When selecting among the different types of LEDs for a project or branch circuit, the physical light output is only half the battle. The real challenge lies in the solid-state driver circuitry. Whether you are wiring SMD 2835 strip lights, high-output COB (Chip-on-Board) arrays, or discrete high-power Cree emitters, your circuit design hinges on three non-negotiable factors: the driver's power factor (PF > 0.9 for commercial), inrush current (often 50x to 100x steady state), and dimmer minimum load constraints (typically 10W to 25W for trailing-edge).
This guide skips the basic physics of p-n junctions and goes straight to the bench and jobsite math required to keep your LED circuits from tripping breakers, flickering, or cooking themselves inside sealed enclosures.
The Core Circuit: Efficacy, Inrush, and Power Factor
Not all LEDs are created equal, and their efficacy (lumens per watt) dictates your thermal and electrical headroom. When comparing the different types of LEDs, you must look at the system efficacy, which includes the driver losses, not just the raw emitter output.
| Light Source / LED Type | Typical Wattage | Raw Lumens | System Efficacy (lm/W) | Primary Circuit Application |
|---|---|---|---|---|
| Incandescent (Baseline) | 60W | 800 | 13 lm/W | Resistive load (PF 1.0) |
| SMD 2835 (Mid-Power) | 9W | 900 | 100 lm/W | Strip lights, downlights |
| COB (Chip-on-Board) | 30W | 3,300 | 110 lm/W | Linear fixtures, floodlights |
| High-Power (e.g., Cree XP-L) | 10W | 1,050 | 105 lm/W | Spotlights, street lighting |
Circuit Impact Math: Inrush Current
LED drivers use large input capacitors to smooth the rectified AC waveform. When you flip the switch, these empty capacitors act like a dead short. The inrush current ($I_{inrush}$) is calculated as:
Iinrush = Vpeak / RESR
On a 120V AC circuit, the peak voltage is 170V. If the driver's equivalent series resistance (ESR) and wiring resistance total 2 ohms, the inrush spikes to 85A for roughly 200 microseconds.
Here is where breakers trip. A standard 15A C-curve breaker magnetically trips at 5x to 10x its rating (75A to 150A). An 85A inrush sits right in the nuisance-trip zone. If you parallel three of these 150W drivers on a single 15A breaker, the combined inrush hits 255A, guaranteeing an instantaneous magnetic trip. The fix: Use breakers with a D-curve (10x-20x trip) where local code permits, or specify drivers with internal NTC thermistors to limit inrush.
Power Factor (PF) and Neutral Harmonics
Apparent Power ($S$) = Real Power ($P$) / PF. A 100W LED fixture with a cheap 0.6 PF driver draws 166VA. At 120V, that is 1.38A. A high-quality 0.95 PF driver draws 105VA, or 0.87A. On a 20A branch circuit (derated to 16A for continuous loads), you can safely run 11 of the cheap drivers, but 18 of the high-PF units. Furthermore, low-PF non-linear loads generate triplen harmonics that add up on the neutral conductor, potentially overheating it even if the phase conductors are well within ampacity.
Dimmer Compatibility and Minimum Load Constraints
Dimming the different types of LEDs requires matching the dimmer's switching topology to the driver's input stage. Standard incandescent dimmers use Leading-Edge (Triac) technology. Triacs require a minimum 'holding current' to stay latched on. Because LEDs draw so little current, the triac drops out mid-cycle, causing severe strobing.
For LED circuits, you must use Trailing-Edge (ELV) dimmers, which use MOSFETs or IGBTs to chop the back half of the AC sine wave. However, trailing-edge dimmers introduce a new constraint: the minimum load.
Which Dimmer/Driver for This Fixture Count?
Let's say you are installing six 9W LED downlights (54W total) in a living room. You select a popular 150W-rated trailing-edge dimmer (like the Lutron Diva DVCL-153P). The spec sheet notes a 10W minimum load. Because 54W > 10W, the circuit will function perfectly.
