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Relatively recently, household LED lighting sources began to be massively offered for sale. They quickly won the hearts of numerous buyers.
This was facilitated by such technical advantages as low power consumption combined with a long service life, as well as an eye-friendly emission spectrum.
From the article you will learn why the LED lamps are flashing, the causes and ways to eliminate them.
The main advantages and disadvantages of LED lamps
An important advantage of LED lamps is their interchangeability in size and mounting cartridge with traditional incandescent lamps.
A few shortcomings of household LED sources in the form of high cost, a certain degradation of the brightness of the glow over time, and the sensitivity of some samples to the quality of the power supply network were considered as secondary and slightly restrained the spread of these lamps.
Operating experience has shown that LED lamps are sometimes characterized by a flashing of the emitted light. This unpleasant effect occurs with varying frequency and intensity.
Sometimes this becomes a consequence of the low quality of the lamp itself, and in some cases it can be eliminated without changing the lamp, without involving complex measuring instruments and without calling a specialist.
Design
To understand the causes of blinking and ways to correct this shortcoming, consider the main design features of the LED lamp.
The functions of the radiating element of this source are performed by a set of semiconductor crystals, the pn-junction of which, when a direct current flows, begins to generate light in the visible wavelength range.
The LED is a point source, therefore, in order to obtain uniform radiation, individual crystals are connected in series-parallel chains, placed on a supporting base according to a special scheme.
The spectral composition of the emitted light can be adjusted by various additives to the crystal material, and the brightness of the glow can be changed over a wide range by changing the magnitude of the forward current.
For heat dissipation, a developed metal radiator is used. All structural elements are mounted on a plastic bearing base, equipped with a standard base, and closed with a protective glass flask.
From the network, an alternating voltage is supplied to the lamp, which, according to GOST, can vary within a fairly wide range.
To obtain the direct current necessary for the operation of semiconductor emitters, a so-called driver is necessarily introduced into the composition of the lamp.
It is understood as a device that provides rectification of alternating current and its stabilization when the mains voltage changes within those nominal tolerances that are allowed by the network standards.
For the working elements of the lamp, the driver performs the functions of a multifunctional current source, the older models of which provide:
- galvanic isolation of radiating crystals from a 220-volt network, which is a necessary condition for their long service life;
- obtaining direct current from alternating;
- stabilization of the current through the crystals with changes in the mains voltage;
- suppression of various ripples and impulse noise induced in the network.
Schematic features of the LED lamp
Unlike traditional light sources, the LED lamp as a light source has a very low inertia and an almost linear dependence of the radiation brightness on the flowing current.
Therefore, even small current measurements immediately lead to changes in the luminous flux, which are perceived by the eye as blinking or flashing.
The LED has a very high current-voltage slope, as shown in Figure 1. Therefore, small changes in the voltage applied to it cause large changes in current and, accordingly, change the brightness of the lamp.
Moreover, a consequence of the low inertia and high sensitivity to voltage changes is that the LED lamp can flash even when the switch is off.
In some cases, this unpleasant effect manifests itself when the wiring is fully operational and the voltage meets the requirements of the standards.
It should be noted that brightness pulsations are further divided into low-frequency ones, which are clearly visible to the naked eye, and high-frequency ones, which are not so replacements, but still cause increased fatigue, lead to headaches and other unpleasant consequences with prolonged exposure to the eyes.
An accurate determination of their quantitative parameters is possible only with the help of an oscilloscope and other measuring instruments.
Further, the main causes of the appearance of pulsations in the brightness of the radiation are considered and recommendations are given for their elimination.
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Flashing in normal light mode
The reasons for the unstable operation of the included LED lamp are quite diverse.
Insufficient filtration efficiency
As it is not trite, but the well-known rule of inevitable financial losses for miserly often manifests itself in LED lighting technology.
The user’s desire to save money and buy cheap products instead of high-quality ones can potentially lead to flashing even with a fully functional light bulb, the normal glow of which was demonstrated by the seller upon purchase.
The current sources of many lamps of Chinese and, which is especially unpleasant, of domestic production, instead of a full-fledged driver, are implemented on the basis of a simple circuit, similar to the one shown in Figure 2.
They are assembled on one of the varieties of the diode bridge D1 – D4, in series with which the output smoothing capacitive filter C2 – Rf is connected.
The input voltage is reduced to a predetermined value by a chain of quenching resistor Rg and smoothing capacitor C1 connected in parallel.
The filter effectively removes residual ripples of the current rectified by the bridge at standard mains voltage parameters. At the same time, he is not able to cope with impulse noise, which leads to flashing.
In addition, the slightest deviations of the input voltage from the specified one due to the high steepness of the current-voltage characteristic are accompanied by significant changes in current, which immediately affects the brightness of the glow.
