What Is Pulse Width Modulation (PWM)?
Pulse Width Modulation, commonly called PWM, is a method of controlling electrical power by rapidly switching it on and off. In marine lighting, PWM is the most common technology used to dim LED fixtures without changing their color temperature or causing visible flicker.
Rather than reducing voltage to lower brightness (which can damage LEDs or cause color shift), PWM delivers full voltage in quick pulses. The ratio of "on time" to "off time" determines how bright the light appears. When the light is on 50% of the time and off 50% of the time, you perceive it as half brightness.
PWM dimming is standard in quality marine LED lights from manufacturers like Lumitec and Imtra. DRSA carries a range of PWM-compatible fixtures designed for boat cabins, helm stations, and deck lighting.
How PWM Dimming Works
PWM operates by switching power on and off thousands of times per second. The human eye can't detect these rapid cycles, so the light appears steady rather than flickering.
The key measurement is the duty cycle, expressed as a percentage:
100% duty cycle: Power is always on. Full brightness.
50% duty cycle: Power is on half the time, off half the time. Perceived as roughly half brightness.
10% duty cycle: Power is on only 10% of the time. Very dim output.
The switching happens so fast (typically 200Hz to several thousand Hz) that your eye averages the light output into smooth, continuous illumination. Quality PWM controllers run at high enough frequencies that even camera sensors won't pick up flicker.
Why PWM Is Used in Marine LED Lighting
Consistent Color Temperature
Unlike analog dimming, which reduces current and can shift LEDs toward warmer tones at low brightness, PWM maintains the same color temperature across the entire dimming range. The LED receives full power during each "on" pulse, producing the same light quality whether you're at 100% or 10%.
Efficient Power Use
PWM dimming is highly efficient because the LED is either fully on or fully off. There's minimal energy wasted as heat in the dimming circuit. On a boat where electrical capacity matters, this efficiency helps extend battery life during anchor nights or extended cruising.
Smooth Dimming Range
PWM allows fine control across a wide brightness range. You can typically dim from 100% down to 1% or lower without the light cutting out, flickering, or behaving erratically. This gives you precise control for applications like helm lighting where you need minimal light that doesn't compromise night vision.
LED Longevity
Because PWM doesn't stress the LED with reduced voltage or current variations, it tends to extend fixture life. The LED operates within its designed parameters during each pulse, reducing thermal stress and driver wear.
PWM vs. Analog Dimming
There are two main approaches to dimming LED lights:
PWM (Pulse Width Modulation)
Switches power on and off rapidly. Maintains consistent color temperature. Works well across a wide dimming range. Requires a PWM-compatible controller.
Analog (Constant Current Reduction)
Reduces the current flowing to the LED. Can cause color temperature shift at low brightness (LEDs may appear warmer). Simpler circuitry but less precise control. Some LEDs don't perform well with deep analog dimming.
Most marine-grade LED fixtures are designed for PWM dimming because it delivers better performance in the conditions boaters need: consistent light quality, reliable low-level dimming for night operation, and efficient power consumption.
PWM Frequency and Flicker
The frequency of PWM switching matters. Low-frequency PWM (under 100Hz) can cause visible flicker, especially in peripheral vision or when captured on video. Higher frequencies eliminate this problem.
Quality marine LED fixtures typically operate at 200Hz or higher. At these speeds, flicker is imperceptible to the human eye and won't show up on camera.
If you notice flickering with dimmable LED lights, the issue is usually one of these:
- Incompatible dimmer (not designed for LED or PWM)
- Low PWM frequency from a cheap controller
- Non-dimmable LED connected to a dimmer circuit
Always match your LED fixtures with compatible PWM dimmers rated for the same voltage and load.
Common PWM Applications on Boats
Cabin and Interior Lighting
PWM dimming lets you adjust cabin lights from full task brightness to a low glow for sleeping without disturbing others. The consistent color temperature means the light looks natural at any level.
Helm and Navigation Areas
Night operation requires minimal lighting that doesn't destroy dark adaptation. PWM allows you to dim helm lights to very low levels while maintaining readable instrument illumination.
Courtesy and Accent Lighting
Walkway lights, step lights, and accent lighting often use PWM to set the right mood and visibility without over-lighting the space.
Underwater Lights
Many marine underwater LED lights use PWM for color mixing (RGBW fixtures) and brightness control. PWM allows smooth transitions between colors and intensity levels.
Spreader and Deck Lights
Dimmable spreader lights use PWM to provide full brightness for nighttime deck work and lower output for general illumination during evening cruising.
PWM Controllers and Compatibility
For PWM dimming to work correctly, you need:
1. PWM-Compatible LED Fixture
The light must be designed to accept PWM input. Most quality marine LEDs support PWM, but always check the product specifications.
2. PWM Dimmer or Controller
A dimmer that outputs a PWM signal rather than simply reducing voltage. Many marine lighting systems include dedicated PWM controllers that integrate with helm switches or touchscreen panels.
3. Matched Voltage and Load Rating
The controller must handle the voltage (typically 12V or 24V DC on boats) and the total wattage of connected fixtures.
DRSA carries PWM-compatible marine LED fixtures and can help you select the right dimming solution for your installation.
Related Marine Lighting Terms
Duty Cycle: The percentage of time a PWM signal is in the "on" state during each cycle. Higher duty cycle means brighter light.
Frequency: How many on/off cycles occur per second, measured in Hertz (Hz). Higher frequency reduces visible flicker.
Analog Dimming: A dimming method that reduces current rather than switching power. Can cause color shift in LEDs.
Dimmable: A light fixture designed to work with dimming controls, whether PWM or analog.
Color Temperature: The warmth or coolness of light, measured in Kelvin. PWM dimming maintains consistent color temperature across brightness levels.
PWM Lighting FAQ
What does PWM stand for?
PWM stands for Pulse Width Modulation. It's a method of controlling power delivery by switching it on and off rapidly. The "width" of each pulse (how long it stays on) determines the average power output.
Why is PWM better than regular dimming for LEDs?
PWM maintains consistent color temperature and allows smooth dimming across a wide range. Traditional voltage-reduction dimming can cause LEDs to shift color, flicker, or fail to dim smoothly at low levels.
Can I use a standard dimmer with PWM LED lights?
It depends on the fixture. Some marine LEDs have built-in drivers that accept standard 0-10V dimming signals or trailing-edge dimmers. Others require a dedicated PWM controller. Check the product specifications for compatibility.
What PWM frequency should I look for?
For flicker-free operation, look for PWM frequencies of 200Hz or higher. Most quality marine LED fixtures operate well above this threshold.
Do all dimmable LEDs use PWM?
No. Some LEDs use analog (constant current reduction) dimming. However, PWM is the preferred method for marine applications because it offers better performance across the dimming range and maintains color consistency.