What are Conventional Light Sources?

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- GoPhotonics

Apr 11, 2024

Conventional light sources are light sources based on older technologies of producing light before the advent of more advanced technologies like LEDs. These traditional sources include incandescent bulbs, halogen lamps, fluorescent tubes, and compact fluorescent lamps (CFLs). They operate by converting electrical energy into light through various mechanisms such as thermal radiation, gas ionization, or fluorescence. Despite their widespread use in the past, conventional light sources are gradually being replaced by more energy-efficient, longer-lasting, and environmentally friendly alternatives like LEDs.

Different Types of Conventional Light Sources

Fluorescent Lamps:


A fluorescent lamp, also known as a fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. This electric light source relies on ultraviolet radiation emitted by mercury vapor to excite phosphor, which emits visible light. This conventional light source operates based on the principle of gas excitation. When electricity is applied to a glass tube with mercury vapor and a small quantity of inert gas, such as argon or krypton, an arc discharge is generated. This discharge excites the mercury atoms, causing them to emit ultraviolet (UV) radiation. The UV radiation subsequently interacts with a phosphor coating that lines the interior of the tube, stimulating the phosphors to emit visible light. Fluorescent lamps offer relatively high efficiency and are commonly used in commercial, residential, and industrial lighting applications due to their longevity and energy efficiency.


  • High luminous efficacy (typically 50-100 lumens per watt).
  • Longer lifespan compared to incandescent bulbs (typically 7,000 to 15,000 hours).
  • Available in various sizes and shapes for different applications.


  • Contains small amounts of mercury, requiring proper disposal.
  • Flicker and hum may occur, especially with older models.
  • Require a ballast for operation, adding complexity and cost.

Halogen Lamps:


Halogen lamps are a type of incandescent lamp with a tungsten filament sealed in a compact transparent envelope. The envelope is filled with a mixture of an inert gas and a small amount of a halogen, such as iodine or bromine. The halogen gas, in combination with the tungsten filament, initiates a halogen-cycle chemical reaction. It operates on the principle of thermal radiation, where light is generated by heating a solid material to an extremely high temperature. When the lamp is illuminated, the tungsten filament heats up due to the flow of electricity. As the filament reaches high temperatures, some of the tungsten atoms evaporate and deposit onto the inner surface of the envelope. Thus, prolonging its lifespan and preserving the clarity of the envelope.

However, unlike traditional incandescent lamps, the presence of the halogen gas prevents the tungsten from settling on the envelope's surface. Instead, the halogen gas combines with the evaporated tungsten atoms to form tungsten halide molecules. These molecules are transported back to the filament by convection currents within the lamp.

As the tungsten halide molecules reach the filament, they release tungsten atoms. These atoms undergo breakage due to the high temperatures encountered. The freed tungsten atoms then redeposit onto the filament, effectively regenerating it. This constant cycle of evaporation and redeposition allows the filament to maintain its structural integrity over multiple lighting cycles.

This mechanism enables the filament to operate at higher temperatures compared to  traditional incandescent lamps, resulting in brighter and whiter light. The brightness of the light emitted is directly related to the temperature of the heating element. The regeneration of the filament prolongs the lamp's lifespan, making halogen lamps a popular choice for various lighting applications.

The compact size of halogen lamps facilitates their integration into compact optical systems, such as projectors and illumination setups. Additionally, a smaller glass envelope may be encased within a larger outer glass bulb, which maintains a lower temperature, safeguards the inner bulb from contamination, and enhances the mechanical resemblance to conventional lamps.


  • Halogen lights emit a color temperature similar to sunlight, producing a whiter light compared to the orange hue of incandescent bulbs.
  • Longer lifespan than traditional incandescent bulbs (typically around 2,000 hours).
  • Crisp, white light with good color rendering properties.


  • Higher operating temperatures, requiring caution during handling.
  • Still relatively inefficient compared to newer lighting technologies.
  • Sensitive to skin oils, reducing lifespan if touched.

Incandescent Lamps:


The incandescent lamp, also known as a light bulb, operates as an electric light source by harnessing the phenomenon of incandescence, wherein light emission results from filament heating. These lamps are the most iconic of conventional light sources. They work by passing an electric current through a thin filament, typically made of tungsten, within a glass bulb filled with inert gas. The resistance of the filament to the current generates heat, causing it to glow and emit visible light. Incandescent lamps have a warm, inviting light but are relatively inefficient, with much of the energy being lost as heat. Despite their widespread use in residential and decorative lighting, incandescent lamps are being phased out in many regions due to their low efficiency. They come in various sizes and wattages, catering to different lighting needs. The voltage range for these bulbs typically spans from 1.5V to 300V.


