Are dimmers safe for lights?

Chris Keth · November 6, 2004

I wasthinking it would be useful to construct a number of dimmers for when I shoot. I was thinking that, in simplest terms, a light dimmer for household use, an electrical box, wire, and plug ends would do it as far as construction goes.

What I wanted to know is whether or not it is safe idea; and any considerations I should have as to wire guage, etc.

I'm confident enough with my construction skills, but not enough with my electrical knowledge.

Could something like this be used with HMIs or Tungsten, both, or neither?

Any help, advise, or construction instructions would be greatly appreciated.

Kevin Zanit · November 6, 2004

As long as you are not overloading what the dimmer is rated for (usually 1000W max) then you will be fine. Just bare in mind that there will be a color temperature shift as well as the possibility of some noise from the firmament as you dim down.

For anything bigger than 1000w you need a VariAC dimmer.

You can not use dimmer with HMIs or KinoFlos safely with resistance dimmers. Some electronic HMI ballasts have dimmers on board

Kevin Zanit

Edited November 6, 2004 by Kevin_Zanit

Chris Keth · November 7, 2004

As long as you are not overloading what the dimmer is rated for (usually 1000W max) then you will be fine. Just bare in mind that there will be a color temperature shift as well as the possibility of some noise from the firmament as you dim down.

For anything bigger than 1000w you need a VariAC dimmer.

You can not use dimmer with HMIs or KinoFlos safely with resistance dimmers. Some electronic HMI ballasts have dimmers on board

Kevin Zanit

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Which way will the color temperature change? Also, is a VariAC a "variable transformer", that alters the (I believe) voltage coming out of the box?

Nathan Milford · November 7, 2004

The more you dim the light, the more it shifts towards the red/orange.

More information on variacs can be obtained here.

Phil Rhodes · November 7, 2004

Hi,

Woah, misinformation alert. I have no qualifications in electrical engineering, but I can correct a couple of things here.

> usually 1000W

Woah, no way! Household lighting dimmers (which are fine as far as they go) are generally intended for exactly that, household situations, where 250W would be a lot. It'll be printed on the box - read the instructions. Most I've seen are 100W.

> For anything bigger than 1000w you need a VariAC dimmer.

There are bigger triac dimmrs than a kilowatt - I know there's at least 5K available commonly. Look at theatrical lighting equipment.

Variacs can be used to dim some "difficult" loads such as 12V lighting using an autotransformer - often halogen dichroics are run like this, but electronic switch-mode supplies still won't like it. You can partially dim iron-ballast fluorescents, or produce potentially interesting flicker effects, with a variac, and some more recent triac dimmers.

> Also, is a VariAC a "variable transformer", that alters the (I believe) voltage

> coming out of the box?

Yes, a variac is a variable autotransformer. Its mode of operation is, in this context, extremely different to the way a triac dimmer (most theatrical dimmers, dimmer switches for home use) work. Triac dimmers can only really be used with resistive loads unless it's specifically stated that they have the appropriate correction for dimming things like fluorescents, and even then your mileage may vary.

Discharge lamps such as HMI and MSR generally can't be dimmed at all, or at the very best you have a choice of bright, dim, or off. Even if you can dim such a lamp using a variac, it'll generally burn blue and hot and shorten the life of the lamp.

Phil

Nathan Milford · November 7, 2004

I've seen residential 1K triac dimmers (granted most are 600w and you have your little 250w inline dimmers) I've seen 2K commercial triac dimmers.

There are dimmable HMI and Flouro ballasts (obviously not based on triac technology, but sine wave inverters).

I should note that my knowledge is of U.S. power systems only though.

What misinformation? Did I miss something?

Chris Keth · November 7, 2004

I've seen residential 1K triac dimmers (granted most are 600w and you have your little 250w inline dimmers) I've seen 2K commercial triac dimmers.

There are dimmable HMI and Flouro ballasts (obviously not based on triac technology, but sine wave inverters).

I should note that my knowledge is of U.S. power systems only though.

What misinformation? Did I miss something?

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Awesome, guys. Thanks a ton! When I have a break from school I'm going to see if I can find some higher load household dimmers and wire a few up. I'm going to go on the safe side and wire with heavier wire than is needed. Thanks again, gents!