Which Bulb Uses Less Energy: 100W Undimmed or 200W Dimmed?
When considering the energy consumption of light bulbs, especially those that are dimmable, it's crucial to understand the full impact of dimming on their power usage. This article explores the energy efficiency of a 100-watt incandescent bulb versus a 200-watt incandescent bulb that is dimmed to match the brightness of the former.
The Energy Consumption of Different Bulbs
To determine which bulb uses less energy, we must first understand their power consumption and how dimming affects the energy use.
1. 100-Watt Undimmed Bulb
The 100-watt undimmed incandescent bulb operates continuously at 100 watts.
2. 200-Watt Dimmable Bulb
A 200-watt incandescent bulb can be dimmed to different levels. When dimmed to the same brightness as a 100-watt bulb, the actual power consumption can vary significantly based on the specific dimmer and the bulb's characteristics. Typically, a dimmed incandescent bulb consumes about 50-75% of its full wattage when dimmed to a lower brightness level.
Comparison of Energy Consumption
Let's compare the energy consumption of the two bulbs when the 200-watt bulb is dimmed to match the brightness of the 100-watt bulb.
1. Operational Assumption: If the 200-watt bulb operates at around 75% of its rated wattage when dimmed, it would consume approximately 150 watts, which is 75% of 200 watts.
2. Efficiency Consideration: Even if the 200-watt bulb operates more efficiently at a lower setting, it is still likely to consume more than 100 watts when dimmed to match the 100-watt bulb's brightness.
Conclusion
Based on these considerations, the 100-watt undimmed incandescent bulb will generally use less energy than the 200-watt incandescent bulb dimmed to the same brightness. This conclusion is supported by the higher efficiency of the 100-watt bulb, which operates at a higher filament temperature, generating more visible light relative to infrared and heat.
Dimming and Spectrum Change
The 200-watt dimmed bulb also experiences a shift in its spectrum, particularly pronounced in the infrared (IR) region. Human eye sensitivity peaks in the yellow/green spectrum, meaning that the 200-watt lamp requires more power to reach the same brightness perceived by the human eye compared to the undimmed 100-watt bulb. This is under the assumption that both lamps use the same technique and had the same spectrum when undimmed.
In addition to spectrum changes, dimming a 200-watt lamp to the same brightness as an undimmed 100-watt lamp makes it less efficient, as it produces light with reduced short wavelengths and a redder appearance.
Takeaway: Efficiency and Cost
It's important to note that while dimming a 200-watt incandescent bulb may appear to make it more efficient, the overall energy consumption remains higher than that of a 100-watt undimmed bulb. This is because the power wasted by the dimmer and the inefficiencies in the dimming process cannot be ignored.