Light Emitting Diode

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Introduction

Light emitting diodes are referred to as LEDs for short.


Standard vs High Power

Perhaps what throws people today is the concept of what L.E.D.S we refer to for tank lighting. There are many different types of L.E.D. available today but for the most part, they fall into 1 of 2 categories, High Power and Standard. The ones we like are High Power, these are in some cases as potent in their output as some lasers and thus require handling with the same degree of caution. These physically tiny lights are able to do damage to your eyes so please please treat them with the respect they deserve!

During your search for the perfect lighting source, you will no doubt come across lighting systems like these: (insert low power led pic here). These are cheap units, packed undeniably with a large number of L.E.D.'S, for remarkably low power usage. These are excellent lighting options for tanks with fish ONLY.

If your intention is to keep corals or anemones then steer clear of the above. You need to look at High Power L.E.D.'S. Some of these setups surpass Metal Halide light output with much less energy used. So now that we’ve got that out of the way, you have 2 choices, do you buy a pre-built unit or build one yourself? Hopefully the below information will help you decide what is right for you.

Pre-Assembled Units

This is pretty self explanatory, pre build L.E.D. lights for your tank. One major advantage of pre-built units is warranty. If we’re being totally honest here, these light sources are by no means cheap initially, so understandably you want some piece of mind about your investment.

Another important fact to keep in mind, a lot of pre-built units come with some form of lighting control. This can be as simple as a switch on the unit itself all the way up to multi-channel dimming to create unique lighting effects that other lighting systems simply can’t hope to accomplish, including storm and moon effects to name a few.

These units also tend to look quite respectable or even attractive, which is something that many DIY units fail to accomplish. If this all sounds perfect for you then I think it’s clear which way you want to go.

Do It Yourself (DIY)

If you go down this road, let me warn you right from the get go, ELECTRICITY KILLS, get it wrong and your potentially dead or injured. I cannot stress enough the importance of being absolutely certain about wiring with regards to mains power and I believe it is mandatory in most or all states to get anything you build for mains power checked by a ticketed electrician. So do it.

Now if I haven’t scared you off, it’s not all doom and gloom, in fact, going DIY can be very rewarding and potentially limitless in simplicity or intricacy.

Some of the positive reasons to go DIY are: you choose what goes into your build, your able to use the latest and greatest parts at the same time or before the manufacturers do, the system can be infinitely upgraded and if need be, repaired by simply swapping out old or failed parts, you know what parts to swap out because you put them in place to begin with. These a few of the reasons I could think of off the top of my head, and believe me, there are more…

So now that you’re steering towards DIY, let me go over some of the requirements for your build.

Cree are the most well known in the aquarium hobby, and are unbeaten in terms of performance and cost so far. If your looking at making your own LED light fixture then you need to know it WILL NOT be a cheap endeavour, but there are far greater saving to be made in the long run. As far as whats been discussed on the forums, the internet is the cheapest place to get high power led's, and usually go for between $6-8 for the 3W models which are most widely used for this purpose.

The Essentials:

The race is on for the title of number 1 LED manufacturer. This is great news for us as it means there are heaps of options coming on the market every other day to help us build the best possible lighting system. It also means that costs are making their way down if you want to get your hands on product that is 1 or 2 generations old. There are currently 3 main contenders in the race and 1 clear winner.

Luxeon started it all with the first lighting class led and soon Seoul came on the scene in competition. Recently though, Cree has emerged, seemingly out of nowhere, as the clear technological champion of the day. At this point in time, to recommend a build with another brand seems irresponsible as Cree's L.E.D.'S suit our needs almost perfectly. In their efforts to get higher efficiency and cleaner colours, they have inadvertently created a light source with almost perfect spectrum for our needs, with low levels of red, green and yellow, no UV or infra-red, and high amounts of blue, these tiny power houses make the perfect habitat for happy tank mates.

PSU

This is pretty basic, any AC/DC power supply will do but there is some maths involved so it maybe best to do some research into what PSU you can actually get your hands on before you get to far into your build.

