Thanks for your post. Keep us informed on the China Ball construction.

I too found the white light looks better and encodes better. Only a few times
have I used gels to warm the scene.

As others have stressed......don't use work lights, they are so dangerous.

The other reason daylight is better than tungsten is that it makes it so much easier to deal with any windows around that you can't completely block or cover with orange gel. For on-location shoots where you don't have a lot of time to set up, daylight-balanced lights can be a godsend.

I don't have the budget for HMIs or daylight-balanced Kino-Flos, but I almost always use blue gel or a dichroic filter on my tungsten lights for this very reason.

> I've so far finished a HMI China ball which is excellent,
> HUGE amount of light for very little heat. Next HMI
> project is to convert those 500W work light to HMI

Please explain how you're constructing and "converting" tungsten units to HMI.

HMI's are electronically complex instruments.

I think this is a good point- definitely a whiter light gives you less blue-channel noise.

I might note that the advantage of color-correcting filters, in the camera or on the lights, is to take advantage of the full dynamic range of Red, Green, and Blue channels on the camera all at once. Filters absorb light, so less of it gets to the camera; you reduce noise only if you color-correct with filters AND also crank up the light level to compensate for the loss. If your total light level is limited (almost always the case, in my event video work) any filter will increase noise overall.

Construction photos are here.

If you need anymore specific data please feel free to email me.

Oh and sorry about the change of user name.
I really am Rob Roy and I do live in Sydney.

Bob.

That's very interesting. I didn't know you could get off the shelf HMI parts. Perfectly good for globes and practicals, and you could probably build up the equivalent of studio spacelights (usually 6x1KW tungtsen inside a large china silk housing).

Any idea how long the run between lamp and ballast can be?

Rob Mack

Yes,
3 metres. Mostly due to the need to zap the lamp into life.

A 150W HMI is around the same light output as 800W of incandescent.

How about radio interference? Mics in particular.
might need some ferrite beads.

Thanks for sharing. Please send me more details.

3 meters isn't too shabby but you'd probably want to integrate the ballast in the fixture. For cine HMIs you can usually get 50feet or more but this is more in line with what KinoFlos can handle. Put a loop on the ballast so you can hang it on a stand.

Actually, that ballast also has the striker in it, doesn't it? If so then you want short runs anyway.

A nice home-made practical. Very cool. (No pun intended, consider it a bonus pun)

Rob Mack

RFI shouldn't be a problem, the ballasts are CE certified and once the lamp has fired it's only feeding DC to the lamp, around 80V, current limited.

The ballasts do make a very low level high frequency noise, not as bad as some of the electronic fluro ballasts though and very easy to blimp if needed.
With the ballast inside that diecast box it's very quite, you could put some rubber in there to quieten it further.

Rob Mack:
Yes the ballast includes the stricker. All you need is the ballast, lamp and socket. That's it, very simple. This system is used a lot in wall washers in shopping centers etc. Also we have a Lupo fresnel that uses the same system, pretty cheap unit as they're using ballasts sold by the thousands.

For comparison a 800W Joker Bug kit is USD 6,000, everything apart from the lamp is custom made, excellent kit but very expensive. I have found a Chinese nock off at half the price.

Bob.

"How about radio interference? Mics in particular.
might need some ferrite beads."


My basement is lit with about twenty 4-foot flor. day-light tubes and the cieling is low and white... exellent lighting and there are no problems with with rf. Every so often, though when you get to close to a ballast, the mic does pick up some 60Hz hum.... but these is easily removed with a notch filter during edit

If you're running iron ballasts with dynamic mics I could well imagine that happening. The iron ballast is the same as an electromagnet and it's generating a 60Hz magnetic field. The dynamic mic also has a coil / transformer kind of arrangement so the magnetic field from the ballast will induce a 60Hz voltage into the coil in the microphone, hence the hum.
Changing the ballasts to the more expensive electronic ones may cure the problem, I'd buy one and try it out.
Or it may create another problem, all these electronic ballasts operate at a high frequency which is audible, get a mic too close and it may pickup the sound. Different process, same sort of result. Still it help to know how the intereference is getting into things. Trying to cure RFI when it's acoustic and vice versa is a fruitless exercise.

Bob.

Most solid state HMIs I've ever worked with made noise that a boom op could hear. The instrument housing often amplifed it.

Noise was usually much, much worse in flicker-free modes and the initial solid state balasts had a switch to choose between the two. Flicker free is important if you use camera shutter settings because you could find the camera and light to be out of sync. This can result in a rythmic dimming of the light in the shot, maybe even a real flicker.

Could be old news in this day and age but you still need to be aware of the potential. Ah for the days of LTM magnetic ballasts that took two people to lift for a measily 1200w fresnel.

Rob Mack

> ...once the lamp has fired it's only feeding DC to the lamp...

