LED Lighting Knowledge

LED Strips SERIES and PARALLEL circuit connection guide

LED Strips SERIES and PARALLEL circuit connection guide

Basic LED principles:

An LED (light-emitting diode) is a semiconductor light source that emits light when current flows through it. Light is energy in the form of photons that emit when electrons in the semiconductor recombine with electron holes. 

The higher the current flow, the brighter the LED becomes. However, the circuit is not perfect and some of the current is converted to heat instead of light. When the current reaches a certain value, the heat generated is so high that the semiconductor is permanently damaged. In most LED data sheets, this important limit is specified as "Absolute Maximum Current".

Even if the LED operates below the maximum current, the heat will slowly damage the LED, causing its luminous flux (light output) to gradually decrease. The time when the LED luminous flux is only 70% of the initial value is commonly referred to as "LED life".

For LEDs to have a very long life of 50,000h or more, a current level well below the absolute maximum current is required, which is referred to as the "typical" or "recommended" current.       

Constant current source for the recommended current

To operate an LED at the recommended current requires an external circuit, a constant current source. Without it, the current in the LED increases exponentially with the applied voltage, as a small change in voltage results in a large change in current until the maximum current is reached and the LED burns out. 

The external circuit, constant current source can be a simple resistor for low power LEDs (max 100mA at 3V) or a stand-alone device called an LED driver

LED drivers come in many shapes, sizes and power levels and many accept 230 VAC input. Some dedicated LED drivers accept VDC inputs at higher levels than the output (buck converters) or lower levels (boost converters).

A common characteristic of LED drivers is that they provide a constant current output (CC out) within a voltage interval. This output voltage interval is specified in the LED driver data sheet. For example, an LED driver with 350mA CC output at 1-10V can safely power an LED if the voltage required for 350mA is within the 1-10V interval. Examples include a red LED 2V @ 350mA, a white LED 3V @ 350mA, or a COB LED 9V @ 350mA.

Theoretically, it is optimal to use one LED driver for each LED, an approach that is impractical from many points of view, for most LED types. Exceptions are the COB LEDs with very high power, from 50W upwards. 

Series and parallel electrical circuits

To light up a string or array of LEDs from one LED driver, the LEDs must be connected into an electrical circuit. This can be a series or a parallel circuit. 

We will explain these circuits with examples using our popular LinearZ 56 cm LED strips, with SunLike TRI-R CRI97+ LEDs, Nichia Optisolis CRI98+ LEDs or special Nichia Rsp0a Horticulture LEDs:

1. Series connection with LinearZ Sunlike CRI97+ LED strips:

One LinearZ 56 cm Toshiba-SSC LED Strip Zhaga Sunlike CRI97 warm white 2700K has the recommended current at 350mA, reached at the voltage of 39.5VDC.

A series circuit with two, three or four LinearZ LED strips is shown below:

LinearZ LED strip Series connection

The series connection is applied by connecting the positive (+) terminal of the first LED strip to the negative (-) terminal of the second LED strip. This pattern is repeated for further LED strips, from the negative (-) of the second strip to the positive (+) of the third strip and so on. At the same time, the negative (-) of the first LED strip is wired to the (+) of the second, then the (-) of the second to the (+) of the third and so on. 

In a series connection of LED strips, the current of the string is equal to the current of the first LED strip, while the voltage is the sum of the voltages for all LED strips (voltage of the first LED multiplied by the number of LED strips):

1 x LinearZ 56 cm Sunlike CRI97+ LED strip: 350mA at 39.5VDC

2 x LinearZ 56 cm Sunlike CRI97+ LED strips in series: 350mA at 79VDC (= 39.5VDC x 2)

3 x LinearZ 56 cm Sunlike CRI97+ LED strips in series: 350mA at 118.5VDC (= 39.5VDC x 3)

4 x LinearZ 56 cm Sunlike CRI97+ LED strips in series: 350mA at 158VDC (= 39.5VDC x 4)

2. Parallel connection with Nichia Rsp0a Horticulture LED strips:

The parallel circuit is applied by connecting the positive (+) of the first LED strip to the (+) of the second LED strip. This pattern is repeated for further LED strips, from the (+) of the second strip to the (+) of the third strip and so on.

At the same time the negative (-) of the first LED strip is wired to (-) of the second, then (-) of the second to (-) of the third and so on.

