Frequently Asked Questions about LED Lights & Power Supply

Motion Sensor LED Tube

There has two main motion sensor LED tubes: PIR sensor (infrared sensor) and microwave sensor.

The difference between infrared sensor and microwave sensor:

Infrared detectors will be affected by temperature, airflow, dust and smoke, infrared sensing controller usually for indoor use. But microwave sensing controller completely avoid the effects of temperature, air, dust and smog.

Infrared sensor is good for detecting the human being.
Microwave sensor is good for detecting the moving of the people or things (cars or others).

Click to download the introduction of our LED tube light with PIR sensor:

Integrated LED Tube Light PIR Sensor-Data sheet

Motion sensor T8 LED Tube is widely used for car park lighting,warehouse and office lighting.

Motion Sensor is very helpful and plays an important role nowadays.

The main purpose of motion detection is to sense an intruder and send an alert to your control panel, which alerts your monitoring center. Sensors work when you are not home, or when you tell the system you are not there. Some security systems can be programmed to record events via a security camera when motion is detected.

Motion sensors stand guard, ready to react to various situations, such as movement in your living room, windows or doors being opened or closed, or a broken window. Motion sensors can:

Alert you in the event that your teen breaks curfew
Trigger a doorbell when someone approaches the front door
Alert you when kids enter restricted areas in the home, like the basement, workout room, or medicine cabinet
Save energy by using motion sensor lighting in unoccupied spaces
Notify you if pets enter areas where they’re not supposed to be

To open and close automatic Doors
To turn on and off automatic water faucets and toilets
To turn on lights when a person enters a room
To control ATM displays
At automatic ticket gates
For some parking meters

Types of Motion Sensors

Passive Infrared (PIR)

Detects body heat (infrared energy). Passive infrared sensors are the most widely used motion in home security systems. When your system is armed, your motion sensors are activated. Once the sensor warms up, it can detect heat and movement in the surrounding areas, creating a protective “grid.” If a moving object blocks too many grid zones and the infrared energy levels change rapidly, the sensors are tripped.

The IR sensor itself is housed in a hermetically sealed metal can to improve noise/temperature/humidity immunity. There is a window made of IR-transmissive material (typically coated silicon since that is very easy to come by) that protects the sensing element. Behind the window are the two balanced sensors. PIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don’t wear out. For that reason they are commonly found in appliances and gadgets used in homes or businesses. They are often referred to as PIR, “Passive Infrared”, “Pyroelectric”, or “IR motion” sensors.
PIRs are basically made of a pyroelectric sensor (which you can see in left picture as the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. The sensor in a motion detector is actually split in two halves. The reason for that is that we are looking to detect motion (change) not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.

PIR sensors are more complicated than many of the other sensors explained in these tutorials (like photocells, FSRs and tilt switches) because there are multiple variables that affect the sensors input and output.

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can ‘see’ out past some distance (basically the sensitivity of the sensor). When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.

MircoWave (MW):

Sends out microwave pulses and measures the reflection off a moving object. They cover a larger area than infrared sensors, but they are vulnerable to electrical interference and are more expensive.

Dual Technology Motion Sensors:

Motion sensors can have combined features in an attempt to reduce false alarms. For example, a passive infrared (PIR) sensor could be combined with a microwave sensor. Since each operates in different areas of the spectrum, and one is passive and one is active, Dual Technology motion sensors are not as likely as other types to cause false alarms, because in order for the alarm to be triggered, both sensors have to be tripped. However, this does not mean that they never cause false alarms.

Area Reflective Type:

Emits infrared rays from an LED. Using the reflection of those rays, the sensor measures the distance to the person or object and detects if the object is within the designated area.

Ultrasonic:

Sends out pulses of ultrasonic waves and measures the reflection off a moving object.

Vibration:

Detects vibration. These can be purchased or easily made at home. A homemade vibration sensor uses a small mass on a lever, which is activated by a switch to an alarm when it vibrates. Homemade motion sensors can work, but they can also be unreliable.

Other Motion Sensor Features

Wireless Motion Sensors:

Today, most motion sensors are wireless. Wireless sensors are very easy to set up. They do not require drilling, and they communicate with the other security system components wirelessly.

Contact Motion Sensors (door/window):

Most contact motion sensors are passive infrared sensors. They trigger an alarm if the protected door or window is opened while the system is armed.

