Our A19 and A21 lamps fit in standard lamp fixtures and are perfect for floor and desk lamp fixtures.
Our candelabra LED bulbs offer soft and warm light output in a decorative bulb style that fits E12 lamp fixtures.
BR30 lamps are ceiling lamps that fit in residential and commercial fixtures with 4-inch or wider openings.
Directly replace 4-ft fluorescent lamps with our T8 LED tube lights, compatible both with and without ballasts.
LED tube light fixtures pre-wired and compatible with our T8 LED lamps.
Linear lamp fixtures in 2-ft and 4-ft lengths. Plugs into standard wall outlets nd mounts using screws or magnets.
Overhead light fixtures with hanging chains. Plugs into standard wall outlets.
We offer 365 nm and 395 nm LED lights for fluorescence and curing applications.
We offer 270 nm UV-C LED lights for germicidal applications.
LED PCBs, panels and other form factors for a variety of industrial and scientific applications.
Bright LED emitters mounted on a flexible circuitboard. Can be cut-to-length and installed in a variety of locations.
Dimmers and controllers to adjust LED strip lighting system brightness and color.
Power supply units to convert line voltage to low voltage DC needed for LED strip light systems.
Extruded aluminum channel profiles for mounting LED strip lights.
Solderless connectors, wires and adapters to join and connect LED strip light system components together.
LED strips come in a very wide variety of sizes, densities and color quality , but what they all have in common is that at some point, you may run into some difficulty getting them to work. Through our many years of working with LED strips, we've put together some of the most common causes of LED strip problems and what you can do to solve them.: Low voltage DC electronics are generally considered safe and pose a relatively low shock hazard. However, whenever possible, we strongly recommend that you turn off the power to, or unplug, the power supply prior to testing or adjusting any LED strips or accessories.Note that in some troubleshooting steps we suggest below, you will need to have the power supply plugged in and powered up to complete the test. Use caution and seek the advice of a qualified individual if you are not sure how to perform these tests safely.You've connected the power supply to the LED strip, turned the switch on, and...nothing. What gives?To troubleshoot, try the following steps:If, for example, your power supply is 12V DC, it will not work with a 24V LED strip. Check the back of the power supply unit, which will have the output voltage marked. Then, check the LED strip itself, which will have its input voltage marked at the LED strip connection points.A quick test using a multimeter to verify the voltage across the two output wires, or voltage between the DC plug's inner pin and outer barrel should indicate a voltage differential. If it shows a voltage less than its rated voltage, you may have a malfunctioning power supply.Note that the power supply must be powered up for this test.This post contains affiliate links. If you use these links to buy something we may earn a commission.Remove any optional dimmers and controllers from the circuit, and determine if you can get the LED strip to illuminate without the extra accessories. If the LED strip works, that means you have a problem with the dimmer or controller, or the connection leading up to or from those accessories.Note that the power supply must be powered up for this test.This should go without saying, but never connect a low voltage DC (e.g. 12V/24V) LED strip directly to a mains voltage (e.g. 120V/240V) wall outlet!Make sure all of your connectors and wires are in place and have not fallen out. Try tightening screws on DC adapters , and re-inserting LED strips into solderless connectors , which are common contact failure points.If you have a multimeter, test each point along the circuit for a voltage differential between the positive and negative (ground) wires / terminals. Start at the power supply's DC output and make your way to the LED strip. If the LED strip's positive and negative copper pads do not have a voltage differential, power is not being fed to the LED strip due to a malfunction before the power can even reach the LED strip section.Especially if you are soldering your own wires instead of using solderless accessories, you may have inadvertently created a short circuit by allowing the positive and negative wires to come in contact.Perform a quick visual check of your entire LED strip connections and ensure that these wires are sufficiently separated.Short circuits of this type are especially more likely when working with multi-channel strip lights such as 5-color LED strips which have 6 connection points.If after a visual check you did not find any visible short circuits, you may next want to check for invisible short circuits. The quickest way to test this is to again, use a multimeter.Apply the multimeter contacts to the positive (+) and negative (-) copper pads on the LED strip, and test for the resistance value. If there is no short circuit, the multimeter should indicate infinite resistance. If it indicates any resistance value, that indicates that there is a short circuit.If there is an indication of a short circuit, disconnect any accessories and wires, and determine if the short circuit on the LED strip persists. If it does, this is an indication that there is an issue with the LED strip.One common short circuit location is the cut-line of the LED strip where scissors were used. LED strips are typically constructed of two copper layers, separated by a thin layer of insulation. In some cases, if the scissors do not make a clean cut, the insulating layer may fail at the cut point, creating a short circuit.If you've identified a