All About Smartphone Dual LED Flashes

All About Smartphone Dual LED Flashes

Greetings dear MIUI fans,

Welcome to yet another MIUI Device Classroom lesson. It's been a while since our previous classroom thread by me, which told you about Smartphone Dual Cameras. And now we're back with a new piece of information about another smartphone's "dual" thing for you. Let's start learning about Dual LED Flashes in your devices.

Introduction: Why do we use LEDs?

Let's first speak of what is achieved by using flash in your smartphone and what do we try to achieve with it? We live in a world of electronics. We have electronic devices for nearly anything. I am not speaking of the devices themselves, but of the sensors inside them. We have electronic radio modules, temperature and pressure sensors, light sensors, fingerprint sensors, image sensors... Wait, image sensors! We have already learnt about them in my previous lesson about dual cameras. The camera sensors are roughly also light sensors, which not only get information about light, but also transform that information into images. We call those images photographs or video-recordings. And as an image sensor needs to catch light for creating an image for photo or video, image quality totally depends on lighting.

By the time first phones started to use cameras people already knew about this fact, because first image sensors were used for producing digital cameras. Phone developers met a problem they had to solve while creating these phones. Cameras could use large flashes, but to make a phone compa ct and durable engineers had to create a small yet powerful light source to use in it. And they did that. Their choice was an energy effective light source for flash called LED (Light Emitting Diode), although the very first camera phones were using the xenon flash.

The first phone to use LED flash was Nokia N90. After its appearance back in 2005 phone manufacturers started using LED flashes for nearly every new phone model. Single LED flash, however, was giving bad image quality under low light conditions and allowed using camera under such conditions only on objects in a rather small distance. And that is the first cause of double-led flash setups to be invented - double-leds are needed to increase the light intensity to give more light to the objects. However, there is also another cause for using two leds for flashes. And it's the colour of the resulting image. But let's follow the order and learn them one after another.

In physics there is a law called "inverse square law", which can be applied to light. This law states that a specified light quantity or intensity is inversely proportional to the square of the distance from the light source to the object lit by it. You can see that in diagram:

The simplest formula for this law could look this way:

According to this law doubling the distance to an object makes it be lit with just a quarter intensity than it was before. Adding the second led to our flash we increase the distance to the lit object by 1.4 times. And it also increases the light intensity for the objects, which are placed closer.

Nokia N series and Xiaomi Mi 3 with dual led flash. Notice that leds are both white. This gives only light intensity growth, but can't do anything with color.

But the new question arises - why can't we add more leds to our flashes for further increasing the distance and light intensity? To answer it we should look at the inverse square law formula again. Not to overload your mind I can tell you that adding the third led will only lead to increasing distance to an object by 1.7 times compared to the single-led setup and 1.2 times compared to the dual led setup. However, the power consumption grows thrice compared to the single-led. So, we get more power consumption and bigger maximum distance. But we should care of both the factors. While phones are getting thinner each year their batteries go the same way. Still, the smartphones we use and their operating systems become more power-hungry, so the power-efficiency factor becomes one of the most important ones. That's why we can rarely see a phone with more than two leds for flash. However, it's not that you can't find those at all. There are, for example, phones like Lenovo Vibe Shot Z90 or Lumia 950 from Microsoft, which have triple-led flashes.

Vibeshot Z90 and Lumia 950 are using triple leds.

Sony Ericsson went the other way to improve lighting for camera phones. In 2009 they presented Sony Ericsson Satio - a camera phone with a xenon flash, which was giving good quality photos even under low light. Have a look at that flash in the image below.

Case 2: Color temperature

Yes, exactly, temperature. To understand what is color temperature we must speak of how it is measured.

Color temperature is the temperature of an ideal black-body radiator that radiates color of a comparable hue to that of the light source

Wikipedia

This definition found its use in photography, videography, electronics and display production. It is measured in Kelvin. Take a look at the diagram below to see the color temperature gradation. You can see that sunlight/daylight flash is somewhere around 5500K (slightly "blued" white).