Pet Immune Motion Sensors:

A passive infrared sensor can be set up to ignore animals up to a certain weight. A dual technology motion sensor is more resistant to false alarms caused by animals because it requires two sensors to be triggered in a manner determined by the manufacturer. They can be set up to ignore a large animal or multiple small animals without setting off a false alarm. Some pet immune motion sensors have a sensitivity level that can be adjusted for families with very active animals.

Video Motion Sensors:

Combines video cameras with advanced signal processing. Some record-able motion sensors start recording when they sense motion. Cameras controlled by motion sensors can save you memory storage by not recording hundreds of hours of useless footage—they only capture the important stuff.

24V VS 12V LED Light

There has different working voltages of LED lights, nowadays, LED strips are the most popular type of LED light driven by constant voltage LED driver, the general working voltage are 12V and 24V.

As for constant 24V and 12V LED light, the LED strip light driven by 24V power supply has longer permissible distances between light source than 12V LED light.

The difference of 24V LED light strip VS 12V one

The cut size: 24V type is almost twice longer than the 12V type. Based on the same power, you can cut the size of 12V LED strip with every 50mm, however, for 24V led strip light, you should cut every 100mm. So, the cutting length of 24V LED strip is twice longer.
The drop voltage: 24V LED strip performs better in drop voltage, which means the brightness from the very beginning to the end of the strip is almost the same.

In conclusion, 12V LED lights are ideal for lower wattage tapes, for example our 4.8W and 9.6W tapes both require a 12V LED power supply. This will give you full brightness along the LED strip, up to a length of approximately 6 meters from your 12V LED driver. (After 6m you will start to see a noticeable dip in brightness due to voltage drop. Beyond this length, you will require a second reel of 12V LED lights, to be wired back to the transformer in parallel.)

We supply our strips in standard 5 metre reels, as this is the optimum length. Or if you prefer, we can supply your 12V LED lights pre-cut to the lengths you need; cut-points for both 4.8W and 9.6W 12V LED lights are located every 50mm.

Any 14.4W or 19.2W LED tape needs to run at 24V. This is because the higher voltage will carry the current better, which is required to produce full brightness across the LED tape up to approx 6 metres. Again, these tapes are supplied in standard 5m reels but we can supply them pre-cut to the nearest cut-point. Cut-points on 14.4W 24V LED lights are every 100mm; the 19.2W tapes cut-points are every 50mm.

Types of LED Drivers

LED driver has two types: constant voltage led driver and constant current led driver, depending on whether they regulate output to provide a constant voltage or current to the LEDs. Constant voltage led driver can be called voltage converter or ac to dc transformer, due to it covert the AC high voltage to DC low voltage, which normally has 5v power supply,12v power supply, 24v power supply, 36v power supply and 48v power supply (variable dc power supply).LED driver is used for LED light, before we purchase any LED driver, you need know below main specifications:

Electrical parameters: Power, voltage and current, first, you need know the working voltage or current of LED light, then, you can check the output voltage and current of your led driver, do they match?

Dimming function, dimming type, if your led light is dimmable, you need check which dimming type is: 0-10v, dali, PWM signal or triac. Make sure your led driver has the same dimming type.

IP rate, waterproof or non-waterproof. Do you use the led driver in outdoor or indoor place? Is the place wet or dry? The IP rate can be IP20 (non-waterproof) to IP68 ( can be installed in water)

LED driver

waterproof led driver

Ac to dc converter: LED driver is a type of ac dc power, LEDs require a device that can transform incoming AC power to the proper DC voltage, and regulate the current flowing through the LED during operation. The LED driver & power supply converts 230V (or other voltage 110V) AC power to low-voltage DC power required by the LEDs, and protects the LEDs from line-voltage fluctuations.

There has some types of power supplies can be used for both traditional lights and LED lights, such as the switching power supply ( also known as switching-mode power supply, switch mode power supply, SMPS, or switcher) is an electronics power supply that incorporates a switching regulator to convert electrical power efficiently, which normally used for led strip lights today.

LED driver is the most important part for any LED system. You probably faced the situation that led driver power supply was broken but the LED was still good. As the rapid growing of led light during these years, there has many led driver manufacturers appear in the market, the quality and price is vary, how to find the best power supply for your LED lights among the different led drivers? Do you know the difference of constant current and constant voltage led driver or the information of wattage, power factor(PF), power factor correction (PFC), power efficiency, IP rate, housing shell,RoHS materials,electronic components,full load burn-in test,approval protection(over current, over load,short circuit and over temperature protection) ?

