Comparing Incandescent and LED Lighting

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With climate change a central issue in President Joe Biden’s administration, designers can expect a renewed push to phase out incandescent bulbs in favor of LEDs. The latter, which utilize 70 to 80 percent less electricity than incandescents to produce the same light, are a simple, significant way to reduce carbon emissions. In fact, California is already phasing out incandescents, having started in January 2020. But what should one know about using LEDs, and how do they compare to incandescent options? Efficiency and efficacy are the qualities to keep in mind, as well as how each plays into the overall cost of the project.

Lighting Mechanisms

First and foremost is how each bulb type produces light. An incandescent comprises a wire filament encased by a glass, vacuum-sealed globe; electricity warms up the filament, generating light and heat. Incandescents run on both alternating and direct current, with no external mechanisms needed to convert the power.

Technically, an LED isn’t a bulb at all: It’s a collection of tiny, plastic-wrapped semiconductors (diodes), each of which can be as small as 2mm. Electricity passes through the diodes, releasing photons that emit light. Typically, LED bulbs mix red, green, and blue LEDs to make white light.

LEDs run on a direct, low-voltage current—the exact opposite of what U.S. power companies supply. To convert the power, LEDs use drivers, most often included in the bulb. There are notable exceptions, including LED tape, panel, and certain outdoor-rated lights, all of which require external drivers.

Efficiency

While incandescent bulbs have the lowest upfront cost of any bulb, they have the shortest lifespan, lasting about 1,000 hours each. They also have the worst energy efficiency, with 90 to 95 percent of the electricity they consume generating heat rather than producing light. Incandescents give off omnidirectional illumination: that warm, atmospheric glow actually is the light diffusing every which way—or not leaving the fixture at all. Incandescents’ source efficiency (the amount of illumination the bulb emits) hovers around 10 lumens/watt, with system efficiency (the amount of light that reaches the target area) even lower. And when an incandescent bulb stops working, it’s immediate and final.

LEDs, on the other hand, have the highest upfront cost, with bulbs priced roughly five to seven times more than incandescents. But LEDs recoup that money through operational costs and a 20,000-to-30,000-hour longevity. LEDs emit light in a specific direction, which helps them achieve impressive source and system efficiencies (the latter usually over 50 lumens/watt). LEDs stop working slowly, dimming gradually over time. Plus, because multiple LED light emitters operate with a single fixture, the loss of one or two diodes does not mean the entire bulb fails.

Efficacy

While LEDs’ efficiency is leaps and bounds ahead of any other options, their efficacy—their ability to achieve a desired effect—is still suffering growing pains.

Like incandescents, LEDs come in a wide range of sizes and light outputs. They also cycle (turn on/off) smoothly, often without flicker. They stand up to incandescents in regard to correlated color temperature, with options falling between 2200K (warm yellow/soft white) and 6500K (cool blue/daylight).

But when it comes to rendering hues, differences appear. As a whole, incandescents achieve outstanding (95-100) ratings on the Color Rendering Index (CRI), a measure of how well a bulb can reveal an object’s true colors, as if seen in natural light. LEDs rarely approach that pinnacle, with results fluctuating wildly depending on the type of light and brand of bulbs.

A further complication is that LED brands do not have consistent wattage ratings. Instead, a LED’s brightness is best judged by looking at its listed lumens. This number also can be used to figure out the most accurate swap for an incandescent equivalent.

Dimming can also prevent challenges for LEDs. Their low-voltage circuitry often means LED bulbs are incompatible with traditional dimming switches, whose power delivery is designed for the needs of incandescents. Thus, upgrading to LEDs usually means upgrading to LED dimmers. But maddeningly, not all LED bulbs work with every LED dimmer. So it requires trying out a few bulb brands or consulting the manufacturer’s list of compatible options. 

One final LED consideration is the amount of blue light the bulbs emit. While blue light in itself is not harmful, researchers have found that it can disrupt circadian rhythms and sleep. This may not be a problem for areas where it is best to stay awake, such as offices and educational facilities, but can rule out use in bedrooms and other hospitality/residential areas.

The Payoff

Cost is the final piece in the discussion. After all, while replacing one or two incandescent bulbs with LEDs doesn’t seem like it would yield much savings, it can add up. For example, using one traditional 60w incandescent for two hours every day, at a cost of 11 cents per kilowatt, would cost $4.80/year. Using the equivalent 12 watt LED for the same amount of time would be $1.00/year. Multiple that by the hundreds—or even thousands—of bulbs on a large-scale project, and the financial ramifications are significant.

Furthermore, there is that environmental impact. Lighting accounts for nearly five percent of global CO2 emissions; lighting alone can represent up to 40 percent of a building’s energy footprint. A 2020 report from the U.S Department of Energy found that if, by 2027, Americans adopted LEDs in a widespread way, the country could save more than $30 billion and 348 terawatts of electricity—the equivalent annual output of 44 large power plants. That may be incentive enough to consider the options.

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