But what if you are wiring a single 8W LED vanity sconce? The 8W load falls below the 10W minimum. The dimmer's internal power supply will brownout, and the light will either flicker violently or fail to turn on. The fix: Install a dummy load resistor or a bypass capacitor (like the Lutron LUT-MLC) in parallel with the fixture to artificially raise the current draw above the dimmer's minimum threshold.
Thermal Management and Enclosure Constraints
A common misconception is that LEDs don't produce heat. While the beam itself carries no infrared radiation, the p-n junction generates significant conductive heat. For every 10°C the junction temperature ($T_j$) rises above the 25°C testing baseline, lumen output degrades by roughly 5% to 8%, and the lifespan halves.
Heat Sinking and MCPCBs
High-power and COB LEDs must be mounted to a Metal Core Printed Circuit Board (MCPCB), typically aluminum with a thin dielectric layer. Standard FR4 fiberglass PCBs act as thermal insulators and will cook the emitters. For DIY or prototype builds, use a thermal interface material (TIM) like a Bergquist Gap Pad (with a thermal conductivity of at least 1.5 W/m-K) between the MCPCB and your aluminum extrusion heat sink.
Enclosure Constraints and IP Ratings
When installing the different types of LEDs in sealed enclosures (like IP65-rated outdoor bulkheads or insulated ceiling cans), ambient temperature derating is critical. A driver rated for 50,000 hours at 25°C ambient may fail in 15,000 hours if trapped in a sealed can where ambient reaches 55°C. Always check the driver's $T_c$ (case temperature) maximum rating. If the enclosure cannot dissipate heat, you must downsize the LED wattage by 20-30% to compensate for the trapped thermal energy.
Frequently Asked Questions
What are the different types of LEDs used in home wiring?
In residential wiring, you will primarily encounter three types. SMD (Surface Mount Device) LEDs, like the 2835 or 5050 chips, are used in flexible strip lights and standard A19 bulbs. COB (Chip-on-Board) LEDs pack hundreds of micro-chips into a single phosphor matrix, creating a seamless, dot-free line of light ideal for under-cabinet linear fixtures. High-Power discrete LEDs (1W to 3W each) are typically found in recessed downlights and outdoor floodlights, requiring heavy localized heat sinking.
Why do different types of LEDs flicker on dimmers and how do I fix it?
Flicker usually stems from three causes: using a leading-edge dimmer instead of trailing-edge, falling below the dimmer's minimum load requirement, or incompatible PWM frequencies in the driver. If the light flickers at the low end of the dimmer travel, it is a minimum load issue; add a bypass capacitor across the load. If it flickers randomly across the whole range, replace the switch with a dedicated ELV trailing-edge dimmer. For 'ghosting' (glowing faintly when switched off), the issue is capacitive coupling in long wire runs; install a bleed resistor across the live and neutral at the fixture.
How do I calculate the right driver for multiple LED fixtures?
It depends on whether your circuit is Constant Voltage (CV) or Constant Current (CC). For 12V/24V CV strip lights, sum the wattage of all strips and add a 20% safety margin. (e.g., 5 meters of 14.4W/m strip = 72W. 72W x 1.2 = 86.4W. Use a 100W 24V CV driver). For CC circuits (common in commercial downlights), the current (e.g., 350mA or 700mA) must match exactly, and you wire the LEDs in series. The driver's voltage range must encompass the total forward voltage ($V_f$) of the series string. If three COBs have a $V_f$ of 36V each, you need a 350mA CC driver with an output range that covers at least 108V DC.
Can I use standard incandescent dimmers with different types of LEDs?
Technically, some high-wattage LED bulbs with built-in active bleeding circuits will function on older incandescent dimmers. However, this is highly discouraged. The triac in an incandescent dimmer chops the front of the sine wave, creating massive voltage spikes that stress the LED driver's input rectifiers. This drastically shortens the lifespan of the bulb and can cause audible buzzing from the driver's inductors. Always upgrade to an ELV/Trailing-Edge dimmer rated specifically for LED loads.
