How many lights can be connected to a controller, what controller do I need for RGB lights, what wiring should I use for RGB lights and/or what power supply do I need for my RGB lights?

We often get requests from customers that ask how many lights they can connect to a controller, how many lights can be connected to a controller/power supply, what type of wire they need to hook up their lights and/or controllers or what power supply they should choose - and this blog post will work to answer those questions. This article assumes you are working with RGB lights and using a DMX based, constant voltage (all HolidayCoro controllers are constant voltage) controller, though the concepts will often apply to other controller types.  If the following information looks too complicated to learn or you'd rather just "have the answer", I'd recommend against working with a DIY lighting solution because a failure to fully understand the power requirements in some parts of the system can result in damage to the hardware all the way to house fires - and I've seen them both occur - so DO NOT "wing it" here.  Alternately, you can pay someone to "run the numbers" or there are vendors that sell plug-n-play systems and while they are not as flexible as a completely DIY system, there will be little to no need to understand power requirements - just plug-n-play.

The key to understanding how many lights can be connected to a given controller, it is important to see the lights and controller as only individual parts in a system that consists of:

Lights < Lighting Wiring < Controller < Power Wiring < Power Supply

Let's work through the chain and examine each part, starting with:

• Lights
• Purpose:  The lights are the final end-goal of any lighting system and they provide the light output for your display.
• Selection:  Lights are selected on a wide variety of factors - more than can be fully described in this post but some of the factors are:
• Physical:  You'll want to select the physical format, be that modules (square, rectangle, etc), nodes (8mm/12mm usually) or strip that best suits the mounting method and directional change (going around corners, curves, etc) requirements.
• Voltage:  LED lights can come in a variety of voltages, usually 5V and 12V DC.  There are advantages and disadvantages of both of these common voltage ranges so refer to additional sources on proper voltage selection.  In general, you can go longer distances with higher voltage drops with higher voltage lights (12v) than low voltage drops (5v), though low voltage (5v) is much more power efficient and sometimes has brighter output.
• Optics:  This can include output angle (60, 90, 180, 360 degrees, etc), color mixing (5050 on-die LED, Tri-Color 8mm, three 5mm separate LEDs, etc), light diffusion and many other factors.
• Control type:  LED's can be controlled via constant current or constant voltage.  Constant current controllers are usually designed into dedicated systems like floods and it requires a specifically matched LED or LEDs to a specific controller as where constant voltage controller allows any number of LED lights as along as they are below the output requirements of the controller.  For pixel lights - the pixel is always supplied with constant voltage, even if in the chip it is constant current, so for pixels, consider them constant voltage devices.
• Lighting Wiring
• Purpose:  This wiring is either the wiring between each LED light in a string, such as in the case of RGB LED nodes or it maybe a circuit board in the case of RGB strip lights.  This wiring brings the power from the controller down to each light.
• Selection:  There are no "standards" or "normal" wiring types here - each vendors wiring can be different.  One vendor may sell RGB nodes with 24 AWG wire (thin) compared to another vendor that uses 18 AWG (thicker) wire and they can look exactly the same.  I would not always trust the data provided by the vendor, more so if your supplier is outside the US as they often lie or copy other vendor specs even if they don't match the actual product.  In an ideal world, you would want the thickest gauge wire possible as it will be able to best transport the power with the least losses but the reality is that thicker wire is harder to work with (less flexible, harder to solder to circuit boards or lights) and is more expensive, so usually there is some "balance" between cost, weight and the distance needed for the lights to be run over.
• Additional information:  Ideally, your vendor will list the maximum run on serially/continuously connected lights that can be supported before there is a "reasonable" drop in power.  So, for example, you might have one vendor that sells a 100 count string of 12v RGB nodes and they have a voltage drop from the start to the end of the string of 6v - or 50% of the power is used/lost between the start and the end.  Then you may have another vendor that has 12v RGB nodes that have a 3v drop over the 100 count string.  Again, this could be due to a number of factors - power consumption/design of each LED, gauge of the wire, quality of the circuit board, the type of solder used, the number of strands in the wire, the type of wire (100% copper, tin coated copper, tin only, etc.)  So, unless your vendor provides SPECIFIC information on how much power, over a given length at a given voltage the lights use - YOU MUST TEST AND MEASURE THEM YOURSELF!  Don't go by estimates or guesses - only trust the data.  When you've collected the power consumption amounts, you should then have a amperage (at a given voltage) or wattage for the number of lights or length of lights.  An example of this may be 37 watts per 5 meters of RGB strip.