  • Simple design and low manufacturing cost.
  • Instantaneous start-up time.
  • Dimmable without additional equipment.


  • Low luminous efficacy.
  • Short lifespan (typically around 1,000 hours).
  • Generates a significant amount of heat.

Mercury Vapor Lamps:

Mercury vapor lamps is a kind of gas discharge lamp that produce light through the excitation of mercury vapor within a sealed glass bulb. When electricity is applied, it creates an arc discharge within the bulb, exciting the mercury atoms. These excited atoms emit ultraviolet radiation, which then stimulates the phosphor coating on the bulb's inner surface, producing visible light. Mercury vapor lamps are known for their high-intensity light output and are commonly used in street lighting, industrial facilities, and large indoor spaces.


  • Good luminuous efficiency
  • Color rendering is better than that of high pressure sodium street lights.
  • Long lifespan (typically around 24,000 hours).


  • Require a warm-up time to reach full brightness.
  • Emit UV radiation, requiring additional shielding.
  • Mercury content poses environmental concerns.

Neon Lamps:

Neon lamps, also known as neon glow lamp, is a miniature gas-discharge lamp that utilize the unique properties of neon gas to produce light. The lamp typically consists of a small glass tube that contains a mixture of neon and other gases at a low pressure and two electrodes such as an anode and a cathode. The electrodes at each end create an electric field when a voltage is applied. This electric field ionizes the neon atoms, causing them to emit photons of light. Neon lamps emit a distinct, colorful glow and are often used for signage, decorative lighting, and indicator lights.


  • Long lifespan (up to 30,000 hours).
  • Emit light in various colors.
  • Low operating voltage.


  • Limited color options compared to other types of lighting.
  • Require a higher voltage to ignite.
  • Not suitable for general lighting due to low efficiency.

High-Intensity Discharge (HID) Lamps:

High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp that generate light through an electric arc between tungsten electrodes contained within a translucent or transparent arc tube made of fused quartz or fused alumina. HID lamps encompass a variety of light sources, including metal halide lamps and sodium vapor lamps. These lamps generate light by passing an electric current through a gas or vapor under high pressure, creating an arc discharge. This discharge produces intense light output across a broad spectrum. HID lamps are commonly used in outdoor lighting, stadium lighting, and high-ceiling applications where high levels of illumination are required.


  • High light output (typically 85 lumens per watt).
  • Long lifespan compared to incandescent bulbs (varies based on type).
  • Available in various types for different applications (e.g., metal halide, high-pressure sodium).


  • Require a warm-up time to reach full brightness.
  • Relatively high initial cost compared to some other types of lighting.
  • Some types emit UV radiation.

Comparison of Light Emission by Different Conventional Light Sources



Light (lm)

Power consumption (W)


300 nm (UV) - 1400 nm (NIR)

16 - 24 lm/W

40 W - 100 W


320nm - 1100 nm

24 lm/W

29 W - 72 W


580 nm - 650 nm

50 - 65 lm/W

400 W

Mercury Vapor

350 nm - 600 nm

35 - 55 lm/W

40 W - 1000 W

High-Intensity Discharge (HID)

400 nm - 640 nm

85 lm/W

35 W - 50 W


400 nm - 700 nm

50 - 100 lm/W

13 W - 15 W

Applications of Conventional light sources

Conventional light sources have been widely utilized in various applications across residential, commercial, industrial, and outdoor settings. Some common applications include:

  • Residential Lighting: Incandescent bulbs, halogen lamps, and fluorescent tubes have traditionally been used for general lighting in homes, illuminating living spaces, kitchens, bedrooms, and bathrooms.
  • Commercial Lighting: Conventional light sources find extensive use in commercial buildings such as offices, retail stores, restaurants, and hotels for general illumination, task lighting, and accent lighting purposes.
  • Industrial Lighting: High-intensity discharge (HID) lamps, including metal halide and sodium vapor lamps, are commonly employed in industrial facilities, warehouses, and manufacturing plants where high levels of illumination are required over large areas.
  • Street Lighting: Mercury vapor lamps, sodium vapor lamps, and metal halide lamps are often used for street lighting to provide illumination for roads, highways, and public spaces during nighttime hours.
  • Outdoor Lighting: Conventional light sources are also utilized for outdoor applications such as security lighting, landscape lighting, parking lot lighting, and stadium lighting due to their ability to produce high-intensity light over large areas.
  • Decorative Lighting: Incandescent bulbs, neon lamps, and halogen lamps are frequently used for decorative purposes in homes, hotels, restaurants, and entertainment venues to create ambiance and enhance visual appeal.
  • Specialized Applications: Conventional light sources are employed in specialized applications such as photography, stage lighting, medical lighting, and automotive lighting due to their specific characteristics such as color rendering, brightness, and beam control.