Why is the LED lighting industry abuzz with light emitting diode chips on boards (LED bBs)? What makes these the current favourite? Which applications are these good for and for which ones should these be avoided? Most importantly, what are the factors based on which you should choose the right LED COB chip? These are some questions I have tried to answer here.
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Before we get down to discussing the parameters based on which you should choose your LED chip&#;mainly COB LED&#;let me give you a perspective of the different technologies that power different type of LEDs.
DIP LEDs. Dual inline package (DIP) LED technology, as shown in Fig. 1, is likely what you think of when you picture a LED. It has been around for more than 50 years. Though it is old, DIP LEDs are far from outdated as these are still used extensively for large signs and displays.
These LEDs are typically found in electronic and electrical gadgets as indicator lights because of their low cost, high brightness and ease of install. DIP LEDs generally produce between three lumens and four lumens per LED.
SMD LED chips. SMD, or surface mounted device, chips (Fig. 2) have become very popular due to their versatility. These are much smaller in comparison to DIP. SMD LEDs have been used to create everything from light bulbs to strip lights.
SMD chips have the ability to put three diodes on the same chip. When a chip includes a red, green and blue diode, you have a chip that can create any colour you want by adjusting the level of output from each individual diode on the chip. Because these are bright and can change colours, these chips are used extensively for LED strip lights and light bulbs.
COB LEDs. COB chips have multiple diodes (more than three) on the same wafer. This is where the similarities between SMD and COB end. In fact, on every COB chip (Fig. 3) there are multiple diodes.
While SMD requires a circuit for every diode included on the chip, a COB device has only one circuit with two contacts for the entire chip, regardless of the number of diodes. This single-circuit design, regardless of the number of diodes on the chip, leads to design simplicity.
More importantly, LED COB has improved lumen-per-watt ratios in comparison to other LED technologies such as DIP and SMD. Unfortunately, the big drawback of COB (due to single-circuit design) is that multiple channels are necessary to adjust individual levels of light output to create colour-changing effects. Thus, LED COB lighting is powerful and efficient for single-colour applications, but cannot be used to create colour-changing lights.
LED COB chips vary widely in their applications and thus different chips require different wattage, voltage and produce vastly different lumen counts. However, LED COB chips have good lumens per watt ratio, starting typically from 80 lumens per watt minimum and going up to 100 lumens per watt or more. This attribute of high efficiency makes these a clear favourite for all applications running on batteries, including mobile phones, cameras and more.
MCOB LEDs. A variant of COB is now gaining popularity&#;MCOB or multiple chip on board. MCOB devices (Fig. 4) are very similar to COB chips in their application and are essentially multiple COB chips together in series. MCOB devices produce a lot of light and are even better than COBs for low-wattage applications. MCOB is a very new technology at this point that not many manufacturers are producing, but will likely catch on.
Why COB LEDs
From the above, it is clear that COBs are one of the best options available. These promise to lower the overall cost of LED luminaires by providing several benefits, such as greater design flexibility, better light distribution and simpler manufacturing process. Here is why:
1. COBs produce less heat as compared to other forms of LEDs. This, in turn, results in higher efficiency. Better thermal dissipation is achieved because the LEDs are directly mounted on an aluminium sheet, which, in turn, offers better heat dissipation as compared to other materials.
2. COBs have a lower failure rate because spot soldering is no longer required as it is built directly on to the PCB.
3. Another major factor is that, typically COBs have a much wider beam angle and thereby a higher colour rendering index (CRI). This makes these a preferred choice for outdoor lighting luminaries such as streetlights.
4. It is also possible for COB LED package to be assembled in the heat-sink directly. In such a scenario, a separate mounting and PCB are not required.
After sifting through my posts, I realized that I&#;ve neglected to write something that&#;s a little more suitable for somebody who&#;s brand spankin&#; new to the world of LED COBs. This guide will serve as a short introduction to the basic elements of COB LED lighting systems, and is a good place to start if you&#;re looking to make the switch from other types of lighting, or if you&#;re new to indoor gardening altogether.