So now we get into the maths which is where the fun starts.. if you like maths…

To begin with, let me introduce you to some basics about electricity; any energy that is not used must be dissipated somehow, this is why I would like to recommend that you try and get a PSU with adjustable output (even +/- 1% will help but aim for +/- 10% or more if you can get it). This energy is normally dissipated through the driver so keep that in mind as if calculated incorrectly, the driver will get very VERY hot!!!

Now the maths: now lets say you want to build the most basic of circuits, 1 led illuminated.

There are three things you need from your PSU, Enough voltage, enough wattage, enough amperage.

So in your simple circuit, you have 1 led, 1 driver and 1 PSU. A common Cree forward voltage (abbreviated as VF in Cree data sheets and represents to required voltage to turn the led on) is 3.5v. Now a driver will also require VF anywhere from .5v up to 3v or more. For the ease of this example, we’re going to assume the forward voltage of the driver is 2.5v. so to run the led and driver, the PSU needs to be minimum 6v DC because 3.5 + 2.5 = 6v.

Now your led also requires a lot of amperage, this is what can knock a lot of small PSU’s out of contention, currently, a common figure for Cree L.E.D.'S is 1amp (amp is the abbreviation for amperage, also a capital ‘A’ is commonly used to represent whole amperes while ‘ma’ is used to described thousandths of an amp, i.e. 1000ma = 1A) so you PSU needs to be able to handle 1A constant draw.

Finally, your LED requires wattage, roughly 3 watts actually, so when selecting your PSU, don’t forget to take this into account either. When it comes to wattage however, it’s a little bit different, it’s best to over rate the wattage on the PSU as cutting it too close can make the PSU get hot (kind of like running your car at 6000rpm all day).

So to recap, to drive our 1 led, we need enough voltage for the led and driver, and enough amperage and wattage for the L.E.D., perfect, read the drivers section to learn about setting up large led arrays.

Driver

No doubt, after reading the last section your asking wtf is a driver. Well its like this, unlike other electrical devices that run on voltage as their regulator (much like an electric motor, apply more voltage, motor goes faster), L.E.D.'S run on current or amperage. The problem is that most PSU’s are designed with voltage regulation in mind, so you need a constant current driver (often abbreviated to just driver) to maintain a stable amperage for the led. This ensures you get maximum longevity, performance and efficiency from your L.E.D.'S.

Now you’re thinking hang on, that’s all well and good but I want to use 6 L.E.D.'S, or 12 L.E.D.'S, or 120 L.E.D.'S etc. So now we’re getting into the part that confuses people the most, parallel and series.

For the following example, I’m going to use a 24v 6.5A 150watt PSU, these numbers are important so keep them in mind. Each driver can run more than 1 led in series, the number of L.E.D.'S is determined by the maximum input voltage of the driver minus the forward voltage or ‘voltage drop’ of the driver. For this example I’m going to use the specs from a well known driver called a buck puck with a maximum input voltage of 32v DC and forward voltage of 3v.

So, time for some more maths, we start with voltage, we have 24v available minus the 3v “dropped” to run the driver, leaving us with 21v. The remaining voltage available is divided among the L.E.D.'S so 21/3.5=6 so, according to our maths, from our 24v PSU using a buck-puck we can run 6 L.E.D.'S exactly in series with 0 wasted voltage to dissipate as heat. This series configuration is often called a string or L.E.D.'S.

Yay, but you say I want to run more than that, and rightly so. Now we have already maxed out the voltage on the PSU but according to what we already know about or L.E.D.'S from earlier notes, we’ve only used 1 of our available 6.5 amps and at 3 watts per led, 3*6= 18 watts of our available 150 watts of power. So we have another option, we setup another string of L.E.D.'S beside our previously built one. This means we also need another driver and another 6 L.E.D.'S. We can do this up to 6 times from this PSU and if we do the maths for our wattage usage, 3*6*6= 108watts of power as well. So now we have a led array of 6*6 L.E.D.'S ready for our tank, obviously, the bigger the power supply, the more strings you can add and the higher the voltage, the less number of drivers you will need for the same number of L.E.D.'S.

