To power 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.

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We create one group of two LumiBar 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)

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In order for LEDs to have a very long lifetime, 50.000h or more, a current level far below the Absolute maximum current is required, referred to as "typical" or "recommended current".

The colour of the paper may be due to its being dyed during manufacture, or the colour may be applied to it by a process something like printing, in which case it will be coloured on only one side. This is known as surface-coloured paper or "white back."

The principles above can also apply for single LEDs. On our LumiFlex3098+ Pro Toshiba-SSC LED Strip Sunlike CRI98, 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.

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).

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

Lithographed stamps are printed from an absolutely flat surface so that the ink of the design lies smoothly on the surface of the stamp, the characteristics of stamps printed by this method being a flat, smooth appearance.

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.

LED drivers are available in many shapes, sizes and power levels and many accept 230 VAC input. Some specialty LED drivers accept VDC input of higher levels than the output (step-down converters) or lower level (step-up converters).

Laid paper, when held up to the light, shows parallel lines of greater or less width running across the stamp. Russia provides any owner of a general collection with examples of stamps on both types of laid paper. Other classes of paper sometimes met with include pelure paper, the official definition of which is "a very thin, semi-transparent paper, about the thickness of tissue paper, but much harder and tougher."

In the paper on which some stamps are printed, there is a watermark. This consists of a device formed in the texture of the paper itself and can be usually seen when the stamp is held up to the light. If the watermark cannot be seen in this way, it will probably show up when the stamp is placed face downwards on the black polished surface of a watermark detector.

Chalk-surfaced paper or coated paper belongs to the latter class, as any attempt at cleaning brings away the preparation with which the paper is coated, at once altering the appearance of the stamp. A test for chalk-surfaced paper is to touch slightly the surface of the stamp with the edge of a silver coin.

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

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There is the paper on which it is printed, the design, by which we usually mean the pictorial part of the stamp, the inscriptions, or lettering and figures of value, the ink with which the design is printed, varying in colour, the gum, and the means of separation i.e. the perforation.

Granite paper has tiny specks of coloured fibre in it, which can usually be seen with the naked eye. Some quite common stamps of Switzerland, the issue of 1882-98, furnish a good example of this paper, though they were also printed on wove paper.

One LumiBar 56 cm Toshiba-SSC LED Strip Zhaga Sunlike CRI98 warm white 2700K has the recommended current at 350mA, reached at the voltage of 39.5VDC.

Many of the earlier French and French Colonial stamps have the colour only on the surface, in this way, while the "white backs" of some of the British Colonies are familiar to most collectors.

3 x LumiBar 56 cm Sunlike CRI98+ 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.

Typography stamps or surface printed stamps are those stamps printed from the raised portions of the type or printing plate. It is these portions which represent the design of the stamp and which receive the ink during its transfer onto paper. The pressure used during the printing tends to indent the design into the paper.

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 mentioned in the LED driver datasheet. For example, a LED driver with 350mA CC output at 1-10V is able to safely power one LED under the condition that its voltage required for 350mA is within the 1-10V interval. Examples include a red LED 2V @ 350mA, white LED 3V @ 350mA or COB LED 9V @ 350mA.

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

Apart from unintentional variations from mixing it, it may be affected by the amount of moisture in the atmosphere during printing or drying or by the temperature of the air-- variations in these other aspects give rise to variations in colour, which are called "shades" by philatelists.

Where the spacing varies on different sides of the same stamp, the perforations are said to be compound. Opposite sides usually have the same spacing, so that when you read "Perf. 15x14" you will know that the first figure given is the gauge of the top and bottom of the stamp, while the second is that of the left and right sides. The figure for top and bottom always comes first.

5 meters of LumiFlex3098+ Pro Toshiba-SSC LED Strip Sunlike CRI98 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.

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2 x LumiBar 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.

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. For example:

Some method was, therefore, necessary for indicating the arrangement of the holes, and as these were usually spaced regularly, it was decided that the number of holes in a space of two centimetres should indicate the perforation of a given side of a stamp. Thus the description "Perf. 15" does not mean that there are 15 perforations on every side of a stamp, for naturally, the longer side would have the most holes, but that, in any space of two centimetres on any side of the stamp, you will count 15 holes.