 

LED strips Parallel connection

In a parallel circuit of LED strips, the current of the string is the sum of all current values of the strips, while the voltage is equal with the one of the first LED strip:

1 x LinearZ 56 cm Nichia Rsp0a Horticulture LED strip: 350mA at 37.5VDC

2 x LinearZ 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 700mA(= 350mA x 2) at 37.5VDC

3 x LinearZ 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 1050mA(= 350mA x 3) at 37.5VDC

4 x LinearZ 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 1400mA(= 350mA x 4) at 37.5VDC

3. Combined circuit with LinearZ Nichia Optioslis LED strips

Series and parallel circuits can be combined, for example:

We create one group of two LinearZ Nichia Optioslis LED strips in series. Because one LED strip has 350mA at 39.5VDC, the group will have 350mA at 79VDC (= 39.5VDC x 2)

This group we connect in parallel to a second group, identical to the first (350mA at 79VDC). Then values of the string will be: 700mA (=350mA x 2) and 79VDC (=39.5V x 2).

Series and parallel connection

The above can apply for single LEDs also. On our LumiFlex700 Pro Toshiba-SSC LED Strip Sunlike CRI97, segments of 7 LEDs in series are daisy-chained in parallel for a total length of 5 meters. The total circuit requires a constant voltage driver of 24VDC.

 

4. Selecting the LED driver for a string of LED strips

Before selecting the LED driver the current and voltage value of the string of LED strips must be known and the type of input: constant current or constant voltage.

Examples:

1 x LinearZ 56 cm Sunlike CRI97+ LED strip: 350mA at 39.5VDC will require the constant current LED driver Mean Well LPC-20-350 with 350mA output at 9 > 48VDC. 

1 x PowerBar V3 LED Module Aluminium UV 365nm 12180mW 700mA at 44.4VDC can use a constant current LED driver Mean Well LCM-40 with 700mA output setting at 2 > 57VDC. 

2 x LinearZ 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 700mA(= 350mA x 2) at 37.5VDC can be connected to a constant current LED driver Mean Well LCM-40 with 700mA output setting at 2 > 57VDC. 

3 x LinearZ 56 cm Sunlike CRI97+ LED strips in parallel: 1050mA(= 350mA x 3) at 39.5VDC require a constant current LED driver Mean Well LCM-60 with 1050mA output setting at 2 > 57VDC. 

4 x LinearZ Nichia Optioslis LED strips in parallel: 1400mA(= 350mA x 4) at 39.5VDC need a constant current LED driver Mean Well LCM-60 with 1400mA output setting at 2 > 42VDC. 

5 meters of LumiFlex700 Pro Toshiba-SSC LED Strip Sunlike CRI97 function at 24VDC and have a total power consumption of 96W (=19.2W x 5). In this case we can use one constant voltage LED driver at 24V, such as HLG-150H-24B with 150W maximum output.

10 meters of LumiFlex350 Pro Samsung LED Strip CRI90 function at 24VDC and have a total power consumption of 126W (=12.6W x 5) can also work with the HLG-150H-24B.

 

Disclaimer:

This article is for informative purposes only. It is not a installation guide. LED strips our other electrical components should be installed by qualified personnel (such as an electrician). 

Recommended light levels for office lighting with LED systems

 Recommended light levels for office lighting

 

According to the standard EN 12464 Light and lighting - Lighting of workplaces -Indoor work places, the light level recommended for office work is the range 500 - 1000 lux - depending on activity. For precision and detailed works the light level may even approach 1500 - 2000 lux. For ambient lighting the minimum illuminance is 50 ulx for walls and 30 lux for ceilings.

Recommended light levels for different types of work spaces are indicated below:

Recommended light levels for different types of work spaces are indicated below:

Activity Illuminance
(lx, lumen/m2)
Areas with traffic and corridors - stairways, escalators - lifts - storage spaces 100
Working areas where visual tasks are only occasionally performed 100 - 150
Warehouses, archives, loading bays 150
Coffee break room, technical facilities, ball-mill areas, pulp plants, waiting rooms 200
Easy office work 250
Normal office work, PC work, show rooms, laboratories, check-out areas, kitchens, auditoriums 500
Mechanical workshops, office landscapes 750
Normal drawing work, detailed mechanical workshops, operation theaters 1000
Detailed drawing work, very detailed mechanical works, electronic workshops, testing and adjustments 1500 - 2000
Performance of visual tasks of low contrast  and very small size for prolonged periods of time 2000 - 5000
Performance of very prolonged and exacting visual tasks  5000 - 10000
Performance of very special visual tasks of extremely low contrast and small size 10000 - 20000

Read more about recommended lighting levels for the home in our blog article.

