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LED UV lamps, technologies and use: Frequently asked questions

Everything (or almost everything) you have to know about UV LED

UV LEDs are currently the technological leap in the sector­of UV sources.

The benefits are described in other pages of the site.

The user interested however needs to be informed as completely ­­as possible on the new technology, and any doubt should be clarified.­

On this page we provide the answers to questions that commonly arise there.

The questions are divided by topic for easier understanding of the informations:

GENERAL FEATURES

When and where you use the UV LED lamps ?
UV LED lamps are used when it is necessary to cure (or dry/harden) products such as inks, paints and resins used in industrial processes where it is necessary to achieve high productivity. These products dry very quickly if irradiated by intense UV rays emitted from LED lamps.

In what industrial processes can be used UV LED lamps ?
They can be used in many industrial processes including:

  • Screen printing, flexographic printing, pad printing.
  • Digital printing Ink-Jet.
  • Industrial UV coating.
  • Grouting and UV resin filling.
  • Structural bonding with adhesives and UV resins.
  • Industrial marking by ink-jet.
  • Medical and pharmaceutical
  • Wood finishing

UV LED lamps can ever used instead of traditional UV lamps ?
UV LEDs are often used successfully in place of traditional UV lamps, but is not always possible to use them because of the chemical formulations of products which may not be fully compatible with the radiation emitted from UV LED lamps.

How do behave inks / coatings formulated to traditional UV lamps if used with UV LED ones ?
Products formulated to be used with traditional UV lamps contain mixtures of photoinitiators tuned to the frequencies of Mercury UV lamps. UV LED lamps emit more selective frequencies that may not completely cure the products developed for traditional UV lamps. It is often necessary contact the manufacturer or the dealer for more information and possibly perform compatibility tests.

How to choose UV LED lamp that best suits your needs ?
UV Led­lamp should be chosen based on three main characteristics:

  • Radiation working width: maximum width in millimeters that the lamp can radiate and dry
  • Peak irradiance: maximum irradiance expressed in W/cm2 that the lamp is capable to emit at a certain distance from the emission window
  • UV dose: quantity of Energy emitted in the time available, expressed in mJ/cm².
  • Frequency: frequency peak of the spectrum emitted, expressed in nm (nanometers). Since UV LED lamps have a spectrum very narrow and selective, the spectrum emitted is considered as a single frequency

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IRRADIANCE AND UV DOSE

What emission power rates are available ?
There are UV lamps with same size LED window but with different maximum radiated power to better adapt to the needs of industrial UV curing. The maximum value is­ ­16W/cm2 .

What emission frequencies are available ?
There are two main emission frequencies: 365nm or 395nm. 385 and 405nm radiations are also available on request.

What power and frequency is the most suitable for my application UV ?
The irradiance and the frequency most suitable for your application depends primarily on the product
that must polymerize and in addition the distance between the surface and the lamp and the translation speed under the lamp.

What distance have I to keep between the UV lamp and the LED surface to polymerize ?
UV LED lamps are kept close enough to the surface to polymerize. For lamps with ­­Flat Window­ ­optical system,­the working distance is between 1 and 15mm, whereas for lamps with ­Focused Lens­­ optical system,­the working distance increases and it is between­ ­10 and 25mm. For lamps with ROD lens optical system, the working distance is between 1 and 25mm. ­Distances are always measured from the front glass which emits UV radiation.

What happens if the distance between the lamp and the surface to be dried is too high ?
The product to be polymerized may be uncured properly due to an insufficient energy peak, which does not complete the chemical reaction.

How can be dried irregular and no-planar surfaces with UV LED ?
Using UV LED lamps of the DROLED series­ you can distance the emitting window­ from surface to be polymerized and still obtain a high radiant energy. Through Focused lens optical system, the light that comes out is focused and it permits of consume less energy when the distance increases.

UV LED lamps degrade and have a drop in performance during their life ?
Yes, also UV LED lamps have a slight performance during their lifetime although very limited when compared with traditional UV lamps. The drop is about 10% at the achievement of 20,000 operating hours at full power.

After reaching 20,000 working hours what happens? The lamp stops working ?
No, lamp will continue to operate beyond 20,000 hours. The energy emitted will be about 10% less than a new lamp. In most cases this decay of performance does not involve the replacement of the lamp.

Could frequent starts and stops reduce UV LED lamps lifetime ?
No, contrary to traditional UV lamp, frequent on/off switchings don’t reduce the duration of UV LED lamp.

Could frequent starts and stops help increase the duration lamps ?
Yes, the switching on and off of UV LED lamps extends the lamp’s life, because during the off period the emitting diodes do not work and consequently do not degrade.