short circuit on an LED strip segment but cannot find any visible signs of a short circuit location, try cutting off the last 1-2 inches of the LED strip on both ends to remove the potentially damaged cut-line segment. We recommend using a sharp pair of scissors to ensure a clean cut, as dulled, blunt scissors are more likely to "squash" the copper and insulation layers, creating the short circuit.Is your LED strip running fine, but exhibiting a noticeably lower brightness at one end? This is a commonly observed issue with lower quality LED strips, and its primary cause is voltage drop. Voltage drop is essentially caused by excessive electrical current for a given circuit design, or excessive resistance in the circuitry, or a combination of both.Most LED strips will have a recommended max run length based on its power draw per foot and the internal circuit design. Because each section of LED strip must carry the current for all "downstream" LED strip segments, connecting too long of an LED strip will exceed the power rating for the LED strip sections connected closest to the power source.The most immediate consequence of overloading an LED strip with too much power is voltage drop, whereby the voltage supplied to each section of LED strip progressively decreases as one moves further away from the power supply. The reason the voltage decreases is due to the internal resistance in the copper traces of the PCB.Don't forget that wires connecting to or between LED strips also have internal resistance, and using wires with insufficient thickness can also result in excessive voltage drop. Check out our online wire gauge calculator to see if your wire spec is sufficient for your setup.Perhaps you may be able to rearrange your circuit be configured in "parallel" as opposed to "series." Excessive electrical resistance can be caused by poor electrical contact and corroded copper. Check your LED strip wiring and ensure all contacts are clean and sufficient.In extreme cases, poor contact points can heat up, leading to a fire hazard, so determining and eliminating these situations can be an important safety check.The most definitive way to determine if voltage drop is causing issues for your LED strip is to simply measure the voltage between the copper pads at various points along the LED strip. If the voltage progressively decreases as you move further away from the power source, this is a sign of voltage drop.Almost all LED strips will exhibit some voltage drop, and whether it becomes a significant problem or not primarily depends on the extent of the voltage drop. For example, a 12V LED strip may drop to 11.5V at the end furthest from the power supply, but this is typically not a significant enough voltage drop to warrant any concern. If, on the other hand, voltage drops to below 10V, this is a sign that there is a significant amount of voltage drop that is very likely producing a very noticeable brightness drop.If your LED strips are losing brightness across the entire strip, this could be caused by two issues:To determine which of these two issues is to blame, first determine the input voltage at the point where the LED strip is connected to the power supply (i.e. the first pair of copper pads).If the input voltage here is below the expected voltage (e.g. 10V for a 12V LED strip) you are likely seeing an issue with the power supply or a loose / corroded connection between the LED strip and the power supply.The good news is that your LED strip is likely in OK shape, and simply correcting your wiring or replacing your power supply will resolve your issue.If in the first test you determined that the LED strips are being fed the full design input voltage (e.g. 12V for a 12V system) but you are still seeing a brightness drop, you may have a serious issue with the LED strip. LEDs are generally designed to last more than 36k hours , but some lower quality products will cut corners in design and manufacturing, leading to premature failures. In such situations, your only choice may be to replace the LED strip entirely.If parts of your LED strip are falling from their mounted surface, you may have used an LED strip with insufficient double sided tape. You can consider reapplying a new layer of double sided tape, or using some mounting brackets and screws for a more permanent mounting method.We recommend "sticking" with higher quality LED strip lights , which are more likely to specify higher adhesion double sided tape, such as 3M VHB.If you have an entire LED strip segment illuminated but notice a section of 3 LEDs (or 6 LEDs for 24V) that remain dark, you may have an "open circuit" in one of the sections.What this means is that due to a manufacturing flaw or some mechanical damage during shipping or installation, one of the LEDs or components for a single section has come loose, resulting in a complete electrical disjoint for just that section of LEDs.If you are familiar with how to solder, you may want to try reheating the solder joints for each of the LEDs and components along that dead section. If not, your best bet would be to ask your supplier for a replacement (if they provide a warranty) or simply remove the failed section by cutting along the cut-lines and rejoining the two segments together using connector clips. Waveform Lighting manufactures LED strips to exacting quality and reliability specifications in order to avoid common issues like the ones outlined above. Unfortunately the same cannot be said for many other "budget" LED strip lights that are available for purchase.Please contact us immediately if you have an issue with an LED strip light that you purchased from us. Even if you're having trouble with an LED strip light that you purchased elsewhere, we'd be more than happy to help and discuss replacement options.
