Dimmer switches are devices used to control the brightness of a light fixture by adjusting the amount of electrical current flowing to the bulb. They work by altering the voltage/current supplied to the light source, which reduces or increases the light’s intensity. From building biology perspective there are many issues one should consider when designing lighting and thinking to use dimmer switches.
There are 2 kinds of dimmer switches that are commonly used in homes:
- Pulse-Width Modulation (PWM) dimmer switches
- resistive dimmer switches
Pulse-Width Modulation (PWM) dimmer switches
PWM dimmer switches are most common in modern homes, and they work well with all kinds of light bulbs, including LED and CFL bulbs. PWM dimmers do not, however, dim the light source. They adjust the perceived brightness of the light bulb by rapidly turning it on and off. This rapid on and off switching is perceived by our eyes as more dim light, even though in reality, the light is just turned off for longer periods of time, and is always as bright when it’s turned on. While our eyes don’t pick up this rapid on and off, also called flicker, our brain has to work hard in order to process this flickering light. This causes strain on our nervous system, and can also be harmful for our eyes. You can read more about flicker in this article.
Another downside of PWM dimmers is the dirty electricity they produce. This rapid on and off switching causes disturbance to the basic AC sine wave. This disturbance is called dirty electricity. Dirty electricity is high frequency noise or transients that travel through our wiring and is emitted from wiring and electric devices. Dirty electricity is harmful both to our health, and our electric devices, so it is advisable to minimize the amount of dirty electricity in our homes & offices. You can read more about dirty electricity from this and this article.
Resistive dimmer switches
Resistive dimmer switches are a healthier option, but they don’t work well with LED or CFL bulbs. Resistive dimmers work by adjusting the amount of resistance in the switch circuit. As the resistance increases, the voltage drops. This reduces the current that reaches the light bulb, which in turn lowers the brightness of the light. When the resistance decreases, the current reaching the light bulb increases, thus creating a brighter light. Unlike PWM switches, resistive switches don’t chop or pulse the current, the amount reaching the light just increases or decreases. Therefore, resistive dimmer switches don’t create dirty electricity or flicker.
The downside of resistive dimmer switches is that the excess energy that is not used by the light, is burned off as heat. This is why it is important to design the installation so that the switch can safely cool off or ventilate the excess heat, and there are no heat sensitive materials near the switch. Another downside is that resistive dimmers are less energy-efficient as the excess energy that is not used by the light is burned off as heat.
Summary
In general, resistive dimmers are a simple, analog method of dimming light. They provide a steady, flicker and dirty electricity free source of light by adjusting resistance rather than modulating current with high-speed switching, as seen in PWM dimmers. This makes them a much better choice for healthy environments, albeit with some trade-offs in energy efficiency and heat generation.
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