LEDs are appropriate for many lighting applications, they are designed to produce a lot of light from a small form factor while maintaining great efficiency. Here at LEDSupply we have a variety of LEDs for all kinds of different lighting applications. The trick is knowing how to use them. LED technology is a tad different than other lighting, and you don’t want to burn up your LEDs. This post is here to show you everything you need to know about LEDs and how to power them safely so you get the most light and the longest lifetime possible.
So What Exactly is an LED?
An LED is a type of diode that turns electrical energy into light. For those that don’t know, a diode is an electrical component that only works in one direction. So basically an LED is an electrical component that emits light when electricity flows through in one direction, from the Anode (positive side) to the Cathode (negative side). So there is the long winded answer but the name LED actually explains itself, standing for ‘Light Emitting Diode’. Basically, LEDs are like tiny light bulbs, they just require a lot less power to light up and are much more efficient in producing high light outputs.
5mm LEDs are diodes inside a 5mm diameter lens with two thin metal legs on the bottom. They are used in applications where a lower amount of light is required. For example, our brightest Cool-White 5mm LED is approximately 27 Lumens (we’ll get into what Lumens are later if you’re wondering) and our least bright Surface Mount LED is approximately 100 Lumens. 5mm LEDs also run at much lower drive currents, maxing out at around 30mA, whereas Surface Mount LEDs require a minimum of 350mA. All our 5mm LEDs are from top manufacturers and are available in a variety of colors, intensities and illumination patterns. These are great for small flashlight applications, signage and anything where you are using a breadboard as they can be used easily with their leads. Check out guide to setting up 5mm LEDs for more info on these tiny light sources.
Surface Mount LEDs (SMD)
Surface Mount LEDs are diode(s) that can be placed on a substrate (the bottom piece) with a silicon dome over the diode to protect it (see Fig. 1). We carry two different brands of high-power Surface Mount LEDs: Cree and Luxeon. In our opinion, both are excellent, that is why we carry them after all. Some people prefer one over the other but that really just comes with experience and knowing what you’re looking for. Cree tends to have higher listed Lumen outputs and are a market leader in the High-Power LED sector. Luxeon, on the other hand, has excellent colors and thermal control.
High Power LEDs can come as bare emitters (as seen in Fig. 1) or these can be mounted to a Metal Core Printed Circuit Board (MCPCB). These boards are insulated and contain conductive tracks for easy circuit connections and actually act as a small metal core heatsink. Our 1-Up and 3-Up star board designs are the most common and are approximately 20mm or 3/4” in diameter. We also offer QuadPod’s and the Luxeon K Arrays (8 & 12 LED arrays). These boards are slightly larger than the 20mm stars. (see Fig. 2) We also offer to mount all our high power LED options on a linear design in this LuxStrip.
Polarity Matters: Wiring LEDs
Electronic polarity indicates whether a circuit is symmetric or not. As we went over earlier, since LEDs are diodes, they only allow current to flow in one direction. When there is no current flow, there will be no light. Thankfully this means that if we put an LED in backwards, it won’t burn the whole system up, it just won’t come on.
The positive side of the LED is the Anode and the negative side is the Cathode. Current flows from the anode to the cathode and never in the other direction, so it is important to know how to tell your anode and cathode apart. For surface mount LEDs this is easy as the connections are labeled for you, but for 5mm LEDs you need to look for the longer lead which is the anode (positive), take a look at Figure 3 below.
One of the great things about LEDs is the different options and kinds of light you can get from them.
Correlated Color Temperature (CCT) is the process of creating different white light at different temperatures. Color temperature is specified in degrees Kelvin (K), which is a temperature scale in which zero occurs at absolute zero and each degree equals one Kelvin. The lower temperatures from 3,000K to 4,500K tend to be a warmer to neutral white whereas the higher temps 5,000K+ are the cool whites, also known as ‘daylight white’.
For colors, what really matter is the wavelength in nanometers (nm). For certain applications colors are needed just for the visual effect, but sometimes certain wavelengths are needed for applications like curing, growing, reef tank lighting, and much more. See Fig. 4 for an idea of what wavelengths and temperatures produce certain colors.
