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The dual LED flash in the iPhone 5s allows changing its color from white to amber, to approximate the color temperature of ambient light. dpreview.com writes:

In fact, it features the first auto-color balancing flash of any camera. The light from a flash, LED or otherwise, is rarely the same color as the ambient light. This is particularly true when shooting in the warm tungsten light typical of indoor, nighttime scenes. With different colored light sources, white balance is almost inevitably going to be wrong for at least part of the image: the flash light may look bluish, or the ambient light may look orange.

This makes me wonder:

Is there a similar device for the hot shoe of a conventional camera?

How it could look:

  • Dual LED flash like on the iPhone, for near distance shots.

  • Or: A conventional flash with a color LCD on top. If the LCD is RGB, then the intensity of the flash would go down to one third its original intensity, approximately: red sub pixels discard green and blue photons, green sub pixels discard red and blue photons, etc.

    A compromise could be to use an LCD with just two colors. Part of the sub pixels would be yellow, allowing transmission of red, green, and yellow photons. The other sub pixels would be blue. Ideally, intensity would go down by just 50%.

    Or, as @EdgarBonet proposes below, use orange (or yellow, amber) plus white sub pixels.

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    \$\begingroup\$ The device is called CT (color temperature correction) filters. ;-) If you want to make a color LCD flash, you should choose clear colors for your subpixels, in order to retain as much light as possible. Ideally, orange and (slightly) bluish, just like the CT filters they replace. You would probably never need a strong blue CT, so use a very clear blue, or even white. \$\endgroup\$
    – Edgar Bonet
    Oct 10, 2013 at 9:12
  • \$\begingroup\$ Updated question as a flashlight is a continuous lamp used for seeing in the dark. Strobe, speedlight/lite or maybe flash bulb is the term for a hotshoe flash. \$\endgroup\$
    – AJ Henderson ♦
    Oct 10, 2013 at 17:34
  • \$\begingroup\$ @AJHenderson It depends on where you learned the Queen's English. In many parts of the English speaking world what Americans call a flashlight is referred to as a torch, and what we call a stobe or flash is called a flashlight. \$\endgroup\$
    – Michael C
    Oct 11, 2013 at 3:14
  • \$\begingroup\$ @MichaelClark - interesting, had never heard that before. Good to know, though avoiding the term flashlight is probably still preferable to avoid the obvious confusion it will cause. Thanks for educating me on that though. \$\endgroup\$
    – AJ Henderson ♦
    Oct 11, 2013 at 12:57

2 Answers 2

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I just went to B&H, drilled down to Professional Video → On Camera Lighting → On Camera Lights, then selected the "Color Temperature Control" feature, and it came up with 24 products.

Granted, this is continuous lighting intended for video, not a flashlight or a photography product, but it fits your requirements.

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  • \$\begingroup\$ Certainly these products are interesting. However, none is comparable to a flashlight. The problem is that 1. all are rather big, and 2. they are always on, blinding subjects, raising unwanted attention. \$\endgroup\$
    – feklee
    Oct 10, 2013 at 12:34
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For continuous lighting, such LED arrays exist, though your yellow two color subpixel idea wouldn't work well because LED lighting is in too narrow of a frequency band and wouldn't produce sufficient light that would get through to the sensors. LCDs won't work because they are not emitive, but blocking. You want direct emission to avoid reduction in power and uneven spread. This is actually why LEDs have to be carefully selected to work with cameras because they tend to cause color balancing issues due to their low frequency spread.

As far as a flash or strobe goes though, an "LED Flash" is a bit of an oximoron. The amount of light that can be produced by an LED is an insignificant portion of the output of an actual flash bulb. A good flash bulb will cover an area with more light than comes from the sun. I'm not sure you could even accomplish that with LEDs, no matter how many you threw at the problem. This is why color filters are used to adjust the color balance of flash output. What you could do however would be to make a color mixing filter based on the liquid filter tech used in some stage lighting, but it would likely be too bulky for general use.

Similarly, LCDs wouldn't work as they would either block too much light or not have a significant enough impact on the coloring of the light at the levels of intensity that are involved in a speedlight flash.

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  • \$\begingroup\$ The LED idea is not mine. Apple already brought it to the masses. I assume it works well with closeups. As I wrote, in the iPhone 5s there are two LEDs (dual), one yellow and one white. For longer distances, I was asking for a flash light with an LCD (≠LED) on top. Maybe one could try this with the LCD of a scrap phone. \$\endgroup\$
    – feklee
    Oct 10, 2013 at 16:56
  • \$\begingroup\$ @Feklee - I get that the idea is not yours, but I'm explaining why it won't work as a professional hotshoe product. And LED light would make more sense than an LCD. LCDs don't emit consistent light in all directions and have generally bad color properties. PVA and IPS improve on it some, but you're still losing too much power due to having to block any unused light. You would want to use an LED light and it would only be good for continuous lighting like I mentioned. The LCD also would be even dimmer than an LED display. \$\endgroup\$
    – AJ Henderson ♦
    Oct 10, 2013 at 17:21
  • \$\begingroup\$ To explain it another way, the problem with using an LCD in front of a flash bulb is that it either a) won't be able to block enough light or b) won't be able to let enough light through. LCDs work by blocking light, but you get some leakage because they can only block so much light. When you are talking about trying to block more light than direct sunlight, good luck. And if you pull it off, there will be too much light loss for what does get through, thus we're back to using a standard color filter. \$\endgroup\$
    – AJ Henderson ♦
    Oct 10, 2013 at 17:31
  • \$\begingroup\$ Thanks for your thoughts! Still, I don't fully understand your reasoning against an LCD covered flash. As I wrote: Yes, an LCD would block roughly one third of the light. In many cases, that is still enough for decent exposure. Concerning light leakage: I don't see a problem except in rare situations where ambient light is missing some colors altogether. For example if ambient light is red, then it would be problematic if the LCD covered flash also emits blue, green and white light. \$\endgroup\$
    – feklee
    Oct 11, 2013 at 9:32
  • \$\begingroup\$ @feklee - it isn't just the amount of light that the LCD blocks when transparent, it's the amount of light the LCD allows to pass when black. The reason LCDs have limited contrast ratios compared to LED backlit is that even at relatively dim levels of light, they can't effectively block the light from penetrating. If you crank up the amount of light significantly, that's going to be magnified. The combination of factors (inconsistent color temperature throughout the scene, ineffective transmission, ineffective light blocking) all combine to make it incredibly unsuitable. \$\endgroup\$
    – AJ Henderson ♦
    Oct 11, 2013 at 13:01

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