3 ms·

So feed them with DC current? It's not like we're talking consumer lightbulbs that need to convert AC to DC as cheaply as possible to stay competitive.

by gpm 3y ago

Scoundreller 3y ago
It’s possible, but I’m thinking a lot of constant-current devices will have some ripple in their output, even if smoothened. Human eye won’t see it, but high frame rate camera might capture at just the wrong rate to see it. It’s an surmountable problem, but can be expensive if it doesn’t need to be overcome often. (All speculation on my part)
- mrob 3y ago
  Follow your switching regulator or rectifier with some analog filtering, then a linear regulator to convert the remaining ripple to heat. It doesn't have to be very expensive, and only loses a little efficiency. I have LED light bulbs that work like this.
  - mlyle 3y ago
    > then a linear regulator to convert the remaining ripple to heat. I've become much less of a fan of the "switchilinear" approach. The control loop of a linear regulator isn't fast enough to respond to fast switching frequencies; the regulator is effectively just a resistor in a filter network at that point. Even if your switching frequency is in the regulator's loop bandwidth, the loop's gain at that frequency is almost certainly very low.
    - deleted 3y ago
      [deleted]
  - codedokode 3y ago
    Ususally they use PWM for controlling the brightness because LEDs change their spectrum with voltage change and this is undesirable. That's why PWM is used in laptop and smartphone screens.
- mlyle 3y ago
  You can filter that to be as small as you'd like. Also, it can intrinsically matter much less; if you're switching at, say, 1MHz (which can be desirable for smaller inductors), you're talking about thousands of cycles of ripple in each frame. Assuming you're using a global shutter camera: even if the ripple is completely unfiltered, the only remaining intensity effect would be that some frames get 8000 "blinks" in a frame and some get 8001. Already, stage and film lighting is a relatively small market compared to the entire lighting market, but it's not so small that NRE can't be spread across a lot of units.
- itishappy 3y ago
  Incandescent suffers the same issues if run off mains. I think the filament itself has a bit of a filtering effect (it takes time to heat and cool), but for sensitive film work I assume you'll need power conditioning either way.
  - mlyle 3y ago
    > I think the filament itself has a bit of a filtering effect (it takes time to heat and cool), I believe the time constant for most small lamps is 30ms and longer for bigger lamps. 1 / (2 * pi * 30ms) is 5Hz, so 120 Hz will be about 30 dB down. This is probably just barely big enough to matter.
    - Filligree 3y ago
      These ones, apparently, take fifteen minutes. I wonder what the filament looks like.
      - mlyle 3y ago
        Lights that take a long time to warm up are more about establishing an arc or gas temperature for full operation. They still respond to power fluctuations more quickly than the time it takes them to warm up. E.g. I have both fluorescent and HID lamps with this characteristic; they take a couple minutes to reach full brightness, but still will dim when a big load kicks on and turn off immediately when I flip the switch.
- saalweachter 3y ago
  I feel like the film industry is big enough you should be able to engineer and market a special, non-flickering, tuned spectrum LED light that produces 80-90% less heat, and as long as the TCO isn't like an order of magnitude higher, you'd have a gangbuster success.
  - KennyBlanken 3y ago
    High CRI, tunable color balance and temperature LED lights are very widespread in tv/movie/commercial shoots and have been for years...
    - codedokode 3y ago
      LED lights can be made small, flat and portable which is good for TV (e.g. for news reporting).
    - saalweachter 3y ago
      Do you happen to know if the lights everyone tells stories about -- both this news article, and other anecdotes -- are already LEDs, and still absurdly hot, because more light is better?
      - kuschku 3y ago
        The LEDs only reach up to 800W in the case of the SkyPanelX, while regular halogen lamps are still needed for more focused, higher brightness lights (which go up to 18kW per lamp(!))
        saalweachter 3y ago
        Yeah, even with the 4:1 lumen:watt advantage for LED bulbs, that's still a nearly 6x brightness advantage for halogen. Is the limiting factor the technology to make a 4500W LED bulb in the same form-factor/focus as the 18kW halogen, or does it just become prohibitively expensive to do so?

