1. Types

According to their purpose, with some degree of conventionality, all LEDs can be divided into two groups:

  • indicator;
  • lighting.

According to their design features, modern diodes are divided into 3 types: pin, SMD (Surface Mount Device) and COB (Chip On Board). Plus, LED filaments are also singled out separately. These are diodes that are primarily used in original light bulbs that imitate traditional models with incandescent filaments. We will not dwell on this type in detail, but we will examine the other three groups in more detail, because they are noticeably more universal.

Filament lamps with LEDs that imitate incandescent filaments.

Lead-out diodes

Long metal contacts extending from the semiconductor crystal (chip) are a characteristic feature of pin diodes. Thanks to the "legs", the diode can be easily soldered to the printed circuit board and provide hidden installation - with only the luminous lens exposed.

The main application for output diodes remains indication. But many chips have sufficient power and brightness for use in lighting devices. They are found in garlands, laser pointers, levels, household and automotive lamps.

Depending on the shape of the lens, output diodes are divided into 3 subgroups:

  • Round. They provide different head diameters - most often 3, 5 or 8 mm. Smaller products (3 and 5 mm) are used for indication, and larger ones - for lighting, including in advertising signs.
  • Cylindrical. They differ from round diodes both in shape and in a fairly high intensity of glow. They also come in different diameters - from 3 to 8 mm.
  • Rectangular. This lens shape simplifies installation. A special type of these diodes are products of the Piranha LED type. They have 4 contacts instead of two, which improves heat dissipation, vibration resistance and overall reliability. These products are actively used in automotive lighting, including turn signals, taillights, etc.

Various types of pin diodes, including piranhas - in the center with four legs.

By the standards of modern LED technologies, output diodes are not considered the brightest and most energy efficient. But they are also cheaper than their competitors.

SMD LEDs

The next step in evolution is Surface Mount Device (SMD) diodes, i.e. surface-mounted chips. Here, a semiconductor crystal (one or more) is placed directly on a printed circuit board and can have different sizes (3.5, 5 mm wide, etc.). Small contact strips are used instead of large pins. There is also a substrate that provides heat dissipation, increases the stability of operation and the overall durability of the diode. The role of the lens is usually performed by a phosphor, but a focusing plastic shell can also be used to provide a directional light flux in powerful models.

SMD diodes are widely used today. They are used for indication and lighting - both auxiliary lighting and main light. They are present in most household lamps, LED strips, etc. Due to various assemblies based on SMD diodes, it is possible to provide lighting devices with the required luminous flux (brightness) and other technical parameters. At the same time, each element (chip) has its own contacts on the microcircuit, which allows you to include different crystals in the assembly - blue, green, red. As a result, it is possible to implement multi-color lighting, i.e. RGB, and also provide flexible adjustments of color temperature.

SMD diode with three crystals and 6 contacts.

SMD LEDs can be noticeably brighter than pin LEDs. They are superior in reliability and energy efficiency, but are more expensive.

COB LEDs

COB technology, or Chip on Board, also involves placing crystals on a printed circuit board. But in this case, several diodes are “soldered” onto a common substrate and covered with a single layer of phosphor. The COB array is close in its implementation to the assembly of SMD diodes, but is distinguished by an increased density of crystals per unit area, and this in practice provides the following advantages:

  • more uniform illumination (the array looks like a single LED panel, not a multitude of miniature bulbs);
  • increased total brightness;
  • increased energy efficiency due to high-quality heat dissipation.

The difference between a COB diode and an SMD assembly.

COB technology assumes the presence of a single electric circuit with two contacts. As a result, within one array, as a rule, identical crystals are used and there is no possibility of changing either the glow palette or the color temperature.

COB diodes are used in various lighting devices, including lamps, chandeliers, LED strips, lanterns, etc. At the same time, their high brightness and energy efficiency are best demonstrated in the following scenarios:

  • to create intense light, for example, in spotlights, auxiliary lighting lamps;
  • in large spaces, commercial properties and open areas;
  • in automotive lighting systems.

For a clear comparison of the main types of LEDs, we have summarized their key features in a table:

Comparison parameter Lead diodes SMD COB
Main area of application indication and backlight lighting lighting
Brightness low high the highest
Color and color temperature can be changed can be changed can't be changed
Homogeneity of glow low average high
Energy efficiency average high the highest
Overall reliability average high high
Price minimal average medium and high
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2. Technical parameters

In addition to taking into account the type of LEDs when choosing different lighting devices, it is worth paying attention to their technical parameters. The main characteristics include the following:

  1. Light flux. The indicator characterizes the brightness of the diodes and largely determines the coverage of space and range (but here it is also important to take into account the scattering angle). Light flux is measured in lumens, the higher the value, the brighter the light. In practice, both an insufficient and clearly excessive indicator can become a problem if the lighting device does not have additional adjustments.
  2. Power. This is a parameter that determines the amount of energy expended per unit of time. Diodes are often divided into 3 groups - low-power (up to 0.5 W), medium (up to 3 W) and powerful (from 3 W). The efficiency and brightness depend on the power. But the latter parameter is also affected by the type of LED. For example, SMD can produce a luminous flux of 50 lumens per 1 W, and COB - from 80 lm. And output diodes have much more modest capabilities, but they are still higher than tech of incandescent lamps. We remind you that a 5 W LED bulb shines like a traditional 40-watt model.
  3. Color temperature. This indicator determines the comfort of perception and the appropriate scope of application of diodes. Thus, warm light corresponds to indicators up to 3000 Kelvin (K): such a color temperature promotes relaxation - suitable for bedrooms, catering establishments, etc. Neutral glow is a range from 3000 to 6000 K, which is considered optimal for workspaces, offices, classrooms, supermarkets. High values more than 6000 K mean cold white light, which promotes concentration and focus. This color temperature is optimal for galleries, operating rooms and other commercial facilities.
  4. Working life. This indicator is also called the degradation period. It determines the durability of the diode under proper operation and is usually indicated in thousands of hours.
  5. Diode dimensions. The overall sizes of the lighting fixture and the specifics of installation directly depend on it.
  6. Scattering angle. This parameter characterizes the spectrum of the illuminated space and is usually in the range of 100 to 120 degrees for diodes. Such angles correspond to directional glow. To expand the light flux, diffusers or assemblies of multidirectional diodes can be used, and special lenses can be used for focusing.
  7. Glow color. According to this parameter, monochromatic and multi-colored (RGB) diodes are distinguished. To obtain different shades, crystals of three colors are needed - blue, green and red, and special controllers are needed to adjust the palette.

Light bulbs with different color temperatures.

Other parameters that may be significant, for example, when assembling LED strips or other lighting devices yourself, include current and voltage. The search filter of additional equipment - resistors and drivers - directly depends on them. In addition, there is a direct communication between the operating voltage and the color of the crystal. So, if the voltage for a white chip is from 2.7 to 4.3 V, then for a red one - from 1.5 to 2.6 V.

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3. Top brands

Below are the market leaders and most reputable LED manufacturers:

  • Cree. A leading global brand from the USA, producing reliable, durable and high-quality products.
  • Osram is a German company that produces both LEDs and end products – household lighting fixtures and automotive lighting.
  • Luminus. Another American brand that guarantees high quality and offers a wide range of LED products in different price segments.
  • Lumileds. A Dutch manufacturer renowned for its advanced quality control technologies. This company is the main supplier of LEDs for the Philips brand.
  • Nichia. A Japanese company whose products are notable for their benchmark temperature stability and light uniformity. It is one of the TOP-3 best manufacturers of automotive lighting in the world.

Cree diodes are as popular as iPhones in the smartphone market.

Does a buyer of lighting fixtures need to know the top manufacturers of LEDs and understand this issue? Not always. Firstly, you can simply opt for reputable brands of the same bulbs or lamps - Eglo, Philips, Osram. They most often provide detailed technical characteristics of their products and are generally well regarded by users.

Secondly, if you choose a lighting device, and its main parameters (brightness, power, color temperature, working resource) are given on the label or on the official website, then the name of the manufacturer of the diodes themselves is also not mandatory information. It is needed here only by technical geeks.

But in all other situations, data on the LED brand is very valuable and useful. If this information is known, then we have an additional factor of trust in the product. Plus, the diode manufacturer can often give an idea of the overall reliability of the product. Thus, top brands guarantee up to 50 thousand hours of operation for their chips.

Important! Even with all the desire to consider the manufacturers of diodes before buying lighting devices, it is not always possible. This information is indicated less and less often lately. But it is necessary to remember that the Osram company uses its chips, and, for example, Philips closely cooperates with Lumileds. And in general, information about the diode brand is another weighty argument in favor of a particular product. So, if you compare two flashlights and one says that it is tried on by Cree, Nichia or Luminus, and for the second - there is no data, then the first model, without a doubt, looks preferable.
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4. Marking

The marking of diodes can provide additional information about these products in particular and lighting devices in general. So, if the manufacturer of a conventional light bulb specifies the power, color temperature and other parameters, then it is not necessary to delve into the nuances. But if there are gaps, then the ability to decipher the marking will allow them to be eliminated.

SMD diodes use specific markings, which indicate the product dimensions and other information. Let's look at the example of SMD 5050 UWC 5, where:

  • SMD is a type of diode;
  • 5050 is a standard dimensions that means the sizes in width and length are 5 by 5 mm;
  • UWC — Ultra White Color, i.e. white tint of glow (cold). Instead of UWC, just color can be indicated (for example, Green or other characteristics — UV — ultraviolet light);
  • 5 — power 0.5 W.

