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Old March 29th, 2003, 10:53 AM   #1
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12v Dimmer for On-Camera Lighting

I was considering buying a Lowell i-Light or Bescor MPL-635 to mount atop my DVX100 for shooting wedding receptions or as an occasional offboard fill. I noticed the dimmable models were considerably more expensive (about $100 more.)

I didn't see any reason why someone couldn't just splice a potentiometer into the power cord and dump some of the power off as heat...cheap but wasteful.

A friend of mine introduced me to digital electronic circuit which achieves the same effect without wasting power as heat. It is supposed to be 98% efficient and it would conserve battery life while dimming the light at the same time. The perfect solution.

Unfortunately, nobody seems to make such a thing, so I am making one myself. They will be available to the DV lighting market on a limited basis sometime in the near future.

I am basically fishing for interest before I start dumping a bunch of money into a manufacturing process that will never pay off. If I could make an efficient dimmer available for any incandescent 12v light available for under $100US (Say $80 plus shipping) do you think there would be an interest?

Would you buy one? Any suggestions? Comments? Flames?

Thanks for your input.
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Old March 29th, 2003, 11:51 AM   #2
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They cost because they don't just dump the voltage to dim the light, the lights are actually pulsed at full power and the number of pulses are reduced from full-on down to a percentage. This keeps the color temperature of the light at near-normal.

So no, I would not be interested unless it managed the color temperature question.

Why not put your money into a reasonably cost-effective white LED light that could sit above the camera? Maybe even figure out how to parasitically power it from the camera battery.

Or a dimmable (or not) flourescent with a good color spectrum for mounting on top of the camera?
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Old March 29th, 2003, 11:58 AM   #3
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Actually, this is a PWM circuit 'pulsing' the power as you described. It would be mounted at or near the battery pack instead of on the light itself.

Although I haven't reverse-engineered one of these dimmer lights I am sure they operate on the same principle, so color temperature management would be the same. My understanding is that color temperature is essentially unaffected until power is reduced below 50%

I think this makes for a versatile solution, as it would work for any 12v incandescent light source.

Thanks for your response.
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Old March 29th, 2003, 11:06 PM   #4
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I also think they run at a high frequency to avoid flicker (which the circuit you are considering may also do).

With the lowered need for bright lights given the advancing low-light capabilities of modern cameras, I still suggest you consider, perhaps in addition to the dimmer, low-power lighting like flourescent and LED. The equivalent of 5-10 watts of halogen light would be enough for the low light level camcorders.

BTW, a consideration if you mount the control near the battery will be EMI/RFI from the cable. Some cameras, like the Sony VX2000 & PD150 are quite susceptible to these types of signals. I don't know if the pulses would effect wireless receivers.
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Old March 30th, 2003, 01:54 AM   #5
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It's already been done

Cool-Lux makes an LC7151, it's a 150 watt dimmer
and it's approx $60.

NRG makes one for around $120 (lite-rite)
http://www.nrgresearch.com/

here's a link for two articles on the subject
http://www.solorb.com/elect/solarcirc/pwm1/
http://splat.foo.is/electronics/dimmer.htm
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Old March 30th, 2003, 11:23 AM   #6
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The Cool-Lux looks like it's priced about right, but it looks to have been discontinued. All the technical information I can find online is for the AC dimmer rather than the DC dimmer. Also, I can't determine how the connectors are terminated. I'll see if I can get in touch with someone at Cool-Lux monday.

The NRG dimmer is very close to my design although a little bit larger, and I was actually planning on mounting everything inside an aluminum box, with panel-mount XLR m/f connectors at each end rather than having them on pigtails.

Thanks for the info, Bryan. I was convinced such a device simply wasn't available. I'll post some test info, photos, details once a prototype is built.
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Old March 30th, 2003, 09:30 PM   #7
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Well, there's always a bit of ND gel in front of the light that will cost you less than a penny...I've used this in a pitch-black nightclub (with a ten watt, thirty dollar light bought at Fry's)because the light was too bright for the interviewee to easily look at the camera.

If you use one of those lights that uses something similar to the FP960 Sony Infolithium, you've got hours and hours of light available in spite of it going at full blast.
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