The relatively new LED filament lamps are a genious invention, they look really great.
Technically they can also be good, but with regard to light flicker, unfortunately so bad, that they could rather be used as stroboscopes instead of lighting.
Short cuts to CFD information,
the possibility to have the light flicker measured.
As already described in the article "The boob tube grilled", however, there is no information about light flicker on the illuminants package.
The electronic ballast is massively responsible for how well illuminants are regarding light flicker. If it is inadequate, then the illuminants flicker like glow lamps.
Correspondingly, Der Lichtpeter has measured over 520 different LED filament lamps and has come to a largely frightening result:
For the E27 products, the CFD span ranges from flicker-free to stroboscope-like just below 60%.
With the E14 products, any CFD value can be seen between flicker-free via bad 50% and worst 100%. "Dimmables" often flicker extremely, because they only partly emit light pulses. In this respect, the 2W - approx. 200 lumens of luminaires, especially those in DIY stores or on the rummage tables of other markets, are predominantly affected.
Here is the good example of the light emission of a virtually flicker-free LED filament lamp as a true retrofit candle in the E14 socket. We see: It is technically feasible. This light is significantly better than that of an incandescent lamp; it is equal to daylight.
The light emission of this filament lamp operated directly at mains voltage, shows a massive stroboscopic effect, the duty cycle between light and dark is just below 50%. This kind of light must be avoided in accordance with DIN EN 12464-1. It is classified as hazardous for work, because cyclic movements can not be perceived properly.
140 of 320 different E14 LED filaments have a similar light signature.
Can't be any worse.
If the average brightness of the above shown dimmable LED filament lamp is dimmed to 25% (with a dimmer correctly run with its minimum load), then the light is emitted only in the form of needle pulses. The stroboscopic effect is even much stronger, the light-to-dark ratio is around 12%.
This is no more light, ...
... because a hand moving through this light shows the effectiveness (single picture taken with an exposure duration of about 200 ms). In a discotheque this light may be desirable as a special effect, but certainly not as a cozy lighting in the good living room. Whoever moves in a room filled with this light can also lose the balance.
This flicker behavior can be explained as follows:
As with LED filaments, electrically about 50 COB-Leds are connected in series. A minimum voltage of 170V is required to allow current to flow at all. However, this voltage is only reached in the upper part of the sine-wave alternating voltage of 230V/50Hz, which is almost 5 ms in time. In the other period (other 5ms) the LED remains pitch dark. Only if a rectifier and a sufficiently large capacitor are installed in the base, the voltage can be reduced to min. 180V and thus current always flows and permanent light is achieved. This is saved on the China cheap products.
Admittedly: In the E14 socket is not much space for enough cheap electronics, but that should be no reason for bad light. So they do almost without any electronics.
Since Jan. 2017, there are a few manufacturers who offer flicker-free E14-candles without base extension. Since the middle of 2017 even the first dimmable low-flicker E14-filament candle without base extension is available > so it is possible.
The test with a turntable that uses a strobe light to adjust the speed also shows it as expected:
The E14s are the purest stroboscope, the whole turntable seems to stand still, the flickering filament lamp fulfills the job of a stroboscope lamp.
Never since the LED rope lights has there been so much flickering light. In contrast to the rope lights, however, illuminants are supposed to illuminate an object or a room instead of only themselves (decoration). So much flickering can really be unhealthy.
Stroboscope light is to be avoided at workplaces according to DIN EN 12464-1, which can not be good otherwise.
Illuminants that do not meet this standard should actually by today have declared a limitation on usability: "Not suitable for working". Here is a gap in the EU labeling regulation.
So watch out when purchasing LED filament lamps!
You can use the quick tests to get a first-aid overview of whether the light is flickering too much.
There was a time of no information on color temperature in Kelvin or the color rendering index in Ra for LED lamps. If one of the values is missing today, then probably hardly anyone will buy the product.
This should also be so for light flicker, each manufacturer should specify it in the technical data.
If the CFD is low, then this is a good sales argument. If it is not available, it can be interpreted as an inferior quality.
One should ask his vendor for the amount of light flicker or if cannot provide it:
DO NOT BUY!
More about light flicker on Wikipedia and in this flicker blog by Wolfgang Messer.