If the ballast really is putting out straight DC while operating then there should be no flicker in the light output to speak of, unless the arc itself is somehow unstable and oscillating.

In mercury-halide, or fluorescent lighting for that matter, flicker is not that big an issue to start with (after they warm up). In both cases electricity is used to excite the electrons within a gas which in turn throws off enregy. AC current causes a flicker because it's actually reversing direction 60 times a second (50 in Europe)... or to put it simply... turning off and on again. This is happening as well with what ever elecrical method you use to excite the gas of your choosing (in the case of AC current), but the gas itself does not react with the speed that electricity reacts with, so you get a very large damping factor that acts lik a sponge and absorbs the 60Hz flicker that exists within the electrical excitation method.

That's NOT to say that these systems won't flicker... but if and when they do... it has more to do with a weak or old ballast as opposed to other things.

And BTW:
People seem to think that a flicker does not exist in a DC current... this is not necessarily the case at all. A PURE dc current (a chemical reaction... as in a battery) does not produce flicker. But a DC current that has been converted from ac CAN flicker just the same as the ac current itself.... it just depends on how well you smooth the current after its conversion.

Where can you buy that 150 W HMI lamp and/or parts? Is it a standard Ikea fixture? If so, what is it called (in Ikea language)?

People seem to think that a flicker does not exist in a DC current... this is not necessarily the case at all. A PURE dc current (a chemical reaction... as in a battery) does not produce flicker. But a DC current that has been converted from ac CAN flicker just the same as the ac current itself.... it just depends on how well you smooth the current after its conversion.
====================================================
A bit more complex than that these days, most DC supplies are switchmode, the incoming AC is chopped up into a high frequency and then goes through a transformer which is physically much smaller than an iron cored 50/60Hz transformer. As the ripple is at a much higher frequency less capacitance is needed for filtering.

The down side is the transformers running at that high frequency can make an audible noise.

Many things do make an acoustic noise, the head and zoom motors in cameras can get quite noisy, usually a sign they need a visit to the hospital.

Bob.

Before you go to the expense of mercury-Halide, I would experiment with fluorescent lighting first. It's not the gasses themselves in both cases that give off the colour temp... it's various other chemicals and gasses that are mixed in that causes the colour variations.

Fluorescent lighting has come a long way. People are no longer restricted to "warm-white" and "cool-white". Home lighting has become a big issue and there are all sorts of colour temps you can get... which means that you can easily change the mood of the lighting. At present, I use a 6000K colour temp in my basement (which is about as close to daylight as one can get for interior lighting). But you can get 1000, 1500, 2000, 3000... etc, and it is not that expensive... ballasts are $15 to $25

"A bit more complex than that these days,"

Sorry... no it is not.

What makes AC and DC different is the fact that AC alternates between a plus voltage and a minus. A DC current does not (for our purposes).... it only operates on the plus side (or minus side) but does not fluctuate between the 2 sides. But that does not mean that a DC current can't fluctuate between 0 and max voltage... and when converted (rectified is the actual term) it in fact DOES fluctuate. Switching power supplies are used merely because they are very good at controling and limiting the fluctuations, as opposed to the old diode-capacitor conversion process.

The bottom line... as I said, is that is that a DC current CAN and does fluctuate and it merely depends on how well the current is smoothed. The ONLY true non fluctuating DC current that exists is that which has been created by chemical reation ( a battery).

>>>Sorry... no it is not.<<<

Farss won't mention the fact, but he has a great deal of knowledge and experience in this field. So I would suggest that you put down your school physics and pay attention.

And what makes you think I don't???

BTW Serena:

I'll ask that you try hard as you can to be a little less condescending please?

If think we're getting into the area of semantics here.

One could argue that a Direct Current is one that flows in only one diraction and an Alternating Current is one that Alternates in direction. As such a simple half wave rectifier produces a DC voltage. But that's a very simplistic view!

What gives a more complete picture is to include ripple, oftenly quoted as a percentage. Even that can be a bit misleading as the frequency of the ripple can have an impact on the suitability of a DC supply for the task. That's why some high end audio gear claims better performance by not using switch mode power supplies.

Various techniques are used to 'smooth' the ripple. Also the type of rectifier and how many phases it operates from also influence the amount of filtering needed to reduce the ripple to an acceptable level. 3 phase is excellent in this respect, I've bult a few very large 3 phase DC supplies over the years, I love 3 phase!

None of this has much to do with lighting though, as I think someone pointed out, the physical aspects of the lamp can go a long way to smooth things out. Try turning a fluro out in an otherwise dark room and you'll notice the phosphors continue to glow for some time. So even the humble iron ballasted fluro doesn't turn completely off at the zero crossing point of the mains.

Now neon lights, there's a problem! Those damn neon signs in Vegas and my old PAL D8 camera, what a disaster!

Bob.