Florescent bulbs starting energy

[Pengwuino]

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 . 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?

 

[FredGarvin]

Have you ever looked into what the ballast is for in a flourescent bulb?

Anyways, read this:
http://lightingdesignlab.com/articles/switching/switching_fluorescent.htm

 

[Pengwuino]

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...

 

[SGT]

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.

 

[russ_watters]

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.

 

[FredGarvin]

I don't like being next to one of our metal hailide lamps when they turn on. It kinda scares me.

 

[Pengwuino]

So this is all officially a 'myth'?

 

[Rach3]

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 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.