Read more information from LED Driver: The Definitive Guide

Find product list of LED power supplies

Power Factor Correction

Power Factor Correction (PFC) can be defined as the reduction of the harmonic content, and/or the aligning of the phase angle of incoming current so that it is in phase with the line voltage. Mathematically, Power Factor (PF) is equal to Real Power (Watts) divided by Apparent Power (Volt*Ampere). The basic concept is to make the input look like a pure resistor. Resistors have a power factor of 1 (unity). This allows the power distribution system to operate at maximum efficiency, which reduces energy consumption.

Non-PFC power supplies use a capacitive filter at the AC input. This results in rectification of the AC line, causes high peak currents at the crests of the AC voltage. These peak currents lead to excessive voltage drops in the wiring and imbalance problems in the three-phase power delivery system. The full energy potential of the AC line is not utilized. Nonlinear peak currents also distort output voltage and create harmonics.

PFC circuits are classified into two types: active and passive.

Passive PFC uses passive elements such as a ferrite core inductor on the input source to create a countering reactance. While easily applied to the existing power circuitry without much modification, the power factor is low (60 – 80%), the AC input must be chosen (115VAC / 230VAC), and the harmonics produced from the difference between the capacitance and the inductance are hard to control. Significant electromagnetic noise can result.

Active PFC uses switching regulator technology with active elements such as IC, FET and diodes, to create a PFC circuit This circuit has a theoretical power factor of over 95%, reduces total harmonics noticeably, and automatically adjusts for AC input voltage. However, it requires a complex EMI filter and an input source circuit, and is more costly to build.

The benefits of high PF for the user comes from the reduced AC current drawn by high PF PSUs, not in any savings from electricity bills, except in the case of commercial utility users who do pay for V(oltage) x A(mperes). There are two broad consequences:

Less stress on the AC electrical wiring: The lower current drawn by a high PF power supply means that there is less stress on the electrical wiring of the building. This can be a big plus in the case of older building with lower capacity AC wiring. It is certainly easy to see the benefits in a enterprise setting where dozens or hundreds of PCs are drawing power. If the total current load from the IT department could be reduced by 30% or more, this would be very signficant in direct electricity savings, reduced airconditioning cost, and possible avoidance of building AC re-wiring.

Lower UPS costs: Lower current draw also means that smaller capacity Uninterruptible Power Supply (UPS) units can be used. As UPS units are priced in direct proportion to their current capacity (VA), a PF of 0.98 versus one of 0.6 can traslate into a 40% reduction in purchase cost. Again, in an enterprise setting with hundreds or thousands of PCs, the savings can be very significant.

PFC Myths

There are myths about power factor correction that continue to be propagated by well-meaning people. Let’s tackle the two most common ones:

Does higher PF reduce my electricity bill? No, if you are a home user. If you are an enterprise running hundreds of PCs and pay not only for power but also VA, then yes. For more details, see PFC discussion above.

Does PFC make a power supply more efficient? Not in the normal way that power supply efficiency is defined, which is the power loss (to heat) as a percentage of total AC input in AC-to-DC conversion. However, in the sense that Apparent AC power (VA) is lowered, PFC does reduce energy consumption.

Power factor correction is applied by an input circuit which uses a small amount of input power. With two PSUs that are identical, equipping one with PFC will cause a typical efficiency drop of 2~4%. Many PSUs that have Active PFC also have high efficiency, as APFC is usually found on higher quality PSUs, but the two are not intrinsically related.

Safety Extra Low Voltage

What is SELV?

SELV stands for Safety Extra Low Voltage.

The safety of this system stems from its low voltage level, which should never exceed 50 V ac or 120 V dc, and is too low to cause enough current to flow to provide a lethal electric shock. Some AC-DC power supply installation manuals contain warnings concerning SELV. For example, there may be a warning about connecting two outputs in series because the resulting higher voltage may exceed the defined SELV safe level, which is less than or equal to 60VDC. In addition, there may be warnings about protecting the output terminals and other accessible conductors in the power supply with covers to prevent them from being touched by operating personnel or accidently shorted by a dropped tool, etc. The reason for the difference between ac and dc levels is shown in below:

It is not intended that people should make contact with conductors at this voltage; where live parts are not insulated or otherwise protected, they must be fed at the lower voltage level of 25 V ac or 60 V ripple-free dc although insulation may sometimes he necessary, for example to prevent short-circuits on high power batteries. To qualify as a separated extra-low voltage (SELV) system, an installation must comply with conditions which include:

– it must be impossible for the extra-low voltage source to come into contact with a low voltage system. It can be obtained from a safety isolating transformer, a suitable motor generator set, a battery, or an electronic power supply unit which is protected against the appearance of low voltage at its terminals,
– there must be no connection whatever between the live parts of the SELV system and earth or the protective system of low voltage circuits. The danger here is that the earthed metalwork of another system may rise to a high potential under fault conditions and be imported into the SELV system.
– there must be physical separation from the conductors of other systems, the segregation being the same as that required for circuits of different types.
– plugs and sockets must not be interchangeable with those of other systems; this requirement will prevent a SELV device being accidentally connected to a low voltage system,
– plugs and sockets must not have a protective connection (earth pin). This will prevent the mixing of SELV and FELV devices. Where the Electricity at Work Regulations 1989 apply, sockets must have an earth connection, so in this case appliances must be double insulated to class II so that they are fed by a two-core connection and no earth is required,
– luminaire support couplers with earthing provision must not be used.

Voltage Drop

Voltage drop describes how the supplied energy of a voltage source is reduced as electric current moves through the passive elements (elements that do not supply voltage) of an electrical circuit.

Whenever a current is flowing, the current will meet dynatron, which will impede its flow, the amount of voltage loss through the entirety of a circuit, or even a part is voltage drop. In low voltage lighting systems such as LED strip lights, voltage drops occur because the input voltage from the power supply gradually decreases over the length of the strip.

The longer the flexible led strip light is, the more resistance the current has to overcome; hence it loses voltage along the way. If the flexible LED strip light runs off a 12-volt power supply, then you have 12 volts going into the strip light system at the start but the other end will not have 12 volts due to the voltage drop.
Voltage drop is a function of wire length, wire thickness, and the total watts of power used by the flexible LED strip lights. A reduction of brightness and color accuracy in longer flexible LED strip lights is due to excessive voltage drop. The excessive voltage drop may result in unsatisfactory operation of, and damage to, electrical outlets and the flexible LED strip tape lights. The distance from the power source to the desired end distance of the flexible LED strip tape is called a run. Shorter and/or thicker wires will raise the brightness and color consistency to the strip lights’ full potential.

How much voltage drop is acceptable? A footnote (NEC 210-19 FPN No. 4) in the National Electrical Code states that a voltage drop of 5% at the furthest receptacle in a branch wiring circuit is acceptable for normal efficiency. In a 120 volt 15 ampere circuit, this means that there should be no more than a 6 volt drop (114 volts) at the furthest outlet when the circuit is fully loaded. It also means that the circuit has a resistance that does not exceed 0.4 ohms.

What are the consequences of “excess” voltage drop in a circuit? Excess voltage drop can cause the following conditions:

1. Low voltage to the equipment being powered, causing improper, erratic, or no operation – and damage to the equipment.

2. Poor efficiency and wasted energy.

3. Heating at a high resistance connection/splice may result in a fire at high ampere loads.

At what % voltage drop does a circuit become hazardous? It is difficult to say at what point excess voltage drop will cause a fire, because it depends on how much current is flowing through the high resistance connection, what is the resistance of that connection and because many factors must be considered regarding at what point ignition will occur, e.g.:

1. Is the high resistance connection in contact with a combustible material?

2. Is there air flow to dissipate the heat?

3. Is the area around the connection insulated, so that heat cannot escape.

RECOMMENDATIONS

For power efficiency, the NEC standard of 5% maximum voltage drop is recommended.

From a safety perspective, because wiring connections in some homes deteriorate with time (particularly in homes that use aluminum wiring for power circuits), and do-it-yourself modifications may be less than professional, excess voltage drop is a concern because of the potential fire hazard at high resistance connections, particularly on circuits that power electric motors while occupants of the dwelling are asleep, e.g. air conditioners, refrigerators, furnace fans, exhaust fans, etc.

Some agencies arbitrarily set a maximum voltage drop criteria of 10% to be considered unacceptable and a hazard. The author believes that any voltage drop difference of >1% from an adjacent receptacle should be investigated, that any voltage drop difference of >2% from an adjacent receptacle should be considered a hazard, and that using a maximum voltage drop criteria of more than 8% (3% above the “efficiency” recommendation) is courting disaster. A 3% voltage drop (3.6 volts in a 120 volt circuit) at one connection with a 15 ampere flow develops 54 watts of heat – which can cause ignition under certain conditions.