COB LED Basics: A Beginner's Guide

May. 20, 2024

COB LED Basics: A Beginner's Guide

After reviewing my posts, I realized that I haven't written anything particularly suitable for someone new to LED COBs. This guide serves as a brief introduction to the basic elements of COB LED lighting systems. It's a good starting point if you're transitioning from other types of lighting or are new to indoor gardening altogether.

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COB LED systems are quite simple, consisting of only a few key parts that fit together 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 connect the COBs and drivers

Not so bad, right? Let's delve a little further in.

1. COB LEDs

The primary component of a COB LED lighting system is, of course, the lights themselves. COB stands for "Chip On Board" and refers to several LED (Light Emitting Diode) chips mounted together on the same substrate, typically 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 that specify each unit's characteristics, including minimum, typical, and maximum values for various variables. For example, Cree's data sheet for the CXB3590 provides information on:

Color temperature: How "warm" or "cool" is 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 fails?
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?

How do these chips get mounted? If there are screw holes in the board, you can screw them down, but a better alternative is to use a holder if possible.

COB Holders

If you dislike soldering or don't have an iron, you're in luck. Many COBs have matching holders that can mount the COB to the heat sink and provide a push-in connection for wiring to the COB terminals. The holders fit over the COB and screw down into the heat sink, pressing the COB tightly against it. Once in place, you can push wires into the holder's terminals, which press down on the COB's contact points. Simple and effective!

Reflectors

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. Reflectors come in various angles, colors, and materials based on your needs. You can also attach glass lenses or diffusers to protect the COBs from dirt, water, and other contaminants.

2. Heat Sinks

Despite their energy efficiency, high-powered COB LEDs dissipate a lot of power as heat. If this heat accumulates, it can alter the COB's characteristics and damage the unit. Heat sinks in a COB light system pull this heat away, keeping the COBs cool. Typically made of aluminum, heat sinks are excellent conductors.

Heat sinks come in various shapes, from the traditional "fin" type to the innovative "pin-fin" style. The fins increase the surface area of the heat sink, making it easier for heat to transfer from the COB to the air.

Heat sinks are of two main types: active and passive.

Active Heat Sinks

Active heat sinks use a fan to blow air over the fins, helping to remove the heat. With an actively cooled heat sink, you can use a smaller unit compared to passive cooling. However, the risk is that if the fan's power supply fails, the heat sink alone may not adequately cool the COB.

Passive Heat Sinks

Passive heat sinks are simply chunks of metal with no moving parts. They need to be larger than active heat sinks to dissipate the same amount of heat. The advantage is that you don't need to worry about fan failure, reducing the risk of COB overheating.

Thermal Interface

Mounting your COB directly to the heat sink without a thermal interface would result in poor contact. For optimal heat transfer, the COB must make solid contact with the heat sink. Any gaps will cause heat buildup and problems. Use a thermal pad or thermal paste on the back of the COB to ensure a secure connection.

For more information, please visit cob led vs regular led.

3. LED Drivers

LED drivers are essential components that convert power from your electrical outlet into a form usable by COBs. Electrical outlets provide alternating current (AC), but COB LEDs require direct current (DC).

LED drivers often come unterminated, meaning you'll need to wire an AC power plug to the end of the power cable. You'll also need to terminate the positive and negative wires connecting to the COB LED circuit and the wires controlling unit dimming. Some drivers have built-in dimming knobs, while others require you to attach a potentiometer.

When purchasing an LED driver, ensure it provides enough power (in watts) for all your COBs, and can deliver this power at specific current (in amps) and voltage (in volts). LED drivers are of two types: constant voltage and constant current. Constant voltage drivers hold their rated voltage steady and vary current output, while constant current drivers hold their rated current steady and vary output voltage. C.V. drivers are typically used in parallel wired systems, and C.C. drivers in series wired systems.

If you're new to LED, start with constant current drivers since they are easier to work with and generally better suited for most LED applications. Constant voltage drivers are effective but can be trickier to set up and less forgiving if you mismatch the driver and COBs.

For more details, read our posts on selecting LED COBs and matching drivers, wiring LED COBs in series and parallel, and constant current vs. constant voltage drivers.

4. Wiring

This is the simplest part of the system. You won't need much wire, but you should find the right type. You need to connect all the COBs together and then connect the COBs back to the driver for power. Refer to our post on wiring LED COBs in series and parallel for more information. In most cases, 18-gauge solid core cable will suffice, but it's best to verify.

That's it for the basics of a COB LED system! Exercise caution when assembling these systems. A basic understanding of electricity is helpful as there are risks involved. Consider enlisting the help of a knowledgeable friend for the electrical parts if it's not your strong suit.

For more detailed information, check out the DIY Guides section for builds, articles, and calculators to help you create your own LED grow light.

If you have any questions, visit the forum and start a topic! Our community is happy to assist, no matter your skill level.

COB LED Basics: A Beginner's Guide