COB LED systems are actually quite simple &#; there are only a handful of different parts, and they all go together pretty easily. The main components of a COB LED system are:
The COB LEDs themselves
Heat sinks that the COBs are mounted to
LED drivers that power the COBs
The wires that interconnect the COBs and drivers.
Not so bad, right? Let&#;s delve a little further in.
The main component of a COB LED lighting system would obviously be the lights themselves. The term COB stands for &#;Chip On Board&#;, and refers to the fact that each unit is actually several LED (Light Emitting Diode) chips mounted together on the same substrate, which is often ceramic or metal. LEDs are semiconductors that produce photons of light when electrons flow across a junction and fill &#;electron holes&#; on the other side.
COB manufacturers release data sheets for their products that dictate each unit&#;s specifications, as well as minimum, typical, and maximum values for a number of different variables. A sample of Cree&#;s data sheet for the CXB can be found here. A few examples of a COB&#;s characteristics that can be found in the data sheet include:
Color temperature (how &#;warm&#; or &#;cool&#; is the color of the light?)
Typical forward voltage (what will the voltage be across the COB at a certain level of current?)
Maximum current (how many amps of current can you drive the LED with before it dies?)
Temperature (how does the maximum current rating change, based on the temperature of the COB case?)
Luminous Flux (how bright is the light when measured at a given current and temperature?)
Relative Spectral Distribution (what wavelengths of light are most concentrated in the light produced by the COB? Does it peak in the blue range or red range?)
So, how do these little chips get mounted? Well, if there are screw holes in the board, you can screw them down, but the better alternative is always to get a holder, if possible.
If you hate soldering or don&#;t have an iron, you&#;re in luck. Many COBs have matching holders that can be used to mount the COB to the heat sink and also offer a push-in connection for wiring to the COB terminals. The holders fit over top of the COB, and screw down into the heat sink, sandwiching the COB and forcing it to press tightly against the sink. Once it&#;s in place, you can simply push wire into the holder&#;s terminals (the white plastic pieces you see on the silver holders in the picture below), which press down on the corner contact points of the COB. Nice and simple!
If you want to focus your light more, you can add reflectors that attach to the front of the COBs (this often requires a separate adapter though). You can get reflectors in different angles, colors and materials, depending on what you need to accomplish. You can also attach glass lenses or diffusers to the reflectors to protect the COBs from dirt, water, and other garden gunk.
Despite being very energy-efficient, high-powered COB LEDs do dissipate a lot of power in the form of heat. If this heat builds, it can alter the COB&#;s characteristics and subsequently damage the unit, so it must be removed somehow. The sole purpose of heat sinks in a COB light system is to pull this heat away from the COBs and keep them running as cool as possible. Heat sinks are most often made of aluminum, which is a great conductor.
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There are a number of different shapes of heat sinks, from the tested and true &#;fin&#; type, to the snazzy new &#;pin-fin&#; style. The purpose of all the fins, whether they&#;re rectangular or pins, is to increase the surface area of the heat sink as much as possible. More surface area makes it easier for heat to transfer from the COB, through the fins, and into the air.
Aside from the shape of the fins, there are 2 main types of heat sinks: active and passive.
Active heat sinks are those that use a fan to blow air over the fins to help remove the heat. If you use an actively cooled heat sink, you can get away with a much smaller unit than you could if you went passive. The risk with active cooling is that if the power supply running the fan were to ever die, the heat sink alone may not be able to cool the COB sufficiently.
Passive heat sinks are just chunks of metal and nothing else. As mentioned above, passive heat sinks must be much larger than their active counterparts in order to dissipate the same heat. What&#;s great about passive sinks is that you don&#;t have to worry about the fan dying and your COB overheating, as there are no moving parts.