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We will explain the two types of circuits with examples using our popular LumiBar 56 cm LED strips, with SunLike TRI-R CRI98+ LEDs, Nichia Optisolis CRI99+ LEDs or special Nichia Rsp0a Horticulture LEDs:

The surface of the paper is often specially prepared, sometimes with the object of getting a good surface on which to print, at others to prevent postmarks being cleaned from used stamps, so that they may be used again.

4 x LumiBar 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.

Thus one catalogue will describe the colour of a certain stamp by one name, while another will give a totally different description. Description in print is not of great assistance, but the Colour Guide is as helpful as anything at present available to the collector, as it shows 100 different standard colours or shades, and names them in a way that comes near to meeting general acceptance.

A wove paper has an even texture without any particular distinguishing features, as a very large portion of the existing postage stamps are printed on paper belonging to this class.

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1 x LumiBar 56 cm Sunlike CRI98+ LED strip: 350mA at 39.5VDC will require the constant current LED driver Mean Well LPC-20-350 with 350mA output at 9 > 48VDC.

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.

In a series circuit of LED strips, the current of the string is equal with the current of the first LED strip while the voltage is the sum of voltages for all the LED strips (voltage of the first LED multipled by the number of LED strips). For example:

Line-engraved stamps, recess-plate printing or printing from intaglio plates, as the third process is variously called, is the reverse of surface printing. The design is cut into the plate while the ink lies in these cuts, into which the paper is forced during printing, to pick up the ink. The design is this raised on the surface of the stamp and the lines of ink can often be seen standing up in minute ridges.

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Theoretically the optimum setup is to use one LED driver for each LED, an approach that is unpractical from many points of view, for most LED types. Exceptions are the very high power COB LEDs, from 50W up.

The term "shade" also requires explanation. A stamp is printed with the fixed intention that, so far as is possible, every copy of it shall be in exactly the same colour and in the same depth of that colour. But printer's ink is curiously wayward stuff.

A 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 beam out when electrons in the semiconductor recombine with electron holes.

A perforation gauge very soon enables the collector to tell the correct description of the perforation of any particular stamp. Successive spaces of two centimetres are divided by dots which exactly fit the holes on the side of the stamp whose perforation you are measuring.

The characteristics of the ink used in printing the design are not likely to trouble the ordinary collector, but its colour is important. The colours in which stamps are printed often cause confusion to collectors, chiefly because there is no recognised system of naming them, even if we could be sure that any two collectors see the same colour alike.

The series circuit is laid out by connecting the positive (+) of the first LED strip to the negative (-) of the second LED strip. This pattern is repeated for more LED strips, from the negative (-) of the second strip to the positive (+) of the third strip and so on. At the same time, negative (-) of the first LED strip is wired to  (+) of the second, then (-) of the second to (+) of the third and continuing.

The higher the current flow, the brighter the LED becomes. However, the circuit is not perfect and a part of the current is converted into heat instead of light. When current reaches a certain level, the resulted heat is so high that the semiconductor is damaged permanently. Most LED datasheets mention this important threshold as "Absolute maximum current".

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Early stamps were issued in sheets in which no provision was made for easily separating stamps. Scissors had to be resorted to. Then came the perforating machine, whose pins produced regular lines of holes between the stamps, so that their separation was easy.

Even when the LED is functioning at below the maximum current, heat will slowly damage the LED, its luminous flux (light output) gradually diminishing as a result. The point in time when the LED luminous flux is only 70% of its initial value is generally referred to as "LED lifetime".

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To power an LED with the recommended current an external circuit is required, a constant current source. Without it, the current in the LED will rise exponentially with the applied voltage, as a small change in voltage leads to a large change in current, until the maximum current is reached and the LED burns up.

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).

Single watermarks are often arranged so that one device falls on each stamp in a sheet. There are cases where they are placed close together so that parts of more than one watermark fall on each stamp and those are known as multiple watermarks.

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 continuing.

But the arrangement and spacing of the holes were not always similar, even in stamps of the same issue, and as such differences usually proved the use of a new or altered perforation machine, they came to be of interest to collectors, as they often helped to fix the date or period when particular stamps were issued.

There have also been instances where paper prepared for printing sheets of a certain size of a stamp has been used for stamps larger or smaller in which case the watermark will fall irregularly. There are often watermarks, usually consisting of inscriptions, on the marginal paper surrounding the sheet of stamps and those are known as marginal watermarks.