FAQQuestions are there tobe answered

Questions are part of the routine, particularly with technical innovations which are numerous in the area of LED technology. As are the right answers.  An overview of the most frequent questions and answers is available here. For more information, please contact your assigned customer advisor.

LED technology in general

The higher the temperature, the shorter the service life. Heat management is a decisive factor in the design of the LED and the module.

The operating temperature is critical for the lifespan of LEDs. The following applies as a basic principle: The cooler the better. With regard to the thermal design of an LED light/system in particular, it should be ensured that all LEDs of an allocation are exposed to the same operating temperature. tc point stands for “casing temperature”. This describes the point on the LED of the device, which is usually hottest. It is applied to the circuit board and allows information about the behaviour of the LED. The tc point should be kept as low as possible. Reducing the temperature of the tc point from 80 °C to 60 °C increases the expected lifespan by 19,000 hours and the brightness by 6 percent.

The colour representation index (Ra) provides information about how natural colours are represented in the light of an LED. The lower the value, the poorer the colour representation. Ra values above 80 indicate good to very good colour representation properties.

The R1 – R15 values are specified, standardised test colours, which are used as references for measuring the CRI or Ra values. The average of these 15 reference colours is the Ra or CRI value. R9 is important because it is the value with the largest proportion of red and this value is used most frequently by end consumers.

The human eye tolerates colour deviations very differently, depending on the colour. The so-called MacAdam ellipses are used to classify LEDs, in particular with regard to colour location. They represent elliptical colour spaces (x and y coordinates), in which we do not yet perceive deviations from the reference. The MacAdam-Ellipse of stage 3 (SDCM3) represents the colour consistency (colour binning), which is possible through the close grouping of LEDs. This deviation is already so small that it can no longer be perceived with the naked eye.

In lighting technology, nanometres refer to the nano-layers of semi-conductor, which are mounted on the light-emitting diodes.

The method for determining the luminosity flux drop of an LED light source according to Standard LM-80-08 was published by the IESNA Solid State Lighting (SSL) Subcommittee in the third quarter of 2008. This document contains the measurement procedure for determining luminosity flux drop for inorganic LED-based light sources, arrays and modules. It does not contain any other aspects relating to LED properties. One of the reasons for developing LM-80-08 is the different procedures and criteria for determining LED properties. LED manufacturers typically measure with a short pulse without additional heat dissipation. This pulse is very short and is between 10 and 20 ms. The LED is measured in an almost cold state. As a result, no heat dissipation is needed and the temperature tj at the pn transfer corresponds to the ambient temperature ta (this value is usually stated as 25 °C). This procedure is necessary in order to measure very many LEDs in a short period. This explains why the datasheets of LED manufacturers usually state LED properties at tj = 25 °C.

A LED essentially consists of the LED chip, a contact to the cathode and anode and a plastic lens. The light-emitting diode consists of two layers of semiconductor material. One layer has an excess of electrons (n-layer). The second is the so-called p-layer. If these two layers are brought together, the charge differences in the same Boundary layer off. There is no current flowing, the n-p body is neutral. If a voltage is now applied, the current flow is started. The energy contained is released in the form of light.

Around 70 percent of energy is converted to light and 30 percent to heat.

Flexible printed circuit boards

FPC stands for Flexible Printed Circuit Board.

In principle, all chemical processes of circuit board production are possible, in which “soft” cutting takes place on the circuit board. This is the case with chemical tin, chemical nickel-gold (ENIG), chemical silver and OSP (Organic Surface Protection). The HAL (Hot Air Levelling) surface is not possible. Temperatures and compressed air in this procedure would damage the flexible circuit board.

Polyimide (PI) is a thermoplastic for high-temperature applications. It is very dimensionally stable, has a very high dielectric strength and as an adhesive-free film substrate is also high-frequency tolerant.

The maximum continuous operating temperature for adhesive-free polyimide-flex circuit boards is approx. 200 °C. Flexible circuit boards with adhesive have a maximum operating temperature of approx. 100 °C.

Polyimide or polyester is usually used. Polyimide is the higher quality solution here. With regard to temperature resistance, dielectric strength and dimensional stability, polyimide clearly performs better than polyester (PET). A cost-effective and high-performance intermediate solution is polyimide with adhesive. The drawback compared to considerably more expensive, pure polyimide lies primarily in thermal stability.

Parallel conductor tracks should be offset against each other on the top and bottom of double-sided flexible circuit boards. Apart from the offset positioning, right angles should be avoided. They generate sharp edges and could lead to the copper lifting if the flexible circuit board is loaded at this point. Tear-drops are planned for all pads.

Tear-drops are angled reinforcements in the conductor track shortly before the pads. They prevent abrupt edge formation. Right-angled edges are thus avoided, because otherwise tears could occur here in the copper when bending the flexible circuits.

Apart from the thickness of the material, the number of layers affects the flexibility of the circuit boards. The more layers, the more rigid the circuit board. Additionally, the thickness of the copper plays a decisive role. There are procedures, therefore, which etch the copper more thinly at certain flex areas so that flexibility is increased here.

In principle, a distinction is made here between adhesive-free flex material and flex circuit boards with adhesive. For adhesive-free circuit boards with polyimide film, the tg is roughly 220 °C. For flexible circuit boards with adhesive, the tg is only approx. 130 °C. This is because the adhesive is an epoxy resin and therefore has similar thermal properties to FCB.

The tracking resistance calculates the insulation resistance of surface materials. Standardised test conditions define the maximum tracking, in particular when subject to dirt and moisture. This tracking resistance of circuit board materials is defined in CTI values. The CTI value of flexible circuit boards is more than 100.

The dielectric strength of polyimide flex circuit boards is 100 to 240 kV/mm.

The dielectric constant, also called dielectric conductivity or dielectric function, indicates how porous a material is to electric fields. The dielectric constant of adhesive-free polyimide circuit boards is approx. 3.4 (at room temperature).


The thermal expansion coefficient of the BILTON LED modules is 17 * 10-6 K

With regard to profiles and covers, it must be noted that aluminium and plastic have different expansion coefficients, which must be considered during assembly. Starting at 20 °C, the length of aluminium profiles changes by approx. 0.25 mm per metre and for plastic by approx. 0.7 mm per metre for every 10 °C change in temperature.

Soldering may only be performed at the envisaged solder points “+/-” with a maximum temperature of 230 °C. Only lead-free solder may be used. So that no damage is caused, the soldering iron may only touch the solder points for max. 10 seconds. The bend radius should be at least 2 cm because the electronics are damaged if overloaded.


  • There must not be any mechanical load on the components of the flexible conductor foil.
  • The LED modules must not be operated when rolled up.


  • The conductor tracks must not be damaged or interrupted as a result of assembly.
  • Only suitable power packs should be used for operation. In addition, the following safety measures should be ensured: Short circuit protection, overload protection, SELVequivalent.
  • Check the poles are correct during commissioning. Otherwise the module may be damaged.
  • Strictly observe the maximum cable lengths.
  • Avoid electrostatic discharges.


  • BILTON LED dimmers must not be used with other loads.
  • The specified maximum values must not be exceeded.
  • Do not install LED dimmers directly next to heat sources and ensure sufficient air circulation (minimum distance: 20 cm).
  • Connected lamps must be designed for the maximum current.
  • Accessibility to operation and replacement of the device must be ensured.
Shortcut Describtion


Operating temperature


Ambient temperature


Storage temperature


Reference temperature


Processing temperature




Softening temperature


Organic Surface Protection: This describes a procedure, in which the surface of a material is protected when soldering circuit boards.


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