Comparing Lamp Lifespans in Working Hours

The question asks about the type of lamp that typically has the shortest working life span when measured in hours.

Let's look at the typical life spans of the lamps mentioned in the options:

• Sodium vapor lamp: Sodium vapor lamps, especially high-pressure sodium lamps used for street lighting, have a relatively long life span, often ranging from 10,000 to 24,000 working hours or even more.
• Fluorescent lamp: Fluorescent lamps, including compact fluorescent lamps (CFLs), also have a good life span. A typical fluorescent tube can last between 7,000 and 15,000 working hours. CFLs can last even longer, sometimes up to 20,000 hours.
• Mercury vapor lamp: Mercury vapor lamps are an older type of high-intensity discharge (HID) lamp. They have a decent life span, usually in the range of 10,000 to 24,000 working hours.
• Incandescent lamp: Incandescent lamps produce light by heating a filament until it glows. This method is not very efficient and causes the filament to degrade relatively quickly. Standard incandescent lamps typically have a very short life span, often only between 750 and 1,000 working hours.

Comparing the typical life spans, it is clear that the incandescent lamp has a significantly shorter life span compared to sodium vapor, fluorescent, or mercury vapor lamps.

Therefore, among the given options, the incandescent lamp has the shortest life span in working hours.

Revision Table: Typical Lamp Lifespans

Additional Information: Factors Affecting Lamp Life and Efficacy

The working life span of a lamp is an important characteristic, but not the only one. Other factors include:

• Efficacy: This measures how efficiently a lamp converts electrical power (watts) into light (lumens). It is measured in lumens per watt (lm/W). Incandescent lamps have very low efficacy (around 10-15 lm/W), while fluorescent, mercury vapor, and especially sodium vapor lamps have much higher efficacy (e.g., low-pressure sodium can exceed 150 lm/W).
• Color Rendering Index (CRI): This indicates how well a light source makes the colors of objects appear compared to natural light. Incandescent lamps have a high CRI (close to 100), while some high-efficacy lamps like low-pressure sodium have very poor CRI.
• Operating Conditions: Factors like voltage fluctuations, frequent switching (turning on and off), and operating temperature can significantly affect a lamp's actual life span.
• Failure Mechanism: Lamps fail for different reasons. Incandescent lamps typically fail when the filament breaks. Fluorescent lamps often fail when the electrodes wear out or the ballast fails. HID lamps like mercury and sodium vapor can fail due to internal component degradation or arc instability.

The short life span and low efficacy of incandescent lamps are the primary reasons they have been phased out in many places in favor of more energy-efficient alternatives like LEDs and fluorescent lamps.