In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED. The voltage drop across an LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current. Very simple circuits are used for low-power indicator LEDs. More complex, current source circuits are required when driving high-power LEDs for illumination to achieve correct current regulation.
Basic circuit
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The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat.
An LED has a voltage drop specified at the intended operating current. Ohm's law and Kirchhoff's circuit laws are used to calculate the appropriate resistor value, by subtracting the LED voltage drop from the supply voltage and dividing by the desired operating current. With a sufficiently high supply voltage, multiple LEDs in series can be powered with one resistor.
If the supply voltage is close or equal to the LED forward voltage, then no reasonable value for the resistor can be calculated, so some other method of current limiting is used.
Power source considerations
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The voltage versus current characteristics of an LED is similar to any diode. Current is approximately an exponential function of voltage according to the Shockley diode equation, and a small voltage change may result in a large change in current. If the voltage is below or equal to the threshold no current flows and the result is an unlit LED. If the voltage is too high, the current will exceed the maximum rating, overheating and potentially destroying the LED.
LED drivers are designed to handle fluctuation load, providing enough current to achieve the required brightness while not allowing damaging levels of current to flow. Drivers may be constant current (CC) or constant voltage (CV). In CC drivers, the voltage changes while the current stays the same. CC drivers are used when the electrical load of the LED circuit is either unknown or fluctuates, for example, a lighting circuit where a variable number of LED lamp fixtures may be installed.
As an LED heats up, its voltage drop decreases (band gap decrease[1]). This can encourage the current to increase.
MOSFET drivers
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Household LED light bulb with its internal LED elements and driver circuitry exposed.An active constant current source is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which might increase the useful life of batteries. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limiter.[2] Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage.
Switched-mode power supplies (e.g. buck, boost, and buck-boost converters) are used in LED flashlights and household LED lamps. Power MOSFETs are typically used for switching LED drivers, which is an efficient solution to drive high-brightness LEDs. Power integrated circuit (IC) chips are widely used to drive the MOSFETs directly, without the need for additional circuitry.[2]
Series resistor
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Series resistors are a simple way to stabilize the LED current, but energy is wasted in the resistor.
Miniature indicator LEDs are normally driven from low voltage DC via a current-limiting resistor. Currents of 2 mA, 10 mA and 20 mA are common. Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficiency tends to reduce at low currents,[3] but indicators running on 100 μA are still practical.
In coin cell powered keyring-type LED lights, the resistance of the cell itself is usually the only current limiting device.
LEDs with built-in series resistors are available. These may save printed circuit board space, and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However, the resistor value is set at the time of manufacture, removing one of the key methods of setting the LED's intensity.
The value for the series resistance may be obtained from Ohm's law, considering that the supply voltage is offset by the voltage drop across the diode, which varies little over the range of useful currents:
R = V p o w e r − V l e d − V s w i t c h I l e d {\displaystyle R={V_{power}-V_{led}-V_{switch} \over I_{led}}}
or
I l e d = V p o w e r − V l e d − V s w i t c h R {\displaystyle I_{led}}={V_{power}-V_{led}-V_{switch} \over R}
where:
R {\displaystyle R}
ohms, typically rounded up to the next higher resistor value.V p o w e r {\displaystyle V_{power}}
volts, e.g. 9-volt battery.V l e d {\displaystyle V_{led}}
V f {\displaystyle V_{f}}
band gap, a blue LED may drop around 3 to 3.3 volts. Light-emitting diode physics § Materials has a list of colors with their voltage drop ranges.V s w i t c h {\displaystyle V_{switch}}
BJT transistor, useV C E ( s a t ) {\displaystyle V_{CE(sat)}}
I l e d {\displaystyle I_{led}}
amps. The maximum continuous-on current is shown on LED datasheets, for example 20 mA (0.020A) is common for most small LEDs. Many circuits operate LEDs at less than the specified maximum current to save power, or to reduce brightness, or to use a common resistor value. For indoor use, tiny surface mount high-efficiency LEDs can easily light up with 1 mA (0.001A) or more current, which most digital logic outputs can easily source or sink.Using the algebraic formula (above) and assuming V s w i t c h {\displaystyle V_{switch}} is 0 (to simplify examples), the resistance is calculated as follows:
V p o w e r {\displaystyle V_{power}}
V l e d {\displaystyle V_{led}}
I l e d {\displaystyle I_{led}}
R {\displaystyle R}
common resistor values).V p o w e r {\displaystyle V_{power}}
V l e d {\displaystyle V_{led}}
R {\displaystyle R}
I l e d {\displaystyle I_{led}}
LED arrays
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Schematic of LEDs in seriesSchematic of LEDs in parallelStrings of multiple LEDs are normally connected in series. In one configuration, the source voltage must be greater than or equal to the sum of the individual LED voltages; typically the LED voltages add up to around two-thirds of the supply voltage. A single current-limiting resistor may be used for each string.
