Understanding Electric Lamps & Lighting Terminology

Key Lighting Terminology

Luminous Flux

The amount of light emitted by a light source, measured in lumens (lm).

Luminous Efficacy

The ratio of the luminous flux emitted (in lumens) to the power consumed (in watts). Its unit is lm/W.

Color Rendering Index (CRI)

Indicates the quality level of light sources in reproducing colors as accurately as possible.

Color Temperature (K)

Different light sources emit light at various color temperatures, measured in Kelvin (K). Here are some common examples:

• Incandescent Lamp: 2,800 K
• Fluorescent Lamp (Warm White): 3,000 K
• Fluorescent Tubes (Cool White): 4,000 K
• Fluorescent Tubes (Daylight): 6,000 K
• Direct Sunlight (Clear Sky): 6,000 K

Types of Electric Lamps

Electric lamps are categorized based on their operating principles:

Incandescent Lamps

These lamps operate by emitting light when a resistive filament is heated to high temperatures.

Components of Incandescent Lamps

• Filament: A resistive conductor, typically made of tungsten, with a melting temperature of approximately 3,400 °C.
• Bulb: The primary purpose of the bulb is to isolate the filament from the surrounding environment. If an incandescent filament were exposed to the atmosphere, the oxygen would cause it to burn immediately.

Halogen Incandescent Lamps

Very similar to traditional incandescent lamps, but constructed to significantly enhance their lifespan and luminous efficiency. In this type of lamp, a halogen gas, such as iodine, is inserted into the bulb.

Fluorescent Lamps

The primary difference between fluorescent and incandescent lamps is that fluorescents require additional equipment for operation. They use low-pressure argon gas and a small amount of liquid mercury that evaporates when the tube operates. They require a starting circuit to function.

Compact Fluorescent Lamps (CFLs)

These lamps integrate the starting equipment and have a base compatible with classic incandescent lamp sockets, making them easy to install as replacements.

Mercury Vapor Lamps

Color-Corrected Mercury Vapor Lamps

These lamps offer specific features:

• Need a starter equipment
• Yield: 40 to 60 lm/W
• Useful life: 8,000 to 16,000 hours
• Time to full brightness: 4 to 5 minutes
• CRI: 40 to 60
• Power range: 50 to 2,000 W
• Color temperature: 3,500 K to 4,500 K
• Restrike time: 3 to 6 minutes

Metal Halide Mercury Vapor Lamps

These lamps achieve higher luminous efficiency, accurate color reproduction, good color temperature, and a long lifespan.

Sodium Vapor Lamps

High-Pressure Sodium Vapor Lamps

These lamps achieve significantly increased light performance, typically ranging from 60 to 130 lm/W.

Low-Pressure Sodium Vapor Lamps

These lamps achieve very high luminous efficacy, ranging from 100 lm/W to 200 lm/W.