The technology used for LED production allows us to create LEDs emitting light of different temperatures. However, while using single-led flashes phone manufacturers usually try to stick to the daylight flash temperature as it's the most common. And when you capture a photo under natural conditions (for example, making a photo of your girlfriend/boyfriend while you are hiking) objects in it look rather natural. But when you move your scene indoors, which happens more often, or make a photo outdoors under the street lights the colour temperature of the environment changes. This leads you to get photos of "blue-skinned people".

Or let's get back to your girlfriend/boyfriend and imagine that you are both romantic persons. You take your beloved one to a restaurant. You come there and see that it is candle-lit. Now look at the diagram above - it says that color temperature inside that rest aurant is somewhere around 1800K (close to orange colour) . You decide to make a photo again and get... Well, this is weird, but the environment will still have 1800K colour temperature, while the person you take photo of will be lit with the flash of 5500K. It will look so unnatural.

To improve the flash color temperature to conform with the environment the photos are made in phone producers made an interesting decision. They added one more led to the flash. But they chose a warmer color for it. Most of the phones with dual led flashes use white led coupled with an amber-coloured one. While taking a shot smartphone's software measures the colour temperature of the environment. Then it counts how much power to bring to the "warm" led to make a more naturally coloured photo. After that phone launches shooting and lights up the leds. The one of a white colour goes full-power and the warmer one gets just the part of power, which is needed to make a light for natural colours. By the way, this is what causes your smartphone to sometimes leave warm led turned off while taking photo with the flash enabled. Its lighting intensity simply depends on the environment color temperature.

iPhone 6 Plus True Tone Flash

As the warm led usually doesn't get fully powered dual tone flashes don't give the same lighting intensity I mentioned in the first case.

Here, just like in previous case, we also have some exceptions. For example, dual tone flashes can use not 2 LEDs, but also more. For example, the iPhone 7 / 7 plus uses the quad led dual tone flash (in Apple dual tone flash setup is called True tone).

iPhone 7 quad led True Tone Flash

This is my favorite section!

Xiaomi has made smartphones with flashes using both of the technologies. First smartphone from Xiaomi with dual led flash was Xiaomi Mi 3 with two white leds back in 2013. However, after that Xiaomi made a rather long pause in dual led flashes usage for their devices. But in January 2015 at a launch event in Beijing, China, Xiaomi revealed Mi Note. That model gave a start to Xiaomi's good tradition of using dual tone dual led flashes in Mi smartphones series. Redmi Note series got first dual tone flash setup with the introduction of Redmi Note 3 half year later - on November 24, 2015.Now every new mid- and high-range Xiaomi smartphone comes with this type of flash, improving color temperature regulation each time with MIUI updates.

Mi Note, Redmi Note 3, Redmi Pro and Mi5S accordingly

And one more thing .

Now selfies are so popular everywhere, that mentioning selfie flashes it totally a must. And as we are MIUI fans the best thing for selfie flash, which comes to my mind is Xiaomi's Mi IdeeBank Selfie LED Lamp. It combines nine warm-coloured LEDs in a comfortable form-factor and can be attached through 3.5mm jack socket to your favorite smartphone. This allows you to make selfies of a superb quality and with natural colours. You can read about it in the thread by @mitch002: [MIUI DEVICE TEAM] MI IDEEBANK SELFIE LED LAMP. Here is how it looks like and what it gives to your images.

Mi IdeeBank Selfie LED Lamp

Comparison of the photos taken without and with IdeeBank

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Credits:Thanks to @marcus_keong, @BharatG, @Candicesu and all my team for their help, motivation and suggestions.

Sources:GiffGaff Comunity, DigitalTrends, Wikipedia, Quora, Gadget House, PetaPixel, KnowYourMobile and many others

I hope I managed to tell you something new.

Source: All About Smartphone Dual LED Flashes