UV LED Technology

During the last years, UV LED market is significantly growing thanks to power and efficiency, to increasing wave lengths absorbed by ink, varnish, glues photo-initiators.

UV LED technology is the solution of the future for the UV curing processes for applications as UV drying of glues and coating (i.e. on wood, metal, resins,  electronics …), inks in graphics industry (digital printing, flexo, serigraphic) or special treatment as glass printing or automotive industry.

Applications of UV LED technology

The main applications UV LED technology are:

  • Graphic industry/screen Printing drying
  • Wood, Metal, Glass – Coat drying
  • Disinfection for food, cosmetic, pharmaceutic industry
  • Label, resins, glue polymerization

General characteristics of UV curing system using UV LED technology

The main parts of a UV curing system using UV LED technology are:

  • UV LED lamp
  • PSU (power supply unit)
  • Interconnect cable (to connect LED lamp to PSU)

Optionally the following items can be included:

  • Liquid chiller (manage circuit for water cooling  for lamp power > 4-8 W/cm2)
  • Interlock box (temperature sensor + protection circuit to switch off the LED lamp in case of over temperature alarm)

The UV LED lamps have a very selective emission peak, centered on precise wavelengths (365, 385, 395, 405 nm), in fact there are emission in UV-B and UV-C range (see figure below )


LED (single) chip size can be a fraction of mm^2 to several mm^2 (thickness<100 micron), this implies LED module scalability e flexibility in terms of shape and size.

Single LED chip are mounted on PCB using a complex wire bonding process; in addition in case of N LED module, 2N wire bonds are needed on PCB, as consequence, generated heat is really high. For this reason it is important to use an efficient chilling technique. Unlike to UV lamp ignition phase, LED module switches on instantly when low voltage /current is applied. Generally a LED chip works in voltage/current range 2-4 V 20-200mA, its UV irradiance is directly proportional to the amount of current  passing through the device. If this amount of current is too high LED chip can be seriously damaged; to balance the current flow through LED chip (and so the light emission), constant-current drivers and PWM technology are used. The use of constant current driver enables individual LED chips to be traversed by continuous (non-fluctuating) currents (when powered). For application requiring different power levels, PWM techniques is used to generate different output power levels (varying duty cycle %). PWM techniques is based on instant answer of LED diode, switching really quickly from ON state to OFF state. Max irradiance (peak value) is always the same for all power level, the ON interval is changed according to needed power level. For each LED module, there is DRIVER BOARD that:

  • distributes DC voltage to LED chips
  • provides constant current
  • implements PWM functionality

The driver board can be integrated to LED module or to PSU. Generally LED module integration is better because diode electrical noise is minimized and interconnect cables sized is reduced.

The key factors to consider in choosing or designing UV LED system are:

  • Peak-to-peak λ

Note: LED output is monochrome and UV light intensity depends on wavelength (for instance: λ=365nm I=2W/cm2 – λ=395nm I=10-16W/cm2)

  • max UV light intensity
  • UV LED matrix size
  • distance between LED module and surface to be treated has to be considered: this distance depends on application and, generally, is in the range 5 – 15 mm.
  • LED array Duty Cycle with PWM, to be adapted to production line speed, to optimize energy density (UV intensity x exposure time).

Advantages of UV LED technology, comparing with UV lamps

The main advantages of UV LED technology, comparing with UV lamps, are:

  • Power saving (40% power consumption less  than UV lamp)
  • Low environmental impact (no mercury usage and no ozone production)
  • No reflection optical systems , shutters, etc. needed
  • Deterioration Reduction of the mechanical parts and of material aging (no UV-B emission)
  • Power consumption = 0 W during OFF period
  • Istantaneous ON-OFF switching
  • Reduction of heating on surface to be treated
  • LED system flexibility due to LED modularity
  • UV efficiency = 25-30% (versus 10-15% for UV lamp)
  • LED lifetime = 20,000 hours (versus 1000-2000 hours for UV lamp)
  • During LED lifetime, LED UV decreasing less than 10% (see below picture)