Conventional Fixtures Why 575 watts?

Discussion in 'Lighting and Electrics' started by LekoBoy, Aug 13, 2008.

1. LekoBoyActive Member

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Why not 600 watts? 600 is easier to times by and four still fits on a dimmer.

2. DustincocActive Member

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4-600w lamps leave no margin for error or fluctuations in the power supply. A 575w lamp would be consuming 600w on a 120v power supply(120v*5a=600w). Since the power grid can normaly fluctuate between 110v - 120v, the voltage used to rate the lamp would be the average or 115v. (115v*5a=575w)

3. LekoBoyActive Member

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Did you learn that at collage?

4. soundlightWell-Known Member

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You never want to completely load a dimmer. That is the maximum wattage of the dimmer, not the target wattage of the dimmer. This also leaves room for slight fluctuations in voltage (as Dustincoc mentioned) as well as accounting for any power consumed from long cable runs.

Also, it's a very, very, very good idea to learn the kind of electrical theory that Dustincoc used early on, as it becomes assumed knowledge pretty fast from my experience.

Also, to give you a heads up before Derek attacks you (or wait, does he have a first time amnesty policy? can't remember...), we frown upon bad spelling.

5. JDWell-Known Member

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Which begs the question, "Why 575 watt HMI lamps?"

I have long ago give up on how they come up with some of these wattages! A simple read through a lamp supply catalog can be downright humorous!

6. lenWell-Known Member

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I learned it at decoupage, not collage.

Just designed to give you a buffer on the dimmer. Same reason you have a 1000w par can on a 1.2K dimmer channel. Or 2 x 500w pars.

And I just use 100watts per amp calculation so that I never exceed the circuit. This is more relevant when running moving lights or tree dimmers on a wall outlet in a ballroom, but the idea is the same.

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Perhaps, the answer lies in this (in)famous ETCP question, disclosed and discussed in a PLSN article by Richard Cadena:

Which of the following currents would flow in an extension cord connecting a luminaire with a 575w 115v incandescent lamp to a receptacle providing 120v?
1) 4.8 a
2) 5.0 a
3) 5.2 a
4) 6.2 a

8. JDWell-Known Member

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3
Actually, slightly in excess:
5.2173913043478260869565217391304
((575/115) / 115) *120
Give or take a little for change in filament resistance.

EDIT:
Oh, one qualifier- Just how long is this extension cord anyway?........ and what gauge is that puppy?.......

Last edited: Aug 18, 2008