• Additional information:  You should always measure current draw with ALL colors on, so for RGB lights this means the light will be "white" in color.  Ideally you should leave the all lights on over a period of time (an hour or so) to get a true measurement as resistance goes up (along with higher power consumption) as the wires and lights heat up.
• Controller
• Purpose:  A controller is designed to rapidly turn off and on the power going to a light to create the impression of "dimming" - it does this usually through a process called Pulse Width Modulation.  
• Selection:  Once you have selected your light type, then you've tested the power consumption, you can then determine which controller will be able to handle those lights.  Controllers are rated in amps or watts - which are the same thing when amps is combined with a given voltage.  So, if your vendor says that the controller can handle "6 amps per RGB channel" they mean that there are three individual DMX channels, each which can handle 2 amps - or a Three Channel DMX Controller.  The key here is - what is the voltage, so the voltage would be, say 12 volts, so if we use Ohms law, we come up with:  12v * 2amps = 24 watts, so this controller would handle 24 watts of power for each output or 72 watts per RGB channel (3 channels.)  So, if you've selected lights that you've TESTED to be 100 watts per "string" when they are lit up as white, than that single RGB output on the controller used in the prior example (72 watts) would not be sufficient to handle the load and you would either need to reduce the number of lights (less likely if the lights were planned correctly) or you would then need to divide up the load with either an additional controller or a multi-channel controller such as a 27 DMX channel / 9 RGB channel DMX controller.
• Additional information:  Controller terminology comes in all different forms here are some of the common terms:
• Channel:  Usually this refers to a single, two connection (wire, solder pad or screw terminal) output tied to a single DMX channel.  So a three channel controller would have three of these outputs and would also have three corresponding DMX channels.
• RGB Channel:  An RGB channel is the same thing as a three channel controller - it means that with each of the three channels, red, green and blue can be controlled to make most any color.
• DMX Channel:  This is a single output usually, that can be adjusted from a level of 0/zero/off all the way up to 255/on.
• Additional information:  It doesn't make any difference if the controller is a pixel/smart controller or dumb controller - they both use power in the same way the only difference being that one can control each light individually vs all lights at the same time.
• Power Wiring
• Purpose:  Power wiring transports the power from the power supply to the controller.
• Selection:  This selection is usually pretty easy and "by the numbers".  Those numbers are determined by the TOTAL power consumption of ALL the LEDs attached to the controller or controllers at the other end of the power cable - it has nothing to do with your controller because if you've properly allocated the maximum number of LEDs to your controller(s), than you just add them all up.  So, if you have two controllers, each with 50 watts of LEDs, you need a power cable able to handle 100 watts.  So, how do you select a cable that can handle 100 watts?  That depends on the distance to the controller.  So, these two factors - the amount of power you need to carry and the distance between the power supply and the controller(s) - we've covered this exact topic in our blog post about RGB wiring selection - check there for additional information and wiring selection charts.
• Power Supply
• Purpose:  To provide sufficient power at the correct voltage to the controller to power the lights.
• Selection:  Power supply selection is the last item to select and is pretty simple based on a few factors, such as:
• Total power consumption:  That same amount of power consumption that was determined in the power wiring section (the total power consumption of all the LEDs connected to the controller(s)) applies completely to the power supply.  If all your LEDs require 100 watts, you'll need AT LEAST a 100 watt power supply, though usually a 10 to 20% overhead is a good idea.
• Form factor:  Power supplies can be purchased in many different forms - from waterproof, to water resistant to open frame.  Mainly this has to do with how you intend to use the power supply.  If the lights are inside, a simple shrouded power supply will be fine - no need for waterproof but if you are mounting it outside in a high humidity environment, you may be better off with a waterproof power supply.  Also consider how you'll attach or mount the power supply.  Also consider air flow as high wattage (250w +) power supplies often have fans and need a sufficient volume of air for cooling.
• Voltage:  Of course the lights you selected at the start will be a given voltage and thus this applies to the power supply.  So, if you have 12v lights, you'll mostly likely need a 12v power supply.

We hope this helps you in the selection of the right wiring, power supply, controller capacity and lights for your project.  Here are some other related blog articles:

• See the effects of power consumption on the output of pixels
• How to outline your house in pixels
• Smart Pixels or Dumb RGB lights - which is right for me?