The brightness of multi-section spiral lamps generally diminishes over time — a phenomenon known as luminous decay (light attenuation), which is part of the natural aging process of lighting equipment.
Common types of multi-section spiral lamps include spiral incandescent lamps, spiral fluorescent lamps (compact energy-saving lamps), and spiral LED lamps. The causes and rates of light decay differ across these types, as outlined below:
- Spiral Incandescent Multi-Section Lamps
The light attenuation of incandescent lamps mainly results from tungsten filament evaporation.
Their working principle is based on heating a tungsten filament to incandescence. Under prolonged high-temperature operation, tungsten atoms gradually evaporate and deposit on the inner surface of the bulb, forming a thin film that blocks light emission and reduces brightness.
Meanwhile, the filament becomes thinner due to evaporation, changing its resistance — and since lamp power depends on resistance under constant voltage, this also affects luminous output.
Although a multi-section spiral structure does not alter the fundamental mechanism of incandescent decay, improper filament design can cause localized overheating, accelerating tungsten evaporation.
Additionally, the gas convection pattern within the bulb changes with spiral geometry, affecting heat dissipation and tungsten deposition, which indirectly influences the rate of light decay.
In general, large, gas-filled spiral incandescent bulbs exhibit slower luminous decay, as the gas suppresses tungsten evaporation and the larger bulb surface enhances heat dissipation.
- Spiral Fluorescent Multi-Section Lamps (Including Compact Energy-Saving Lamps)
Fluorescent lamps emit light through ultraviolet excitation of phosphor coatings, making their light decay mechanisms more complex — and often more critical to service life than in incandescent lamps.
Phosphor degradation:
Prolonged UV exposure generates color centers and new absorption bands within the phosphor material, reducing its conversion efficiency from UV to visible light.
In spiral designs, the extended tube length and curvature can lead to uneven phosphor coating, causing localized degradation that results in uneven brightness and a perception of accelerated light decay.
Formation of absorptive films:
During long-term discharge, electrode materials sputter and deposit on the phosphor surface, forming a dark, light-absorbing film that lowers luminous output.
Because multi-section spiral lamps contain more electrodes than linear tubes, this absorptive effect tends to occur more rapidly.
Tube blackening:
Mercury ions and atoms within the lamp react and diffuse during operation, gradually causing glass darkening.
Due to the complex curvature of spiral tubes, mercury ion migration and reaction patterns vary across the lamp, increasing the risk of localized blackening, especially near electrodes or high-curvature zones, thus further contributing to luminous decay.
- Spiral LED Multi-Section Lamps
Although LED lamps generally exhibit slower light decay than traditional light sources, attenuation remains inevitable. The degree of LED light decay depends mainly on the chip quality, heat dissipation, and driver circuit stability.
Chip aging:
LEDs generate light through semiconductor recombination. Continuous current flow and heat exposure cause gradual degradation of semiconductor materials, reducing internal quantum efficiency and thus brightness.
Poor-quality LED chips decay faster, and in multi-section spiral LED lamps, brightness loss in one section is more visually noticeable.
Inadequate heat dissipation:
A significant portion of LED electrical power converts into heat. If the junction temperature rises excessively, luminous decay accelerates sharply — experimental data suggest that every 10 °C increase in junction temperature may halve the LED’s lifespan and nearly double the decay rate.
The compact internal structure of spiral LED lamps can hinder airflow and heat transfer; without proper thermal design, heat buildup between spiral sections accelerates decay.
Driver circuit aging:
Over time, electronic components such as electrolytic capacitors degrade, causing unstable current and voltage output.
Since LED brightness is closely tied to drive current, such instability can lead to overheating or premature chip failure, hastening light attenuation.
If multi-section lamps are wired in series, a fault in one segment can also affect others, resulting in complex overall light decay behavior.
Typically, high-quality spiral LED lamps exhibit less than 10% luminous decay over three years, while standard products may exceed 30% within one year.
Industry standards often define lamp lifespan as the period until luminous flux decreases to 70% of its initial value (L70).
- Mitigation and Maintenance
Light decay in multi-section spiral lamps can be mitigated by:
Selecting high-quality lamps and materials;
Ensuring optimal thermal management and environmental conditions;
Conducting regular inspections and maintenance to detect early signs of aging.
Through proper design and care, multi-section spiral lamps can maintain stable brightness output and extend operational lifespan, ensuring long-term efficiency and reliability.