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Home / Tips and Tricks / Your intelligent light bulbs are not dimmed as you believe. Here is the reason

Your intelligent light bulbs are not dimmed as you believe. Here is the reason



  LED Bulb.jpg

The light emitting diodes in your smart LEDs may not be darkened as you would expect – but there is a good reason for that.


Tyler Lizenby / CNET

"Alexa, set the lights to 50%."

I use voice commands to constantly control the smart lights in my own home. It's Really One of the Best Benefits of Smart Lighting – With a single voice command or a keystroke in an app, you can set your lights to the 100-point scale to exactly the desired brightness, typically at zero flicker, .

Take a closer look at the way that smart light bulbs actually get weaker, and you'll find that these 100-point scales vary from bulb to bulb. For some settings, the brightness is reduced linearly – 10% of the total lumen output at 10%, 60% of the total lumen output at 60% and so on. Set the bulb to 50%, get half the maximum lumens. Sounds reasonable, right?

However, other light bulbs are logarithmic, with lumens quickly dropping to a lower level than expected as you turn things down. Tell Alexa that you should set a light bulb to 50%, and you may only get 25% of the lumens that you would get at full brightness. What gives? Admittedly, the answer is unclear, so be here with me, but it's fascinating and it depends on the difference between measured brightness and perceived brightness. And in the end, the science of how our eyes work supports the logic of logarithmic dimming – but it's not a perfect approach.

What kind of effect can these differences in the dimming curve have when these lamps illuminate your home? I asked myself that.

Read more : Best Cheap Bulbs

This TP-Link LED from Kasa adjusts the brightness linearly while the white LED from Philips Hue uses a logarithmic dimming curve. [19659003] Ry Crist / CNET

Warning: Curves Ahead

To get a look at the dimming curves of these lamps, I've loaded each one into the light sphere of the lighting lab and then measured the brightness at all 100 dimmable settings with the built-in spectrometer. With several hundred readings, this was a tedious process, because dimming an LED consumes less energy and produces less heat. This will make the bulb a little brighter. You can see the effect in this top left TP-link graph – it's a linear approximation to dimming, but when I dimmed it to take measurements, those readings were different from the dotted line that represents the target ,

It's not a noticeable change to the naked eye, but it was a bit painful to plot accurate dimming curves in a Google Sheet. I have done my best to keep the readings as accurate as possible for the purposes of these charts. However, assume and assume a 10% error rate in specific luminal numbers, especially in the middle of each dimming curve.

Read More : The Complete Guide to Philips Hue

I first reviewed some of the relatively affordable Smart Light Bulbs that I wrote about in my article have the latest purchase instructions here on CNET. Four of them – the Philips Hue White LED of the Lifx Mini White, the C by GE Soft White Life LED and the Cree Connected LED – a logarithmic approach to dimming , The other three – the Eufy Lumos Mini LED the Sengled Element Classic LED and the TP Link Kasa KB100 LED – kept things more or less linear.

One obvious difference is that the logarithmic bulbs provide less measurable light than expected in the lower half of the dimming curve. The biggest difference I noticed with the Lifx Mini White LED. At a setting of 50%, I measured 151 lumens. This corresponds to 23.4% of the maximum lumen output of the lamp at 100%.

In addition, logarithmic bulbs like the white Philips Hue LED, which flattens everything at the bottom of this curve, do not make much of a difference in the bottom 15 settings. In fact, the brightness settings of 1% and 10% for the white LED for Hue were separated by only 2 lumens.

"This is intentional Since your eye perceives brightness changes logarithmically, explains George Yianni, chief technology officer of Philips Hue." We design our dimming curve so that strides over the whole area is about equally perceived. "

This Lighting Controls Association diagram gives an idea of ​​what a linear approach to dimming in terms of perceived brightness (blue line) actually looks like too fast for the upper half of the dimmable range and too fast in the lower half of the dimmable range.

Lighting Controls Association

And that's the heart of the argument: a light bulb that uses a linear dimming curve does not make much of a change The perceived brightness in the upper half of this dimmable area as it does not fade fast enough. In other words, the settings above 50% all look very similar.

The logarithmic approach causes you to immediately notice a change in perceived brightness as you deselect things. Basically, you want the measured brightness of a bulb to decrease rapidly as you gradually deselect downward in the upper half of the dimmable area and then gradually deselect the lower half.