So feed them with DC current? It's not like we're talking consumer lightbulbs that need to convert AC to DC as cheaply as possible to stay competitive.

by gpm 3y ago

So feed them with DC current? It's not like we're talking consumer lightbulbs that need to convert AC to DC as cheaply as possible to stay competitive.

Scoundreller 3y ago

It’s possible, but I’m thinking a lot of constant-current devices will have some ripple in their output, even if smoothened. Human eye won’t see it, but high frame rate camera might capture at just the wrong rate to see it. It’s an surmountable problem, but can be expensive if it doesn’t need to be overcome often. (All speculation on my part)

mrob 3y ago
Follow your switching regulator or rectifier with some analog filtering, then a linear regulator to convert the remaining ripple to heat. It doesn't have to be very expensive, and only loses a little efficiency. I have LED light bulbs that work like this.
- mlyle 3y ago
  > then a linear regulator to convert the remaining ripple to heat. I've become much less of a fan of the "switchilinear" approach. The control loop of a linear regulator isn't fast enough to respond to fast switching frequencies; the regulator is effectively just a resistor in a filter network at that point. Even if your switching frequency is in the regulator's loop bandwidth, the loop's gain at that frequency is almost certainly very low.
  - deleted 3y ago
    [deleted]
- codedokode 3y ago
  Ususally they use PWM for controlling the brightness because LEDs change their spectrum with voltage change and this is undesirable. That's why PWM is used in laptop and smartphone screens.
mlyle 3y ago
You can filter that to be as small as you'd like. Also, it can intrinsically matter much less; if you're switching at, say, 1MHz (which can be desirable for smaller inductors), you're talking about thousands of cycles of ripple in each frame. Assuming you're using a global shutter camera: even if the ripple is completely unfiltered, the only remaining intensity effect would be that some frames get 8000 "blinks" in a frame and some get 8001. Already, stage and film lighting is a relatively small market compared to the entire lighting market, but it's not so small that NRE can't be spread across a lot of units.
itishappy 3y ago
Incandescent suffers the same issues if run off mains. I think the filament itself has a bit of a filtering effect (it takes time to heat and cool), but for sensitive film work I assume you'll need power conditioning either way.
- mlyle 3y ago
  > I think the filament itself has a bit of a filtering effect (it takes time to heat and cool), I believe the time constant for most small lamps is 30ms and longer for bigger lamps. 1 / (2 * pi * 30ms) is 5Hz, so 120 Hz will be about 30 dB down. This is probably just barely big enough to matter.
  - Filligree 3y ago
    These ones, apparently, take fifteen minutes. I wonder what the filament looks like.
    - mlyle 3y ago
      Lights that take a long time to warm up are more about establishing an arc or gas temperature for full operation. They still respond to power fluctuations more quickly than the time it takes them to warm up. E.g. I have both fluorescent and HID lamps with this characteristic; they take a couple minutes to reach full brightness, but still will dim when a big load kicks on and turn off immediately when I flip the switch.
saalweachter 3y ago
I feel like the film industry is big enough you should be able to engineer and market a special, non-flickering, tuned spectrum LED light that produces 80-90% less heat, and as long as the TCO isn't like an order of magnitude higher, you'd have a gangbuster success.
- KennyBlanken 3y ago
  High CRI, tunable color balance and temperature LED lights are very widespread in tv/movie/commercial shoots and have been for years...
  - codedokode 3y ago
    LED lights can be made small, flat and portable which is good for TV (e.g. for news reporting).
  - saalweachter 3y ago
    Do you happen to know if the lights everyone tells stories about -- both this news article, and other anecdotes -- are already LEDs, and still absurdly hot, because more light is better?
    - kuschku 3y ago
      The LEDs only reach up to 800W in the case of the SkyPanelX, while regular halogen lamps are still needed for more focused, higher brightness lights (which go up to 18kW per lamp(!))
      - saalweachter 3y ago
        Yeah, even with the 4:1 lumen:watt advantage for LED bulbs, that's still a nearly 6x brightness advantage for halogen. Is the limiting factor the technology to make a 4500W LED bulb in the same form-factor/focus as the 18kW halogen, or does it just become prohibitively expensive to do so?