I don't think LED is the answer for this one

Warning shot over the pharmacist's head?

Reply to
Jim K..
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Swapping 1000W HQI fittings for 240W LEDs.

And any chance it could mess up any filming due to strobe effects?

Reply to
ARW

Quite possibly. Philips Hue bulbs seem to be remarkably constant, and I have a desk lamp with several banks of LEDs which is fine except on the very dimmest setting when I imagine there is no overlap between one bank and another. Not that I use them for filming, but being curious, I investigated with my mobile phone, my compact camera and my SLR camera, each on video setting.

A lot depends on the shutter speed that that camera uses for each frame. Proper camcorders tend to default to the maximum exposure time (1/25 second) which gives smoother motion at the expense of blurred movement. GoPro type cameras tend to use the shortest shutter speed that the light level will allow, to give sharp frames in case you want to analyse frame by frame, but this leads to disturbing artefacts on motion - eg aircraft propellers that have disembodied blades. A short shutter speed is more likely to give venetian blind type flickering with LEDs.

Reply to
NY

I remember once shooting in a large branch of Boots and the fluorescent lights on the ceiling seemed to strobe in waves it was very weird at the time. As I gradually lost my sight I started to notice this effect with my eyes as well so it probably has to do with exposure etc. Brian

Reply to
Brian Gaff

Fluorescents, if they are nearly but not quite in phase with the camera (eg constant 25 fps camera, but mains at one extreme of the other - 49.5 or 50.5 Hz) produce weird effects because they produce two different lights: there is a blueish light with very short persistence from the gas discharge and a yellowish light with a longer persistence from the phosphor coating. Together they produce a white light (for some value of white ranging from warm white to daylight). But the strobing between the two allows you to see the blue light fading in and out which means the flicker varies in colour as well as brightness.

I saw the same effect with the blades of a desk fan, illuminated by fluorescent desk lamp - at some fan speeds there was a sharp blue image and a more blurred yellow ghost image alongside.

I'm always surprised that intermittent short-persistence lights are used for filming, because of the problem with strobing. There is a scene in the film The Krays where one of the twins is in a boxing ring at a fairground. The sequence is shown in slow motion and the flicker of the mains-frequency filming lights is very intrusive.

Reply to
NY

Isn't the HQI a discharge tube, so no temporal filtering from a phosphor? In which case they will be similar from a strobing effect.

If anything the LED might provide a more constant colour temperature over the mains 1/2 cycle.

Is 3 phase available?

Reply to
Fredxx

banks of tubes split over a three-phase supply? or with lead-lag ballasts?

Reply to
Andy Burns

Most modern pro video cameras can alter the 'shutter speed' to prevent strobing.

Reply to
Dave Plowman (News)

Using three phase mains speed florries was the way to avoid strobing with older TV cameras. Was the standard lighting rig for boxing matches.

Reply to
Dave Plowman (News)

If tubes from each phase were interspersed I can see how it would even out, but if large sections of a large shop floor were on different phases, I can see how it might annoy you out of the corner of your eye.

Reply to
Andy Burns

Strobing can occur, but less so than discharge lamps on iron ballasts.

  1. Low power LEDs often use a capacitor ballast giving 100Hz strobing. You're unlikely to be using those to get your 240w, unless it's a large array of low power things not intended for filming.
  2. Most others use electronic PSUs operating at at least 10kHz, usually far higher - those aren't a problem if the reservoir caps are big enough to ensure no 100Hz flicker, which is not consistently the case.
  3. Then there are cost cutting lights that use no reservoir cap, those flicker heavily at 100Hz.

If you do get 100Hz flicker with the 2nd type, feeding them all from a bridge rectifier & big reservoir cap will more or less eliminate it. I've no idea what the 18th has to say about 330v dc feeds though, which is what you get from such a supply. And all warranties are void. And some lamp types aren't ok with it.

NT

Reply to
tabbypurr

And I have noticed that the credits at the end of many programmes now mention someone with the job title 'colourist' or similar.

I suppose these are the people who fiddle with the colours and sometimes the effect is horrible. I am thinking of the infamous Countryfile program when they were at the feeding event of Red Kites in Wales. Someone in the post-production room made the birds have the most garishly abnormal colour imaginable.

Reply to
Andrew

Depending on the sophistication of the LED driver (and for that matter the ballast in the HQI fitting). Both could have high frequency drivers.

It will likely be a different emission spectra either way.

Reply to
John Rumm

True - and having lights on different phases close together not ideal from the H&S point of view. But H&S only applied in TV when we wanted it to. ;-)

Reply to
Dave Plowman (News)

At one time, each camera would be carefully set for best results by a trained person on site. These days, it tends to be done in post production. Just how well qualified that person is, I dunno.

But then very few domestic TVs are correctly set up anyway. Just look at a variety of makes showing the same picture in a store. They never match. And adjusting one correctly is more than plenty can do, or be bothered to do. If indeed it's possible.

Reply to
Dave Plowman (News)

Not wuite the same but I was watching TV one night and ther ewas a car driving down a road with the headlights on and they were obviously flashing I'd say at around 10Hz it was one of those high end sports cars.

Reply to
whisky-dave

LED headlights. And probably news footage. Often shot by those with little or no training.

Reply to
Dave Plowman (News)

With most dashcams, which use either 25 or 30 fps with the shortest shutter speed that the light will permit (so number plates are sharp), you see car headlights/DRLs/tail lights and traffic lights flickering due to the various refresh rates used by different LED lamps.

Reply to
NY

Yes. It's outdoors and the columns are fed from different phases, some MCBs do two columns and some columns have multiple lights on them.

Crap/dark photo here

formatting link

Reply to
ARW

Even high frequency drivers tend to have limited smoothing and give discontinuous light in keeping with the mains cycle.

You're likely right, just reminded myself that LEDs use phosphors to provide the appropriate colour temperature. Those phosphors will have differing decay times.

Reply to
Fredxx

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