Now you are thinking perfect lets get building, 2 of these over my 4*2*2 tank and I’m cheering for about a 3rd the power usage of my 2 old 250watt MH. But think about this for a minute, if you run your L.E.D.'S at 350ma (the benchmark from which Cree base their lighting figures) you will get an output rating 100% of the specs, dial it up to 700ma and now you are getting 200% the manufacturer specs. What’s your point? Well running at 1000ma you only get 250%, so perhaps there’s a way to get more out of the same PSU.

I’m talking about dropping back from 1000ma to 700ma, this will in tern drop the forward voltage of the L.E.D.'S in each string potentially allowing you to run a 7th led on each string but also, instead of 6 amps you could run a 7th string but this time it’s 7*0.7=4.9amps. now the limiting factor on the PSU is the available wattage but 7*7*3=147 watts which just scrapes in.

So you’ve dropped the last 50% light increase but you’ve gained 13 L.E.D.'S, granted you’re using more power so the decision is ultimately yours but I hope this has given you some food for thought…

Now if all this seems like too much effort, fear not, there is such thing as a combination PSU/DRIVER that you can purchase pre built for LED light applications. These can be had with output voltage as high as 48v, all you have to do is wire a string of L.E.D.'S from them as many as you can up to 48v so back to the formula 48/3.5=13.7 (round down to 13). For a large number of people, this will be the weapon of choice, so to speak.

The driver is also what can sometimes interact with an external dimmer which, depending on the product, can be as rudimentary as a potentiometer or as advanced as a lighting controller the likes of which would be at home in a disco. If this interests you, look for a dimmable driver solution that suits your needs.

Heatsink

The heat sink is an equally important part of a DIY build. Without a decent heat sink, your L.E.D.'S will quickly overheat and fail. Now I know what you're thinking, you thought L.E.D.'S didn't make any heat. Well when it comes to high power L.E.D.'S over aquariums, that idea is both true and false. In terms of heat transfer into the tank (the major downside to MH) the statement holds true as L.E.D.'S do not transfer heat through the air from the lens. On the other hand, high power L.E.D.'S make a lot of heat through the back side of the led (the junction), up to 150°C in fact. This heat has to go somewhere, which is where the heat sink comes in. There is some pretty complicated maths involved, so my recommendation is this, get the biggest, most efficient heat sink you can that fits in your available space, and if space is limited, supplement with fans.

Your heat sink can be made of pretty much any conductive metal but, as with any other heat sink, metals like copper, aluminium (sheets of silver if your loaded) are best. Your heat sink should also have fins rather than just flat sheet, the taller the fins, the more heat will be encouraged to transfer from the plate into the surrounding air.

Optics

Although not necessarily required, depending on the depth of the tank they can be a necessity. If your tank is less than 2ft deep, with the current generation of L.E.D.'S, you may opt not to use optics if all you want to keep is soft corals or are happy to put more light demanding organisms closer to the surface. One good argument for not using optics on shallow tanks is what's called the 'spotlight effect'. Lenses can cause this effect in shallow tanks unless they are very tightly packed, it creates 'light circles' on the floor of the tank.

On the other hand, if your tank is 2ft or deeper, lenses can become the make or break of a successful lighting system. This is because they focus the light being emitted from the L.E.D. into a tighter, more efficient beam. This can be very important for achieving high par figures in deep tanks, more to the point, it's what the deep tank guys use to claim the massive 400w MH beating PAR figures.

Lenses have another unique use. Integrating lenses into your build means you can design your light fitting to keep light off the glass. This is important because it can greatly reduce the amount of time spent scraping algae off the glass.

Also lenses can help you create unique lighting effects, for example, you could only place L.E.D.'S above bombies leaving the sand bed dark to create shadows and depth etc.

Gallery

Resources

  • Cutter Electronics - Cutter Electronics – normally I would not directly link to a manufacturer on a site like this but as far as I know they are the only place in oz that people tend to buy their L.E.D.'s, etc. anyway...
  • Luxeon
  • Seoul
  • Cree
  • Luxdrive

References