Colored diodes may also have the CRI parameter, i.e. the color rendering index, as well as other symbols indicating, for example, the date, manufacturer, etc.

There are no clear marking rules for COB diodes. Although you can find such a type of product designation as COB-3W-5000K-110Lm, where:

  • COB — diode type;
  • 3W — power;
  • 5000K — color temperature;
  • 110Lm — luminous flux.

Top manufacturers use their own designations. Let's look at several options in a little more detail.

Cree Marking

Cree offers a wide range of diodes and divides them into lines:

  • XP-E and XP-E2 are two series of chips of medium brightness (luminous flux from 250 lm) in a compact form factor. Such products are often used in budget flashlights. The number 2 denotes the second generation of the line with a point upgrade of operational properties. As a rule, the luminous flux is slightly higher and the energy consumption is lower than that of XP-E;
  • XP-G and XP-G2 are lines that also combine medium-brightness diodes (about 300 lm);
  • MC-E is a series of high-brightness chips (up to 900 lm). These LEDs are considered the next step in the development of XP-E and XP-E2;
  • XP-L is a line of bright chips (over 1000 lm) in a compact form factor;
  • XM-L, XM-L2 — series of high-power diodes with a luminous flux of over 1000 lm. Used in bright lighting devices and top-end flashlights.

Cree has a large assortment and many different lines of diodes.

All Cree output diodes represent three large families P4, PLCC and STD with numerous series. There is no point in listing them all. The important thing is that the line is always included in the marking. Also, the diode designation indicates the group (or bin), which affects the brightness of a specific chip. An example of Cree diode marking is XM-L2 U2, where:

  • XM-L2 is an updated version of the XM-L series;
  • U2 — bin — one of the brightest — only U3 is brighter. Cree has slightly less bright groups from T2 to T6, and S-ki are rated even lower.

Optionally, a color temperature code can be specified after the bin. For example, 1A is cool white, and 4C is neutral.

It should also be noted that within the XHP series, instead of a bin, the markings feature numeric designations that refer to the case sizes. Thus, XHP35 means a diode of the XHP series with sizes of 3.5 by 3.5 mm.

Luminus marking

Luminus also offers a wide range of products and many lines of LEDs. For example, let's consider two markings for different types of products - SMD and COB.

How to decipher the designation SST-40-WxS :

  • the first letter S is the SMD diode type;
  • the second S means a dome lens (there is also F - flat and other form factors);
  • T — symbolizes the presence of one emitter;
  • 40 — light radiation zone (indicated in mm²);
  • Wx — white color (White) without temperature indication;
  • S is the CRI category code, i.e. the color rendering index, in this case CRI>65.

Often you will see shortened markings such as SST-40 or SST-20.

There are many varieties of COB diodes in the Luminus line.

For Luminus COB arrays, you can find the following diode designation: CXM-9-30-90-36-PC32-F4-3 or the short form CXM-9, where:

  • CXM is a COB type;
  • 9 — size of the light-emitting surface in mm;
  • 30 — color temperature designation — 3000 K;
  • 90 — color rendering index, CRI not less than 90;
  • 36 — voltage 3.6 V;
  • PC32 — basic configuration;
  • F4-3 — bins, subgroups reflecting the brightness level (in this case from 1155 lm).
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5. What can you learn about a diode from its appearance?

The appearance can provide basic information about LEDs. In most cases, the type is even visually clear - pin-type LEDs can be easily distinguished from brighter and more advanced analogues. A single SMD diode is usually smaller than a COB array. The latter's module can vary in dimensions from 1 to 15 cm, and its shape can be round, oval, or non-standard, while SMDs are much more often rectangular.

An assembly of several SMDs is close in dimensions to a COB array, but provides for many contact groups, while the latter often have only two contacts. Plus, when turning on the light, you can easily evaluate the homogeneity and uniformity, which is worse for SMDs than for a Chip on Board array.

SMD2835 dimensions: appearance and sizes of the diode.

Want even more information? Measure the width and length of the SMD diode with a ruler or caliper. If you get the most common sizes, you can guess the approximate data on the luminous flux and the number of crystals using the table below:

Dimensions, mm Number of crystals Luminous flux, lm
3.5x2.8 1 5 – 7
5x5 3 or 4 18 – 20
5.6x3 1 58
5.7x3 1 or 2 50 / 158
3x1.4 1 9 – 13
2.8x3.5 1 20/50/100

It is impossible to determine the power or other data by the dimensions of the COB arrays. One can only assume that larger modules have higher power, although diodes of 1, 3 or 5 W are often visually identical.

Thank you for reading! We hope you found our quick guide to LEDs helpful.