We try to carry similar color temperatures and wavelengths for each brand and type of LED. You can always find the color or wavelength of our LEDs on the sub-section of the product page and can even search by color from our LEDs dropdown menu on the homepage. In white, we carry 3000K, 4000K, 5000K and 6500K. As far as colors go, we carry from 400-660nm.
Brightness of your LED
LEDs aren’t only known for the colors, they are also a lot brighter than other light sources. Sometimes it is hard to tell how bright an LED will be because it is measured in Lumens. A Lumen is a scientific unit measuring luminous flux or the total amount of visible light from a source. Note that 5mm LEDs are usually listed in millicandelas (mcd), to switch over to lumens just note that 1,000mcd = 1 Lumen.
Why drive current matters…
The amount of light (Lumens) you can get out of an LED depends on how much current you supply to it, this is measured in milliamps (mA) or amps (A). Our high-power LEDs can take currents from 350mA to 3000mA. LEDs vary on their current ratings so be sure to keep track of this when picking an LED and driver.
Determining the Brightness
Now you’ll need to figure out how you can select the LED and driver combination that will give you the light output you need. We have done a lot of the ground work for you here in a post measuring the brightness of each of our high power LEDs at different drive currents. Take note that these are measures for 1-Up stars so if you want more light the 3-Up LEDs are a good option as they are triple the light within the same footprint.
You can always use the above resource for determining the light output you will get from your purchase, but let me just show you how to find this yourself in case you have a different LED or want a drive current that is not listed.
To do so you will need to go into the data sheet of the LED you choose. On all of our LED pages we link to the manufacturers data sheet at the bottom of the page, for this example we will use the Cree XP-L. So first you need to find the Flux Characteristics table (figure 5). We will touch on binning later which is what is labeled in the ‘Group’ column, but lets assume we are going to use a cool white XP-L that is the highest bin (v5). The highlighted number is the typical flux @ 1050mA which is what the XP-L has been tested at. To the right of that you can see typical Lumen numbers for 1500, 2000, and 3000mA drive currents.
For the sake of this example, lets say we want to run this LED with a 2100mA BuckBlock LED driver and we need to find what this would output. For in-between drive currents that aren’t listed you will then need to find the relative flux vs. current graph on the data sheet that looks like the graph to the right. So you can see from the arrow that is where the base is (at 100% relative flux). So when we go along the axis to 2100mA (?) we can see that this is a 75% increase in light. So taking the 460 lumens from above and multiplying it by 1.75 we can see that the cool white XP-L running at 2100mA would give off about 805 Lumens.
It may be hard to know what LED and lumen output you need when switching to LEDs. This is because in the past, light was always measured by the wattage of a bulb. In Figure 7 we show different incandescent bulbs and how many Lumens they give off so you can have a better idea of the light to expect or can replace your old incandescent bulbs with LEDs that have a similar Lumen output.
Viewing Angle and Optics
With our 5mm LEDs we have listed the viewing angles for each so just search for one that will work for you. As far as our surface mount LEDs go, most of them give off a very wide angle at 125 degrees! Luckily, our LED star boards are compatible and easy to use with LED optics. These secondary optics are used to focus the light, they can reflect the light from your LED into spot, medium spot, wide spot, or elliptical and oval patterns. As you can see from Figure 8, 1-Up optics are cone shaped and require an optic holder. In the case of our LED boards, optic holders have four legs that sit down into the grooves of the star. Our Triple LED stars are also compatible and built with three holes in the board for the legs of the optic to fit in.
How to Power your LEDs
LEDs are known for having the best efficacy out of all other light sources. Efficacy is the measure of how well a light source produces visible light, also described as Lumens per Watt. So in other words, how much light are we getting for our watt of power. To find this, we first will have to find out the wattage of the LED we are using. In order to find watts you need to multiply Forward Voltage (the voltage at which current starts to flow in the normal conducting direction) by drive current in Amps (note that it NEEDS to be in amps…not milliamps). Let’s take a look at the Cree XP-L 1-up LED as an example.