If you were to try and mount your COB directly to your heat sink with nothing in between, you wouldn&#;t get very good contact between the two. When mounting to the heat sink, It&#;s imperative that 100% of the COB is making solid contact. Every minuscule pore and scratch that isn&#;t making contact is a spot that heat will build up and cause problems. For this reason, you need to use a thermal interface like a thermal pad, or thermal paste on the back of the COB to ensure the best connection possible.
LED drivers are the handy little boxes that take the power from your electrical outlet and convert it to a form that the COBs can use. The electricity coming from your outlet is alternating current (AC), and this does not work for COB LEDs &#; they require direct current (DC) instead.
LED drivers often come unterminated, which means you will have to wire an AC power plug to the end of the power cable (out of the box, it&#;s simply 3 bare wires). You will also need to terminate the positive and negative wires that connect to the COB LED circuit, as well as the 2 wires that control the dimming of the unit (some drivers come with a dimming knob built into the unit, but others simply come with 2 leads that you must attach a potentiometer to).
When purchasing an LED driver, you need to make sure that it is capable of producing enough power (in watts) to run all of your COBs. You also need to make sure it can produce this power at a certain current (in amps) and voltage (in volts). LED drivers come in 2 types: constant voltage drivers and constant current drivers. Constant voltage drivers hold their rated voltage steady and vary their current output, whereas constant current drivers hold their rated current steady, and vary their output voltage. C.V. drivers are typically used in parallel wired systems, while C.C. drivers are typically used in series wired systems.
If you&#;re new to LED, I&#;d suggest starting with constant current drivers as they are far easier to work with and are generally better-suited for most LED applications. Constant voltage drivers work wonderfully too, but can be trickier to set up and less forgiving if you mismatch the driver and COBs.
I would suggest reading these posts on selecting LED COBS and matching drivers, wiring LED COBs in series and parallel, and constant current vs. constant voltage drivers for a more detailed explanation.
This is the simplest part of the system &#; everyone has worked with wire in some capacity or another. You won&#;t need a lot of wire but you should definitely try to find the right stuff. You will need to connect all the COBs to one another and then connect the COBs back to the driver for power. See the post on wiring LED COBs in series and parallel for more information on how to hook up the COBs, and this post for help choosing wire for your system. In most cases, 18 gauge solid core cable should do the trick, but it&#;s best to check nonetheless.
Well, that&#;s it for the basics of a COB LED system! As always, you should definitely exercise caution when assembling these systems. It really helps to have some working knowledge of electricity, as there are certainly risks involved. I would suggest enlisting the help of a knowledgeable friend for the electrical stuff if it&#;s not your forte.
If you&#;re ready to get into the finer details, check out the DIY Guides section for a number of builds, articles, and calculators to help you build your own LED grow light.
If you&#;ve got a question, head on over to the forum and start a topic! Our community is happy to help, no matter what skill level you&#;re at.
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No LED Lighting Dot
COB LED strip has a smooth lightning source instead of a big bright dot that you can see in SMD strips. The light won&#;t feel sharp to your eyes since it is spread properly instead of targeting a center dot.
The hotspot on normal SMD flex stip is visible to the human eye if the light is relatively close to the surface or if the strip is visible. In contrast, COB strip gives a soft, steady light that shines from end to end and looks attractive even with no lightning dot.
The COB strips are the best for:
Places where you cannot hide the strip from view.
If the illuminated surface is within 2 feet of the light bar.
An excellent option for shining surfaces like glass/granite.
On any place where you want a neon effect.
More Flexibility
Thanks to their small size and uniform light distribution, COB strips offer more flexibility. You can easily fit them in a tight area; they won&#;t pop out as often as an SMD strip since they are light.
More stable
COB strip design uses three chips&#;one in parallel, one in each group, and one in series to form a step. Even if one or two chips stop working, the strip will continue producing light and won&#;t produce dark areas.
Wide Emitting Angle
COB LED lights have a beam angle of 180-degrees, compared with 120-degree angle of SMD LED strip lights, the area of lighting is much larger.
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