the truth, its not just the light which makes algae grow.
      A happy algae free tank has the proper balance of lights, flow, ferts, CO2 and light. If any one of these things get out of proportion, you will have algae in your tank. Doesn't matter is you use, PLL, 1W LED, 3W LED, CFL or MH.

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  19. Yes that's true that it is not easy to keep a sea aquarium. But to keep a beautiful things always need some cares. So I always take care of my home aquarium specially on visual looking. So recently I am use a reef led light in that aquarium which was ordered from

  20. Hi from sunny Macedonia.
    I have one question. I'm planing to start heavily planted aquarium. Balance of apprentice between plants v.s. fish will be 60:40 in favor of plants. According to your equation for led needed, I calculate that I need around 45 led. According to current prices that is around 180$ only for the led. So this is over my budget. I was tinkling to use only royal blue led and for other lighting to use something cheaper (cheep led, or other kind of laps). Do you have any suggestion how to make this combination.
    All best

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  31. Namaste Sumer ji .
    This is an awesome and informative post.
    From your experience how would a high power leds (3W) as explained in your blog compare to LED light strips, like below

    The above led strip outputs 50W/5m, i.e. 1m = 10 W ~ 400 lumens/m ; WPG is an outdated rule, just used it for calculations. 1m has 60 LED's with each LED ~0.6 W.

    Now if one were to build a plant friendly spectrum using such strips, i.e. 4 Cool White(6500K) + 3 Warm White(3000K) + 2 RGB strips(~ 324 led's) and power them with a 5A power supply, would they be decent equivalent to the LED you have built and explained in this blog?..


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