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Home / Tips and Tricks / Your smart lights do not dimmer how you think they are. Here's why

Your smart lights do not dimmer how you think they are. Here's why



  led-light-bulb.jpg

The LEDs in your smart LEDs cannot dampen the way you can expect – but there is a good reason to do so.


Tyler Lizenby / CNET

"Alexa, put the candles to 50%."

I use voice commands that way to control the bright lights in my own home all the time. It is really one of the smart benefits of smart lighting – with a single voice command or a crane in an app, you can set your lights to the exact level of brightness you want on a 100-point scale, typically with zero flicker total .

But look a little closer at how smart light bulbs actually fog, and you will notice that the 100-point scales vary from light bulb to light bulb. Some turn the brightness down linearly – 10% of the total lumen output at the 10% setting, 60% of the total lumen output at the 60% setting, and so on. Set the bulb to 50%, get half the maximum lumen. Sounds reasonable, right?

However, other lamps take a logarithmic approach, with the lumen rapidly lowering to lower than expected levels when you dial down the items. Tell Alexa to put a light bulb that way to 50%, and you can only get 25% of the lumen that you would get at full brightness. What gives?

The answer is indeed wonky, so carry me here, but it is fascinating, and it comes down to the difference between measured brightness and perceived [brightness]. And ultimately, science supports how our eyes work the logic of logarithmic dimming – but it's not a perfect approach.

So what kind of impact can the mist curve differences do in the way these lights light your home? That was what I wondered.

Read more : Best Cheap Smart Light Bulbs

This TP-Link Kasa LED rings the brightness in linear mode while the Philips Hue White LED uses a logarithmic dimming curve. [19659003] Ry Crist / CNET

Warning: Forward curves

To look at the lamp's light attenuation curves, I put each into our lighting laboratory's integration sphere and then use the built-in spectrometer to measure the brightness at all 100 dimmable settings. With several hundred readings coming through, it was a dull process, because when you dim an LED down, it uses less energy and produces less heat. This, in turn, makes the bulb a little brighter. You can see the effect in the TP link graph above the left – it takes a linear approach to dimming, but when I slowed it down to take measurements, those readings began to lift off the dotted line representing the target.

It is not a noticeable change in the naked eye, but to plot correct dimming curves in a Google sheet there was little pain. I have done my best to keep the readings as accurate as possible for these graphs, but continue and assume as much as a 10% error margin on the specific lumen counts, especially in the middle of each dimming curve. [19659000] Read more : Complete guide to Philips Hue

I started looking at several of the relatively affordable smart lights that I wrote about in my latest purchase guide here at CNET. Four of them – Philips Hue White LED Lifx Mini White, C by GE Soft White Life LED and Cree Connected LED – took a logarithmic setting to dimming. The other three – Eufy Lumos Mini LED Bedding Element Classic LED and TP-Link Kasa KB100 LED – kept things more or less linear.

An obvious difference is that the logarithmic light bulbs offer less measurable light than you would expect in the lower half of the dimming curve. I noticed the biggest difference with the Lifx Mini White LED. When set to 50%, I measured it at 151 lumens, which is only 23.4% of the lamp's maximum lumen output at the 100% setting.

In addition to logarithmic bulbs such as Philips Hue White LEDs that really flatten out at the bottom of this curve, actually do not offer much of any difference in either of the lower settings or so. In fact, the settings 1% and 10% brightness with the Hue White LED were only separated by 2 lumens.

"It's Intentional Since your eye perceives the brightness changes logarithmically," explains Philips Hue's technical manager George Yianni. big as the whole range. "

This chart from the Lighting Controls Association gives an idea of ​​what a linear approach to dimming actually looks like perceived brightness (the blue line). In summary, the light attenuates too slowly in the upper half of it dimmable area and too fast in the lower half of the dimmable area.

Lighting Controls Association

And that is the core point of the argument, a light bulb using a linear dimming curve will not offer much of a change in perceived brightness in the upper half of this dimmable area because it is not lowered In other words, the settings above 50% or all will look very similar.

The logarithmic setting makes you notice a change in perceived brightness directly when you call things. Basically, you want a light bulb's measured brightness to fall quickly when you call down the upper half of its dimmable area, then more gradually in the bottom half.

