Choosing The Right LED COB

Sani Theo

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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.

Technologies galore

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.

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Fig. 1: DIP 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 Though it is old, DIP LEDs are far from outdated as these are still used extensively for large signs and displays.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.

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Fig. 2: SMD LED chips

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.

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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.

LED COB
Fig. 3: COB LEDs

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.box77

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.

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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.

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