Lifx explained its own logarithmic dimming curve in a similar way. "We're more sensitive to changes in subdued light sources than bright light sources," says Lifx spokesman Charlie Felton. "Basically, the perceived brightness change is not linear to our eyes, so a logarithmic curve tries to correct it and cause a linear perceived brightness change."

The lighting industry supports this explanation. The Lighting Controls Association, a council of the National Electrical Manufacturers Association, says about dimming curves:

"An analogy is found in audio control, while the button's 0-10 scale indicates a linear relationship Audio controls on a curve that reflects the nonlinear response of humans to the sound: We are more sensitive at low sound levels than at high volumes, so an exponential formula is used to allow for sound level changes that feels more natural, and the response to light is also non-linear We tend to respond to small changes in low light conditions than high ones. "

So, how do different dimming curves look like?

I'm glad you asked!

For comparison, we use the white Lifx LED, which uses a logarithmic dimming curve, and the TP-Link Kasa KB100-LED, which uses a linear dimming curve. At maximum brightness, about 650 lumens each are output. However, they do not stay in sync as long as you select the settings down.

  lifx vs kasa dimming curves 10-100

The top row is a white Lifx LED that uses a logarithmic dimming Curve. The bottom row is a TP-Link Kasa KB100 LED, which uses a linear approach. The linear LED from Kasa detects almost imperceptible differences in brightness in the upper half of the dimming range of the bulb.


Chris Monroe / CNET

It is obvious that the logarithmic Lifx Mini White LED in the top row offers a much better choice of brightness settings in the upper half of the dimmable range of the bulb. This is due to the logarithmic approach, where the brightness is slowed down much faster at these high settings.

This also means that Lifx's actual lumens are much lower than the settings suggest. For example, the 60% setting provides only about 220 lumens – about 35% of the maximum lumen output of the lamp. With TP-Link you have to dim down to 27% before reaching 220 lumens. This may sound like the Lifx Mini White LED and other logarithmic light bulbs would not reach the target, but they pass the eye test, and that's what matters. The logarithmic approach is checked, at least for settings above 50%.

But what about the settings below 50%? Lamps with logarithmic dimming curves lower the lumens much faster than their linear counterparts. This leaves less room for differentiation at the bottom of the scale. The Philips Hue White LED was the worst offender. Only 2 lumens separated the 1% setting from the 10% setting – the Lifx Mini White LED was not much better with a difference of only 7 lumens.

Past the Philips Hue HQ Yianni explains that everything is relative. "A change of 2 lumens is really great for your eyes when you start with 10 lumens while 2 lumens are insignificant when you're at 800 lumens," he told me.

  lifx-vs-kasa-dimming-curves-1-10 "data-original =" https://cnet1.cbsistatic.com/img/XvM9qD-CWJsDFBFCcRWWoIR3Sw=/2019/05/01/b3a39721-3ef2-4356 -a882-ab3296412388 / lifx-vs-kasa-darkening-curves-2-10.jpg

The script is being turned down in the dimmability of every incandescent bulb. Now it is Kasa's linear LED (bottom row), which has significant differences in perceived brightness. Meanwhile, the logarithmic Lifx LED (top row) hardly changes.


Chris Monroe / CNET

Take a look at the lower settings with the Lifx LED compared to the Kasa LED. The result is the opposite of what we have seen before. Now, the linear Kasa LED shows significant changes in perceived brightness, while the logarithmic Lifx LED barely changes. This makes sense because lamps with linear dimming curves have more lumens at low settings. For the Kasa LED, the difference between the 1% and 10% settings is 76 lumens – more than ten times the difference you get with Lifx.

Getting to the point. Which is the best?

No 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 bulbs, you will not notice a large difference in brightness between the lower 10 or 15 settings. With the linear approach, you have the same problem with the entire upper half . the dimmable area of ​​the lamp.

Logarithmic bulbs go through the upper part of the "fast forward" scale, with the brightness settings all looking the same. This leads to a better dimming and overall better dimming. I'm just wondering if there's a way to have both possibilities – logarithmic dimming above and more linear approach below. I'll test smart bulbs like it's my job, and if I find such a light bulb, I'll let you know.


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