 

Flexible LED strips for applications with high lux requirement

Advice for the purchase and use of equipment for the UV disinfection of air and surfaces

Advice for the purchase and use of equipment for the UV disinfection of air and surfaces

This article is intended as a guide for those who are considering purchasing UVC disinfection equipment in 2021. These tips should only be considered as suggestions.

Attention buyers! - There are few recognized standards for equipment designed for UVC disinfection of air and/or surfaces. As a result, there are many advertisements and promotions claiming amazing performance with little or no scientific support.

  • Ask the seller for copies of scientific papers that prove that his device actually works as he claims. The scientific work(s) should show the actual reduction of a test micro-organism in the environment in which the device is intended to work. 
  • Does the product have suitable built-in UV safety sensors for automatic shutdown or does safe operation depend entirely on the operator?
  • Does the device comply with NIOSH, UL, IEEE and related safety standards in the country of sale?
  • Does the unit emit/generate ozone? If so, does it meet NIOSH requirements. How is the ozone attenuated? (We recommend avoiding ozone equipment, as it poses a safety risk to operators, unless ozone is specifically part of the treatment process and is used in a controlled and safe manner)?
  • Is the device used to disinfect medical devices? If so, is it compliant with the requirements of the regulatory body in the EU, USA or country of sale?
  • If the device is a UV rod that is used to disinfect a surface (e.g. a worktop or an envelope)

The technical specifications should state the UVC irradiance at a fixed distance from the UV front of the device (e.g. 10 mW/cm2 at 2 cm).

The UV dose (irradiance multiplied by exposure time in seconds) should be at least 20-40 mJ/cm2 to inactivate viruses on perfectly flat and ideal surfaces (details in this article). Thus, if the irradiance at the target surface is 10 mW/cm2, the exposure time should be 2-4 seconds. However, the presence of microscopic gaps on flat surfaces can inhibit disinfection, and disinfection on other materials, such as cloths, may require completely different doses. For example, disinfection of viruses on medical masks may require doses as high as 1000 mJ/cm2. This is a subject that is currently being researched and our current understanding changes almost daily.

With any UV device, you must NOT look at the UV light or expose your hands from the UV side. UV light is a source of skin burns/cancer and can quickly damage the eyes.

Remember that UV disinfection is based on a "line of sight" between the UV lamp and the target surface. If the UV rays are shaded by texture elements on the surface, the shaded areas may receive much less UV light or no light at all. Disinfection effectiveness is therefore determined by the UV dose to which these areas are exposed.

Like any disinfection system, UVC equipment must be used properly to be safe.

They all generate different amounts of UVC light in wavelengths from 200 - 280 nm. UVC light is much more energetic than normal sunlight and can cause a severe, sunburn-like reaction on your skin and could also damage the retina of your eye when exposed.
Some devices also produce ozone as part of their cycle, others produce light and heat like an arc welder, and still others move during their cycles. In general, all disinfection devices must therefore take into account the safety of both man and machine.

These considerations should be taken into account in the operating manual, in user training and in compliance with appropriate safety regulations.

UV Fluence (Dose) recommended for 90% or 99% disinfection from Viruses, Bacteria, Protozoa and Algae

UV Fluence (Dose) recommended for 90% or 99% disinfection from Viruses, Bacteria, Protozoa and Algae

 When designing, building or installing a UV light, two key questions must be answered first:

"How irradiance does it need to have?"

"What is the required exposure time?"

While there are many studies that show the effectiveness of UV light in disinfection or sterilization, a high variance of the results exists, which presents a challenge to find an answer to these questions. 

We will present our recommendations by analyzing the results of 413 reasearch papers, as found in the compilation "Fluence (UV Dose) Required for up to 99% disinfection from Viruses, Bacteria, Protozoa and Algae"  that can be downloaded at the links below:

PDF: Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae

The research studies present the fluence required to achieve a log reduction from 1 to 5, for different types of UV sources.