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DIMENSIONS AND MECHANICS

What size have UV LED lamps ?
Lamps are available in various sizes to best suit the application. Refer to the data sheets for further information about available dimensions.

What is the radiation width ?
It is ‘the maximum width that the UV LED lamp is able to irradiate and polymerize homogeneously.

What it means by “module” of a lamp composed of several modules ?
The “module” is the base width unit that lamps are made of­.

If a lamp module is used more than others, is it possible to replace it when exhausted ?
Yes, but it can be done by technical assistance only.

If I have to dry 220mm width, what is more convenient: to use three lamps one module type (80mm) or buy one lamp only 3 modules type (3 x 80mm) ?
Economically you should buy a three modules lamp type, but using­ modules of 80mm it is possible separate them phisically and use them in a differerent way.

How can I radiate large widths and dry correctly ?
It is possible to irradiate large width alongside one another more UV LED lamps,­ getting so a large­ radiant width and always homogeneous over the entire length.

How lamps can mechanically be fixed ?
You must use threaded holes present on the metal casing which are dedicated for mechanical fixing and clamping over printing machines.

What main precautions should I consider during mechanical installation ?
Always should be considered that lamps can work in air-cooled ambient temperatures not above 45°C and then outgoing and incoming air flows have not­to be obstructed or covered .

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POWER AND CONTROL

How are electrically powered lamps ?
They are supplied by standard switching AC/DC­ ­power supplies available in the market with many sizes and models.

How power supply has to be dimensioned ?
The UV LED lamp manual contains the informations about how to dimension each lamp model.

Can UV Led lamps be controlled­by using a PLC ?
Of course. You can do it through direct analog and digital signals or through RS485 serial protocol .

How can functions be controlled in easy mode ?
Through analog and digital signals it is possible to:­turn lamp on / off, adjust the intensity,­verify the lamp status and the presence of anomalies .

How can functions be controlled ­in advanced mode ?
Through a 2-wire RS485 serial link, it is possible to control and query ­the lamp functions or group of lamps in advanced mode, following the owner communication register available on the manual.

What does the “Interlock” command serve­?
It is used to connect a safety circuit (such as a limit switch actuated by a barrier). Interlock command has the priority over all other commands

Command Interlock can be excluded ?
Yes,­ it can be by-passed by a connection bridge between two taps.

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OPERATING

Con quale strumento posso verificare l’irradianza emessa dalla lampada ?

What instrument is necessary to check the irradiance emitted by the lamp?
A special UV-meter suitable for measuring UV LED sources.
More exactly:

  • By an UV Meter (called also UV Radiometer) is measured the UV intensity, value expressed in mW/cm².
  • By an UV Integrator (called also UV Dosimeter) is measured total amount of UV radiation during the exposure under UV Led lamp, value expressed in mjoule/cm².

How UV Led lamps are cooled ?
All Photo Electronics UV Led lamps of the DROLED series are cooled by forced air through an built-in integrated system.

WARRANTY AND SUPPORT

What happens in case of a malfunction ?
The internal electronic microprocessor intelligently monitors constantly lamp parameters, and if necessary, it stops the lamp operating, preventing failures.

How may I realize that the lamp is not working properly ?
A digital signal of alarm activates, and some Led signals, visible from ventilation slots flash.

How is it possible to know the cause of a malfunction ?
It is possible find the majority of causes through the LED signals flash number, which corresponds to error codes reported in the manual, or by downloading the file LOG, if expected by the lamp model.­.

What should I do if UV Led lamp is defective ?
In some cases the malfunction can be corrected by yourself without the necessity of open the lamp, while in other cases you might have to send it back for repair.

Lamps have a warranty period ?
The warranty is provided in accordance with local­law.

How can I protect myself in case of accidental breakage of the lamp ?
It is possible to enter into a contract for a quick lamp replacement (temporary spare lamp).

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MAINTENANCE

What maintenance do lamps need ?
The only maintenance interventions are: the cleaning of the emission glass window ­and of the air filters .

How can I clean the lamp if it gets dirty ?
Debris and scales over the glass can be removed mechanically or by using some solvents.

Some lamp type is provided with inlet air filter.­How can I clean the air filters ?
Using a jet of compressed air. If they are very dirty, they ­­must be removed from the holder and­ ­washed with water and a bit of ­detergent.­Then dry them. Never use other liquid and/or solvents.

How often have I to clean the filter ?
Depends on the conditions of working enviroment, on average every 2000 hours.

What happens if I don’t clean the filters ?
If filters get dirty, this reduces the air flow. Lamp might stop automatically, signaling a malfunction.

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