Say we are running this Cree XP-L at 2000mA. From Figure 8 you can see that at this drive current the forward voltage is 3.15. So to find watts we multiply 3.15 (forward voltage) by 2 A (2000mA = 2 Amps) which comes out to be 6.3 Watts.
So now to find Efficacy, we just need to divide 742 Lumens (the tested amount of Lumens for this LED at 2000mA) by 6.3 Watts. So the Efficacy (Lumens/watt) of this Cree XP-L is 117.8. This is great efficacy but also note Cree boasts that the XLamp XP-L LED has breakthrough efficacy of 200 lumens/watt running at 350mA. It is good to know that the efficacy goes down as you run more current to the LED as this increases heat which does make the LED a bit less efficient. Sometimes you will need to accept this if you need the LED to be very bright, but if you are wanting to get the best efficacy then you should run LEDs at a lower current. This is all helpful in determining how much power your applications will need as well as figuring out energy savings down the road.
A little bit more on LED drivers
This means that you need to find an LED driver that has the capability of driving LEDs at the current you need in order to get the amount of Lumens you’d like. An LED Driver is an electrical device that regulates the power to an LED or string(s) of LEDs. The driver responds to the changing needs of the LED by supplying a constant amount of power to the LED as its electrical properties change with the temperature. A good analogy in understanding this is that of a car on cruise control. As the car (LED) goes through hills and valleys (temperature changes), the cruise control (driver) makes sure it stays at a steady speed (light), regulating the gas (power) needed in doing so. The driver is so important because LEDs require very specific electrical power in order to operate properly. If the voltage supplied to the LED is lower than required, very little current runs through the junction, resulting in low light and poor performance. On the other hand, if the voltage is too great, too much current flows to the LED and it can overheat and be severely damaged or fail completely (thermal runaway). Always make sure you check the LEDs datasheet so you know what current is recommended to avoid these issues.
How much voltage do I need to light up an LED?
This is a common question asked and is actually pretty easy to figure out. All you need to know is your LED(s) forward voltage. If you have multiple LEDs in series than you need to take into account all the forward voltages combined, if you have a parallel circuit than you only need to take into account the forward voltage of how many LEDs you have per string. For more on wiring setups see here. It is a good idea to keep at least a 2 volt overhead as some drivers (like the LuxDrive drivers) require this for the driver to work properly. So if your total forward voltage for a series circuit is 9.55, you should be safe with a 12V supply. For off line drivers (AC input) just know the output voltage they are rated at and make sure you are covered, so a AC input driver with an output range of 3-12VDC would work for this application as well.
Finding wattage of your sytsem also helps you know more about the heat control you will need. Since these LEDs are high-power, they do create heat which can be very bad as you can learn here. Too much heat will make the LEDs produce less light as well as cut down on the lifetime. We always recommend using a heatsink and like to say to use about 3 square inches for every watt of LEDs. For larger wattages I would recommend looking for a heatsink that is recommended for the amount of watts you are running.
LED Binning & Quality
With the LED industry growing at a pretty rapid pace right now, it is important to understand the difference in LEDs out there. This is a common question as LEDs can range from very cheap to very expensive. I’d be careful in buying cheap LEDs as you always get what you pay for, yes the LEDs might work great at first but they usually tend not to last as long or will burn out fast because of poor testing.
All the LEDs carried here at LEDSupply are carefully selected. We only stock the best brands and color temperatures. Our vast experience in the industry has helped us learn the importance of quality manufacturing and binning of LEDs as well. In the manufacturing of LEDs, there is a variation of performance around average values in the technical data sheets. For this reason manufacturers bin the LEDs for luminous flux, color and forward voltage. We select the bins with the highest luminous flux (visible light) and lowest forward voltage, as this makes sure we have the LEDs with the best efficacy. A large amount of LED products are cheaply made and not documented correctly, which leads to many failed projects and then makes people think LEDs actually don’t last as long as they are said to. With our experience and buying power, we are able to offer the best products at reasonable prices.
This should give you a good start to understanding LEDs and what to look for, but if you have more questions or would like more info on a certain product and whether it would work for you, we are here to help. Just email us at sales@LEDSupply.com or call us at (802) 728-6031 to chat with our very knowledgeable Tech Support Team.