Lumejet to unveil photonic printers at Digital Print UK

By Simon Nias, Wednesday 09 January 2013

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Lumejet will unveil a new breed of digital printer later this year when it demonstrates its photonic printing technology at Digital Print UK at the NEC from 5-7 November.

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Lumejet's continuous tone S200 has an equivalent half-tone resolution of 8,000dpi

Lumejet, which was founded in 2010 and has since raised more than £4.5m from angel investors, has developed a printer that combines digital print techniques with analogue silver-halide based photographic media.

The Lumejet S200, which is the firm's first product, is an LED-based print system that uses a similar print technique to digital inkjet printers, except instead of ink, it "prints" light in dots that are just four microns across.

Lumejet claims that this device is capable of producting an equivalent half-tone resolution of 8,000dpi by exposing just 400dpi, because it give the same continuous-tone (contone) result as traditional analogue photograph printing.

According to the technology's inventor, Dr Trevor Elworthy, a former Kodak research scientist and now Lumejet director of innovation, the unique element of the Lumejet's design is a fibre tapered lens that is used to produce the micro dots that enable the Lumejet's ultra-high resolution.

This lens is the key element of a Lumejet printhead, which otherwise consists of an array of 300 commercially available 0.3mm LEDs per head, 100 each for red, green and blue light, in three rows.

"The innovative bit is the taper, which is comprised of millions of individual 20 micron fibres that have been heated and extruded to give a diameter at the narrow end of the taper of just 4 microns [per fibre]," said Elworthy.

"There is no fusing of the fibres during the extrusion process so there is no light scatter or bounce within the taper – what goes in at the top, comes out at the bottom as a series of coherent micron-sized LED spots."

The reason 4 microns was chosen as the base diameter of each fibre was because this is the approximately the size of the photo receptors in the media, so the Lumejet is capable of producing the maximum resolution within the limitations of the substrate.

This is said to solve the problem of light scatter in the media versus earlier photonic imaging technology, which used much larger spots, typically 60-80 micron. "Earlier systems were ok for smooth skin tones, but not very good at fine text and graphics requiring hard edges," said Elworthy. "You need the micro dots to get the edge definition."

Elworthy explained that the colour negative photo-sensitive media is silver-halide based and comprised of three principal layers, one on top of the other, each tuned to a particular wavelength of light (one each for R, G and B).

Each silver halide grain is surrounded by a large number of initially colourless dye globules (so called colour couplers), which - after exposure and development - turn into a complementary colour: the red grains produce cyan dyes; the green produce magenta; and the blue produce yellow.

The silver grains are bleached out and are recovered leaving just the three coloured layers as tiny micron-sized filter plates in direct proportion to the RGB exposure in each pixel.

This means that instead of printing CMYK dots side by side as in halftone printing, with the white substrate underneath giving a pseudo colour effect, each dot sits directly on top of the other, giving a continuous tone.

Elworthy added that Lumejet has none of the registration problems that can arise in half-tone printing as the alignment is done very accurately via electronic timing in the printhead, which places the RGB pixels at an accuracy of better than 0.1 micron.

In addition, because Lumejet processes in RGB rather than CMYK it has a much wider colour gamut without the need for spot colours and can more accurately render difficult colours, with a delta E of less than 0.7.

The amount of colour from each layer (RGB) governs the final colour of a particular dot; black is achieved by exposing a 100% dot on each layer and gives a deep black with a density of around 2.5.

Miles Bentley, commercial director at the 24-staff, Coventry-based start-up said that the device was aimed at the fine art and high-end photobook markets, as well as pitch books for architects, ad agencies and interior designers.

Because the Lumejet's print speed is slow relative to toner or inkjet based digital printers, but its resolution much higher, Bentley said it was ideal for short-run, high quality, print-on-demand applications of 1-100 copies where quality is paramount.

He added that the device was aimed at a different market to both the Durst Lambda, which was primarily used for POS applications, and the mainstream B2C photobook market, which is dominated by HP Indigo.

"We have no aspirations to take on HP Indigo," said Bentley. "Our aim is to have a beta site up in eight weeks and around 30 installs by Digital Print UK. We're targeting 1,000 units shipped in western Europe & US in the next four years."

The S200 is reel-fed and has 305mm print width with edge-to-edge detail and no bleed or trim, and therefore reduced waste. It has a 1m repeat length, which Bentley said was chosen to give it the ability to print A3 landscape lay-flat photobooks.

Its print speed is 40m/hr, equivalent to 250 A4 sheets/hr and its list price is £145,000. Bentley said consumables, including paper and chemicals, worked out at around 12p per A4 sheet. Lumejet is recommending Fujifilm media, but Bentley said the device would print on any silver halide-based substrate.


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