Parallel operation is also possible but can be more problematic. Parallel LEDs must have closely matched forward voltages (Vf) in order to have similar branch currents and, therefore, similar light output. Variations in the manufacturing process can make it difficult to obtain satisfactory operation when connecting some types of LEDs in parallel.[4]
LED display
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LEDs are often arranged in ways such that each LED (or each string of LEDs) can be individually turned on and off.
Direct drive is the simplest-to-understand approach—it uses many independent single-LED (or single-string) circuits. For example, a person could design a digital clock such that when the clock displays "12:34" on a seven-segment display, the clock would turn on the appropriate segments directly and leave them on until something else needs to be displayed.
However, multiplexed display techniques are more often used than direct drive, because they have lower net hardware costs. For example, most people who design digital clocks design them such that when the clock displays "12:34" on a seven-segment display, at any one instant the clock turns on the appropriate segments of one of the digits—all the other digits are dark. The clock scans through the digits rapidly enough that it gives the illusion that it is "constantly" displaying "12:34" for an entire minute. However, each "on" segment is actually being rapidly pulsed on and off many times a second.
An extension of this technique is Charlieplexing where the ability of some microcontrollers to tri-state their output pins means larger numbers of LEDs can be driven, without using latches. For N pins, it is possible to drive n2-n LEDs.
The use of integrated circuit technology to drive LEDs dates back to the late 1960s. In 1969, Hewlett-Packard introduced the HP Model 5082-7000 Numeric Indicator, an early LED display and the first LED device to use integrated circuit technology. Its development was led by Howard C. Borden and Gerald P. Pighini at HP Associates and HP Labs, who had engaged in research and development (R&D) on practical LEDs between 1962 and 1968.[5] It was the first intelligent LED display, making it a revolution in digital display technology, replacing the Nixie tube and becoming the basis for later LED displays.[6]
Polarity
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Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with the correct electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated with alternating current, but they will only light on the half of the AC cycle where the LED is forward-biased. This causes the LED to turn on and off at the frequency of the AC supply.
Most LEDs have relatively low reverse breakdown voltage ratings compared to standard diodes, so it may be easier than expected to enter this mode and cause damage to the LED due to overcurrent. However, the cut-in voltage is always less than the breakdown voltage, so no special reverse protections are necessary when driving an LED directly from an AC supply when properly current-limited for forward-biased operation.
The manufacturer will normally advise how to determine the polarity of the LED in the product datasheet. However, there is no standardization of polarity markings for surface mount devices.[7][8]
Pulsed operation
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Many systems pulse LEDs on and off, by applying power periodically or intermittently. So long as the flicker rate is greater than the human flicker fusion threshold, and the LED is stationary relative to the eye, the LED will appear to be continuously lit. Varying the on/off ratio of the pulses is known as pulse-width modulation (PWM). In some cases, PWM-based drivers are more efficient than constant current or constant voltage drivers.[3][9]
Most LED data sheets specify a maximum DC current that is safe for continuous operation. Often they specify some higher maximum pulsed current that is safe for brief pulses, as long as the LED controller keeps the pulse short enough and then turns off the power to the LED long enough for the LED to cool off.
LED as a light sensor
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Mobile phone IrDAIn addition to emission, an LED can be used as a photodiode in light detection. This capability may be used in a variety of applications including ambient light detection and bidirectional communications.[10][11][12]
As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sensitive to blue light and some green light, but not to yellow or red light.
This implementation of LEDs may be added to designs with only minor modifications in circuitry.[10] An LED can be multiplexed in such a circuit, such that it can be used for both light emission and sensing at different times.[10][12]
See also
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References
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