Skip to Content

What do incandescent lights look like?

Incandescent lights have been a mainstay of indoor and outdoor lighting for over a century. Their iconic glow is familiar in homes and buildings across the world. But what exactly makes incandescent bulbs give off that distinctive warm light? In this in-depth guide, we’ll explore the anatomy of incandescent lights, how they work, and what makes their light so unique.

The Anatomy of an Incandescent Bulb

Incandescent bulbs have a simple but clever design. At their heart is a tungsten filament inside a glass bulb filled with inert gas. When electricity passes through the filament, it heats up and starts to glow white-hot. This glowing filament produces visible light that shines through the clear glass bulb. Let’s look at the key components that make up a typical incandescent light:

  • Glass bulb – The outer bulb is made of thin, transparent glass that allows the light to shine through clearly. Glass is used because it can withstand the high temperatures required to heat the tungsten filament.
  • Tungsten filament – The filament is made of a thin wire coil of tungsten metal. Tungsten is used because it has a very high melting point, allowing it to glow white-hot without melting.
  • Inert gas – The bulb is filled with a non-reactive gas like argon or nitrogen. This gas insulates the hot filament from oxidizing and extends the life of the bulb.
  • Base – The base anchors the bulb to the lamp socket and provides electrical contacts. Common base types are E26/E27 medium screw-in and bayonet (B22).
  • Support wires – Thin wires help support the filament and keep it centered inside the bulb.

When electricity flows into the base and through the tungsten filament, it heats up the filament to incandescence, causing it to glow brightly. This glowing filament becomes the light source for the bulb.

How Do Incandescent Lights Produce Light?

Incandescent lights produce light through a phenomenon known as incandescence. Here’s how it works:

  1. Electric current flows into the bulb’s base and through the tungsten filament.
  2. As the current passes through the filament, the tungsten’s resistance causes it to heat up rapidly.
  3. The filament’s temperature rises until it reaches incandescence, glowing white-hot at around 2500°C.
  4. The hot filament emits a continuous spectrum of visible light, creating the characteristic glow.
  5. The glass bulb encloses the glowing filament and allows the visible light to shine through.
  6. The inert gas prevents the hot filament from oxidizing and burning out prematurely.

This sequence happens instantly when the lamp is switched on. The electricity causes the tungsten filament to heat up and start emitting light within milliseconds.

Characteristics of Incandescent Light

The light emitted from an incandescent bulb has some unique characteristics that distinguish it from other light sources like LEDs and fluorescents.

Warm color temperature

Incandescent lights emit warm light in the 2700K to 3300K color temperature range. This gives the light a soft, golden/yellowish tone that many people find pleasing and natural.

Continuous spectrum

The glowing filament produces a continuous spectrum of light, from infrared to visible light. This full spectrum light is perceived as very natural by our eyes.

Omnidirectional light

Unlike LEDs, incandescent bulbs emit light in all directions, filling a space with soft uniform light.


Incandescent lamps can be easily dimmed by reducing the electrical power. This allows for adjustable light levels.

Slow start-up

It takes a few seconds for an incandescent bulb to reach full brightness when turned on. The filament needs to heat up first before maximum light output is achieved.

Short lifespan

The typical lifespan of an incandescent bulb is only around 1000 hours. The constant heating and cooling of the filament causes it to degrade over time, eventually leading to bulb failure.

Incandescent Wattages and Shapes

Incandescent bulbs come in a range of wattages and physical shapes to suit different lighting needs.


The most common wattages for general household lighting are:

Wattage Light Output (lumens)
25W 200-300 lm
40W 450-600 lm
60W 700-900 lm
75W 1000-1250 lm
100W 1650-1700 lm

Higher wattages produce more light output. Bulb brightness is determined by the wattage and efficacy (lumens per watt).


Different bulb shapes have been developed for specialized uses:

Shape Common Uses
A-shape (General service) Household lamps, flashlight bulbs
Bullet shape (Reflector) Spotlights, floodlights
Globe shape General and decorative lighting
Flame shape Chandeliers, wall sconces

The common A-shape bulb provides omnidirectional light well-suited for lighting homes. Other shapes help direct or focus the light in specific applications.

Types of Incandescent Bulbs

There are a few specialty types of incandescent bulbs designed for specific lighting performance:

Tungsten Halogen

Tungsten halogen bulbs contain halogen gas mixed with the inert gas inside the bulb. This allows the filament to burn hotter and brighter while prolonging lifespan and maintaining color stability.


Reflector bulbs have a faceted inner coating that reflects light in one direction. This creates a focused, intense beam of light.


Capsule bulbs have a cylindrical glass enclosure around the filament. This helps concentrate and direct the light.


Specialty shapes like flame bulbs and colored bulbs are used for decorative lighting. The non-standard shapes emit accent lighting.

Incandescent vs. LED

LED lighting has surpassed incandescent in many ways and is rapidly replacing incandescents. Here is a comparison between the two technologies:

Incandescent LED
Efficacy (lumens/watt) 10-18 70-100
Lifespan (hours) 1000 25,000-50,000
Color Temperature Warm white Warm to cool white
CRI 100 80-90+
Dimmable Yes Select models
Directional Omnidirectional Directional/omnidirectional

While LEDs are now superior in most performance metrics, incandescent lights maintain benefits like familiar warm light quality and easy dimming. The two technologies will likely coexist in many lighting applications.

The Future of Incandescent Bulbs

Incandescent bulbs are becoming increasingly rare due to legislation banning low efficacy bulbs. The technology is being phased out in favor of more energy efficient LED lighting.

However, specialty incandescent bulbs remain popular for applications like ovens, refrigerators, and decorative fixtures where warm light and dimming are valued. Vintage-style incandescent bulbs are also used in restaurants, bars, and homes to evoke a nostalgic atmosphere.

While the traditional incandescent bulb will continue its decline, innovations on the technology are emerging:

  • Halogen infrared reflecting bulbs – Advanced IR reflective coatings allow for improved efficiency.
  • Xenon-filled bulbs – Xenon gas can increase brightness and bulb life.
  • Three-way bulbs – New switches allow setting different brightnesses on one bulb.

Even with these improvements, LEDs will dominate general lighting applications for the foreseeable future. But a niche market for specialty incandescent bulbs will likely remain due to their unmatched dimming, warm light quality and vintage aesthetics.


Incandescent lights have been a trusted lighting technology for over a century. Their classic glowing filament produces a warm, inviting light that fills homes and buildings with brightness and ambiance. While now superseded in many ways by more efficient lighting like LEDs, incandescents still occupy a niche for specialty applications where a dimmable, omnidirectional warm light source is required. Their distinctive look and quality of light ensures incandescents will have a place in lighting for the foreseeable future.