Lifx explained its own logarithmic dimming curve in a similar way. "We are more sensitive to changes in dim light sources than light sources," says Lifx spokesman Charlie Felton. "Basically, the perceived change in brightness for our eyes is not linear, so a logarithmic curve tries to correct for this and give a linear perceived brightness change."

The lighting industry supports that explanation. Here's what the Lighting Controls Association, a advice from the National Electrical Manufacturers Association, says about dimming curves:

"An analogy to this is found in sound control. While the 0-10 scale on the knob seems to indicate a linear relationship, in fact, the sound controls are based On a curve that reflects the nonlinear human response to sound, we are more sensitive to changes at low sound levels than high, to make the controls more natural feel an exponential formula for delivering sound level changes. It feels more natural. The answer to light is also nonlinear. We respond to small changes in low light levels more than at high levels. "

So how do different dimming curves actually look?

Glad you asked!

For comparison, let's take the Lifx Mini White LED, which uses a logarithmic dimming curve and the TP-Link Kasa KB100 LED, which uses a linear dimming curve. Each puts out 650 lumens at maximum brightness – but they do not keep synchronization as long as you call things.

  lifx vs vs-kasa dimmer curves-10-100

The top row is a Lifx Mini White LED that uses a logarithmic dimming curve . The bottom line is a TP-Link Kasa KB100 LED, which uses a linear approach. With the linear Kasa LED, you hardly get any noticeable difference in brightness over the upper half of the dimmable area of ​​the lamp.


Chris Monroe / CNET

It is evident that the logarithmic Lifx Mini White LED there in the top row offers a much better variety of brightness settings in the upper half of the dimmable range of the lamp. It depends on the logarithmic approach, which sets the brightness down much faster at the high settings.

It also means that the actual lumen number with Lifx is much lower than what the settings suggest. For example, the 60% setting gives only 220 lumens – about 35% of the lamp's maximum lumen output. With TP-Link, you have to dampen all the way to the 27% setting before turning 220 lumens. It sounds like the Lifx Mini White LED and other logarithmic bulbs that it is out of the target, but they pass the eye test, and that's what matters. The logarithmic setting controls, at least at settings above 50%.

But what about the settings below 50%? Lights with logarithmic dimming curves ring the lumen much faster than their linear counterparts, giving it less space for differentiation at the bottom of the scale. The Philips Hue White LED was the worst annoyance, with only 2 lumens separating the 1% setting from the 10% setting – the Lifx Mini White LED was not much better with a difference of only 7 lumens.

Over at Philips Hue HQ, Yianni explains that it's all relative. "A change of 2 lumen is really a lot for the eyes if you start with 10 lumen, while 2 lumen is insignificant if you have 800 lumen," he told me.

  lifx-vs-kasa dimmer-curves-1-10 "data-original =" https://cnet1.cbsistatic.com/img/XvM9qD-CWJsDFBFCcRWDWoIR3Sw=/2019/05/01/b3a39721-3ef2-4356 -a882-ab3296412388 / lifx-vs-kasa-dimming-curves-2-10.jpg

The script turns at the bottom of each lamp's dimmable range. Now it is the linear Kasa LED lamp (bottom line) that offers clear differences in perceived brightness. At the same time, the logarithmic Lifx LED lamp (top row) hardly changes at all.


Chris Monroe / CNET

But look at the lower settings with Lifx LED compared to Kasa LED. The results are the opposite of what we saw before – it is now the linear Kasa LED that shows clear changes in perceived brightness, while the logarithmic Lifx LED is hardly changed anyway. It is pointless, because light bulbs with linear dimming curves have more lumen to work with at low settings. With Kasa LED, the difference between the settings is 1% and 10% 76 lumens – more than 10 times the difference you get with Lifx.

Download to that point. Which is best?

Neither approach is perfect, but you get a greater number of dimmable settings that pass the eye test if you use a bulb with a logarithmic dimming curve. With logarithmic lights, you do not see much of the difference in brightness between any of the 10 or 15 settings – but with the linear approach, you have the same problem with the entire upper half of the dimmable area of ​​the lamp.

Logarithmic bulbs "fast winding" through the top of the scale where the light control settings are all similar, giving better dimming and a better overall amount of dimmable settings. I just wonder if there is a way to get it both ways – logarithmic fog at the top, and more of a linear approach down the bottom. I continue to test smart light bulbs as if it is my job, and if I find a light bulb then I will let you know everything about it.


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