The situation in this case is not hopeless and can be corrected by increasing the filter smoothing factor. In this case, you can take advantage of the fact that a constant voltage is applied to the LEDs, which allows the use of an electrolytic capacitor Cd, which is highlighted in Figure 3 in a red circle and soldered in parallel with the smoothing capacitor C1.
The power supply of an LED lamp, even of the middle class, is a full-fledged driver, which includes an integrated current regulator (usually implemented according to the PWM scheme).
The latter maintains a constant current through the diodes due to the presence of a stabilizing negative feedback.
Reduced mains voltage
The lamp driver provides the required current only in a certain range of power voltage changes. With a significant difference in voltage from 220 V, the driver sooner or later enters the mode of unstable operation, in which the non-linearity of its circuit elements begins to have a significant impact on the magnitude of the output current.
At the same time, the current itself becomes pulsating: for most of the time, when it is not enough to maintain a normal glow level, the charge accumulates in the capacitor.
Then the driver briefly enters the normal mode, during which the capacitor is quickly discharged, after which the lamp sharply reduces the light output or even turns off completely.
In this case, the cause of the ripples can be found with an ordinary tester, which measures the mains voltage, and the main means of struggle is to increase it to a predetermined level with an autotransformer.
Availability of dimmers
The dimmer or soft dimmer was originally designed for incandescent lamps and therefore does not work well with most LED lamps.
This is due to the fact that the typical design of this component is designed for a minimum load power of about 50 W, which is much higher than the power of LED sources.
With less power in the load, the control circuits of the dimmer are not able to correctly supply voltage to the lamp, which externally manifests itself in the form of its flashing.
In any case, the dimmer should be originally designed for LED sources.
In some situations, flickering can be dealt with by switching the regulation from rising to falling edge, which is available for older models of these devices.
See also:
What are dimmers: device, principle of operation in LED lamps, a lamp, a radio tape recorder
Flashing off
The LED lamp as a light source has a very low inertia.
This feature leads to the fact that even with small pulsed currents passing through the LEDs, the lamp turns on for a short time, which is visually perceived as a flash.
Despite the various reasons for the appearance of this phenomenon, the common thing here is the flow of current into the LEDs through circuits not intended for this.
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Illuminated switches
When creating electrical house wiring, backlit switches are quite popular, which are easy to find at night when the lights are off due to the glow of the LED or neon light bulb built into the key.
De facto, this source shunts the switch, resulting in a permanently closed circuit.
Even a small current passing through this circuit is able to charge the dimmer smoothing filter capacitor, which, when discharged to the lamp, is quite capable of causing it to turn on for a short time.
You can correct the situation by shunting the lamp with a resistor with a resistance of about 1 MΩ and a power of at least 0,5 W, which is highlighted in Figure 4 with a red circle.
Poor isolation of power cables
Sometimes, when creating house wiring, power cables for connecting powerful and ordinary consumers are mistakenly or, out of an effort to reduce the cost of repairs, laid in one strobe or other channel instead of the location required by the rules in different channels.
Due to the presence of electromagnetic coupling between the current flow circuits, when a powerful consumer is turned on, a current is also induced in the cable to which the LED voltage source is connected. In schematic form, this case is shown in Figure 5.
In some cases, the induced current is sufficient to charge the LED lamp driver capacitors and cause the lamp to turn on momentarily.
The magnitude of the parasitic current increases if a powerful consumer distorts the original sinusoidal form of the AC mains voltage.
This situation is typical for cheap household appliances, which are equipped with switching power supplies with an insufficient degree of decoupling of their internal circuits with 220-volt wiring.
Also read how to check filament lamps for flashing.
Error in connecting wires to the switch
Figure 5 shows a typical case of improper wiring of lighting circuits, which, when using LED lamps, can potentially lead to their flickering.
The root cause of its occurrence is that quite often, when installing power wiring, cheap wires with the same insulation color are used, for which it is difficult to determine zero and phase.
At the same time, the provision on the need to connect the phase wire to the switch is not observed, which is shown on the right side of this Figure 6.
Some electricians and inexperienced home craftsmen do not pay attention to the need to comply with this rule, since with ordinary incandescent lamps its violation is not accompanied by any negative consequences.
In the case of LED technology, this error leads to the fact that the phase is constantly present on the lamp.
Due to the inevitable leakage microcurrents, which are present even in serviceable wiring, the driver capacitors are gradually charged, followed by a short-term switching on of the lamp.
To eliminate this malfunction, it is enough to check with a probe that the phase is connected correctly and, if necessary, swap the wires.
See also:
Conclusion
The foregoing allows us to state that the physics of the LED lamp makes it initially prone to flashing. This unpleasant effect is not a fundamental disadvantage of this type of light source.
The reasons for its occurrence are quite diverse: from the use of cheap products to flaws in the wiring and installation errors.
In the case of using high-quality technology, blinking is easily eliminated at home using the simplest tools with the desire and a minimum level of knowledge.