Does a Fluorescent Bulb Use More Energy to Start Than to Run for 30 Minutes?

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Discussion Overview

The discussion centers around the energy consumption of fluorescent bulbs during startup compared to their energy usage when running for an extended period, specifically 30 minutes to 1 hour. Participants explore the mechanics of fluorescent lighting, including the role of ballasts and the nature of current used.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses skepticism about the claim that a fluorescent bulb uses more energy to start than to run for 30 minutes, indicating a lack of understanding of alternating current.
  • Another participant references the ballast's function in fluorescent bulbs, suggesting it may be relevant to the discussion.
  • A participant notes that while starting power is significantly higher, the duration of this power surge is short, leading to a lower total energy consumption.
  • There is a mention that misconceptions may arise from comparing fluorescent bulbs to high-intensity discharge (HID) lamps, which require longer heating times and higher power consumption during startup.
  • One participant provides a mathematical estimation of energy consumption, arguing that the startup energy is negligible compared to the energy used during normal operation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the claim about energy consumption during startup is a myth. There are differing views on the significance of the startup energy compared to the energy used during operation.

Contextual Notes

Some participants rely on estimations and assumptions regarding circuit capacities and power consumption, which may not account for all variables involved in fluorescent bulb operation.

Pengwuino
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Now I've heard this so much that i just have to get a complete answer to it. Since they run on AC current, i wonder "Ok maybe this myth is right because i don't have a good enough understanding about alternatig current". The idea is that a flourescent bulb (sp?) uses more energy turning on then it will take to run for 30minutes to 1 hour. I figured i could try to guesstimate the OOM with DC current figuring "ok i don't think the estimation can be THAT far off using DC principles".

When i did the math... ok yah you need a power cable capable of 'hooking up' directly to a nuclear reactor :biggrin: . So I am skeptical! I'm calling on hte experts! Does it require more energy to keep a flourescent bulb on for 30 minutes then it does to start the thing?
 
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Yah that's what I've wondered about. I had looked them up and figured there must be a large jump in current... but THAT big? Obviously not...
 
The starting power is much greater than the average one, but it lasts for only a short time, so the energy (power x time) is not great.
 
I think this misconception may have come from the fact that HID lamps need to be heated for several minutes before lighting, and that does use a significant amount of power.
 
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I don't like being next to one of our metal hailide lamps when they turn on. It kinda scares me.
 
So this is all officially a 'myth'?
 
Basic estimation will get you far. Residential circuit-breakers typically max out at 15A; at 120V this means the instantaneous power consumption of all appliances on that circuit, can never exceed 1800W. Even a 100ms (~6 cycles) startup transient at the maximum possible current, which is clearly a strong upper bound, would consume 180J; a 20W fluorescent bulb would consume as much in 9 seconds of normal use. So there you go.

The OP mentions "more energy turning on then[/color] it will take to run for 30minutes to 1 hour." In an hour, a 20W bulb consumes 72,000 Joules; it would take 40 seconds for any appliance to consume this much without tripping the breakers. This of course is grossly unresonable for a transient.
 
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