The effectiveness of sterilization or disinfection with UV light depends on the exposuretimewavelength and irradiance.

  • Exposure or fluence (sometimes called dose) is measured in mJ/cm2 (where 1 mJ/cm2 = 10 J/m2)
  • Exposure time is measured in seconds (s), minutes (m) or hours (h)
  • Irradiance is the flux of radiant energy per unit area, in other words how much of the UV radiation power (measured in W = 1000 “miliwatts” mW = 1.000.000,00 “microwatts” μW ) reaches the surface. Irradiance is measured in mW/cmor W/m2 (1 mW/cm2 = 10 W/m2) and is dependent on the radiant power, distance and dispersion of the radiation emitted by the lamp source.

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Disinfection with UV Light can deliver 99% Kill Rate for Bacteria and Viruses (incl COVID-19)

UV light breaks the DNA of viruses and bacteria

Effective and cost efficient disinfection or sterilizing of surfaces, water and objects can have a significant, positive effect on the general health of our society. The impact of pandemics, present such of the COVID-19 (coronavirus), and future can be greatly reduced, as well as a major decrease of illnesses in general, including from drug resistant pathogens or hospital-acquired infections (HAI).

Disinfection or sterilization with ultraviolet (UV) light can be the way to achieve such goals. However, challenges of using UV light still exist and the ways to overcome them are presented in this article.

"UV light annihilates viruses and bacteria by destroying their ability to reproduce. "

Using ultraviolet (UV) light to disinfect or sterilize1 has actually been embraced by some hospitals since years, by using large, industrial-grade machines to kill microorganisms (including COVID-19) in hospital rooms or on furniture, objects, clothing or instruments. However, such machines are the perfect showcase of the challenges of using UV light. They are prohibitively expensive for private or business use, as a mobile platform with UV lamps can cost more than 60.000 USD2. Their deep UV radiation is also dangerous for people and must be used only in empty rooms.

UV robot for hospital use

With the current advances in UV LED lighting technology both problems can be overcome.

Smaller versions of UV disinfection lamps can be built at affordable cost, so they are accessible to consumers and companies looking to clean pretty much everything, from office spaces, elevators and living rooms, to phones, computers and even toilet seats.

Different UV wavelengths with precise control of intensity and radiation pattern can make disinfection safe to be used when people are present.

The most promising practical application of the above is the continuous disinfection with low intensity UVA LEDs .

"Continuous disinfection: UVA radiation functioning for 8 hours, daily. Safe for people*. Will kill up to 99% of viruses and bacteria**. "

*Irradiance limited to 10W/m2 at 2m from the floor.

**According to two independent studies quoted in this article.

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Recommended color rendering index CRI base on your project

The CRI, colour rendering index, is a one-number quantification that indicates the performance of an artificial light source in terms of colour rendering compared to a reference standard light source modelled on daylight. The highest number is 100, for daylight and incandescent/halogen lamps, while gas discharge lamps range from 17 to 96, with even a negative value for low sodium pressure (the yellow type used in street lamps).

Due to this variation in the ability to reproduce colour with the white light emitted by the many types of gas lamps on the market, CRI index was introduced in 1974 by the International Commission on Illumination (CIE). 

Today, with more than 40 years of use, the CRI index is firmly rooted in the lighting industry and among professionals. However, it has not been very well understood by the public. The reason was that such knowledge was not really useful as most lamps were built for specific applications that required a minimum CRI value, so one could not go wrong when choosing a lamp.

For example, for office or other linear lighting, the lamps of choice where Tri-Phospor linear fluorescent tubes on the market since the 1970s, all with a CRI value above 80. For domestic lighting, there was a mix between incandescent and halogen lamps, both with CRI100, for retail and other high intensity spot lighting, metal halide lamps with CRI min 85. Street lighting was reserved for high intensity and very efficient sodium vapour lamps, which had a poor CRI but this was considered not important.

From the year 2000 this changed with LED technology, the first light source that can be used for any application while having a broad performance and quality level, including the ability to reproduce colours accurately. It is therefore essential that you choose LEDs with the right CRI level for your application.

CRI comparison

The picture above shows how colors can look different based on the CRI of the light source that illuminates them. A vibrant red under sunlight or a high CRI light can look dull or even orange under a low CRI light.

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Tips on how to build the best lines of light or linear light fixtures with LED strips

Lines of light are a new trend in lighting design and are usually made with an LED strip inside an aluminum profile that has a translucent white cover. The attraction of using such a linear light fixture is that it can be personalized. You can choose as you desire the pattern, place of installation, length (up to many meters), geometric shape or a combination of these elements.  

Line of Light with LED strip inside a profileBecause of their way of construction lines of light are a type of direct lighting. Compared with coves that are indirect lighting, lines of light are more energy efficient but can have greatly increased glare. For this reason lines of light should be designed with care and almost always be dimmable. 

Let's see how we can achieve the best results with lines of light.

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Tips on how to have the best illuminated stretch ceiling with LED modules

The illuminated ceiling or stretch ceiling is very interesting trend in interior lighting. By using a translucent material many square meters in size with a backlighting system, a diffuse, even and relaxing illumination of interiors can be created. The main advantage of this type of lighting is the absence of glare, as the light sources are distributed over a large area and hidden behind the material.

The backlight source is usually low or medium brightness LEDs (5 to 50 lumens) mounted on strips or modules. Since the illuminated surface has a large area, such low power illumination is the best choice.

Illuminated stretch ceiling with LEDs, inside an office

Illuminated stretch ceilings can have personalized shapes and even feature translucent images. They can therefore influence the overall design of a room much more than other lighting fixtures. From a lighting design perspective, uniform light should be supplemented by spotlights or lamps that can draw attention to specific areas or objects.

The proper design and installation of a luminous ceiling has a number of unique challenges that we will address in this article.

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Cove lighting with LED strips: HOW TO

A Cove light is a line of light can obtained via a LED strip hidden from view inside a cove in the wall or ceiling that illuminates an adjacent surface. Light is reflected from this surface into the space that has to be illuminated. That is why lines of light are commonly known as cove or indirect lighting.

Cove lighting is beneficial trend to design lighting, with focus on human nature and how natural light behaves. It is today widely adopted, with lines of light as a principal way to illuminate interiors.

The allure is the similarity with natural light. With the proper light source used, we could imagine that the cove is actually a hidden window to the outside from where sunlight flows in.

Lets explore how we can have the best results with cove lighting

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What does IP wateproof rating means and what value are recommended IP levels for the bathroom

WHAT DOES IP PROTECTION MEAN?

The IP protection index is an essential feature of most electrical equipments and indicates the degree of protection of the device against external factors such as solid objects or liquids. This protection is expressed by the word "IP", followed by 2 numbers that indicate

  • The first digit describes the degree of protection against solid objects, dust, solid particles and bodies
  • The second digit describes the degree of protection against liquids

The IP rating is relevant when the environmental conditions are standard; in special cases and hazardous environments, special protection is required.


Although there are numerous combinations of IP ratings for LED strips, the most common are IP67, IP65, IP44, IP20. In general, all LED strips have IP20 protection,  IP44 can be found for LED strips within an aluminium profile with closed end caps and IP65 or more is normally used for waterproof LED strips.

The first digit – protection from foreign bodies

  • 0 – no protection from foreign bodies;
  • 1 – protected against solid objects greater than 50mm(e.g. accidental touch by hands);
  • 2 – protected against solid objects up to 12mm(e.g. fingers);
  • 3 – protected against solid objects greater than 2.5mm(e.g. tools and wires);
  • 4 – protected against solid objects greater than 1mm(e.g. small tools and wires);
  • 5 – protected against dust, limited ingress(e.g. no harmful deposit);
  • 6 – totally protected against dust.

The second digit – protection from liquids

  • 0 – no protection from liquids;
  • 1 – protection against vertically falling drops of water(e.g. condensation);
  • 2 – protection against direct sprays of water up to 15 degrees from vertical;
  • 3 – protection against direct sprays of water up to 60 degrees from vertical;
  • 4 – protection against water sprayed from all directions – limited ingress permitted;
  • 5 – protected against low pressure jets of water from all directions – limited ingress permitted;
  • 6 – protected against high pressure jets of water (use on ship deck) – limited ingress permitted;
  • 7 – protected against the effects of immersion between 15cm and 1m;
  • 8 – protected against long periods of immersion under pressure.

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