When asked for this interview, Paul Keogan's reaction was one of complete astonishment: "Why on Earth?" He explains: "I'm not really sure how much people are aware of what I do." Audiences may not be aware of him but Keogan is everywhere. Having recently designed the lights for Opera Ireland's hugely successful productions of Lady Macbeth of Mtsensk and Madame Butterfly, he is presently working on Moliere's Tartuffe, in a version by Declan Hughes, at the Abbey. There are three jobs lined up after that. He works regularly with companies such as Bedrock and Loose Cannon as well as lighting a host of theatre and contemporary dance pieces along with an outdoor projection project in Kilkenny. He is one of the most prominent and creative lighting designers working in Ireland today. "In the words of Ronan Keating," he remarks dryly, "life is a roller-coaster." So, how is his job seen? "There's a perceived wisdom that the way a lighting designer works is you come in at the 11th hour, you see a couple of run-throughs, then you go away, do your design and it's `see you at the tech, luvvies'."

According to Keogan, the worst thing a director can say to him is "Just do your own thing . . . Turn them on, point them in the right direction and while you're up there put a few pretty colours in." The key-word, for Keogan, is collaboration. "I like to be part of the process from an early part of rehearsals right through to the production stages," he says.

Keogan has worked consistently with various companies over the years, developing ongoing relationships with directors such as Jimmy Fay, Jason Byrne, Brian Brady and Lynne Parker. With influences as diverse as Derek Jarman's film Chroma and Dorothy Cross's Nissan Art Project for Dun Laoghaire harbour, Ghost Ship (his minor degree is in History in Art), Keogan is eclectic in his interests and influences. He admits to "scant formal training as a lighting designer". He was studying drama at the Samuel Beckett centre when he was first introduced to semiotics and the potential of signals on the stage. "When you realise the semiotic possibilities of lighting - how it can help people focus in on a particular thing, trying to guide an audience's eye through the stage and round the action - it's another layer of interpretation."

Contemporary art is obviously a huge influence on his work. He credits his time spent as production manager at the Project ("If the Beckett Centre was university then the time I spent at the Project was my Masters") for having given him experience of lighting exhibitions, installations and talking with artists. With its strong sense of atmosphere and his characteristic use of side-lights, Keogan's design often seems as concerned with sculpting full bodies as lighting faces - a style that has not always found favour with conservative critics. I suggest that Keogan's early work lighting dance-shows has left its mark. "If I do have a style, the work I've done with dance companies probably has informed that to a large degree, because with dance you can afford to be bolder, can afford to let the lighting have a presence."

Perhaps it's because of this wide and varied background that Keogan is such an original designer and so unafraid to go against lighting orthodoxy. He is as willing to experiment with dark and shadow as with light itself.

"A lot of lighting designers get very concerned about the elimination of shadows," he explains. "But shadows are there, why not use them?" He adds, not without gentle self-mockery: "Darkness can be your friend."

In Bedrock's incredible Quay West, the manipulation of the dark was fundamental to the whole piece. With actors lurking in the shadows sometimes before, sometimes behind an increasingly jumpy audience, the effect of murky shadows severed by spell-binding shafts and pools of light not only created a unique psychological atmosphere but gave the piece the feeling of a happening, immersing the audience completely in another world.

It was the result of months of collaboration between Keogan, set designer Johanna Connor and director Jimmy Fay. For this show, Keogan earned his Irish Times/ESB Irish Theatre Award this year - somewhat ironically in light of the savage reviews the piece received from, among others, The Irish Times. It is still a sore point.

"It was a labour of love for all concerned. A lot of hard work went into it. I think the show was flawed, we all made mistakes - but I felt it was very, very harshly criticised by the press and it left a really bad taste in our mouths."

He does not believe that Irish audiences in general are mainly focused on the literary end of theatre. "I think that's quite patronising to the Irish audience. Cinema-going is alive and well and happening in Dublin. People are visually literate through television. We're probably getting more and more visually literate through the Internet and multi-media. While theatrically there's a very strong literary tradition, I think there's also a very strong visual tradition."

He mentions Operating Theatre - "extraordinary stuff - some of the best lighting design I ever saw," and the early shows of Patrick Mason and Joe Vanek, "extraordinary, groundbreaking productions".

Keogan himself recently worked with Joe Vanek, who he describes as "an absolutely brilliant designer" on Opera Ireland's Lady Macbeth of Mtsensk. It is a show of which he is particularly proud. The process was, again, a collaborative one, with Keogan involved at the outset. Together, Vanek and Keogan were inspired by a book of Russian film posters, "very constructivist, big strong blocks of colour", to create a unified vision of set and lighting, Russian in feel, dramatic in intensity. "The music took it. The music is very direct and in your face - big, loud, brassy, driving music. . . We looked at Expressionist theatre and the way they weren't afraid to be very strong in their colour choice. It's great if you can do that. Because I love saturated colour on stage." He familiarised himself with the music as he would read a play-script, playing it over until he could replay it in his head, before letting its character and movement inspire him.

"The final scene, if you hear it, it is the most glorious music, it starts very, very quiet and just grows and grows and you cannot but be inspired by that. It would be rude not to put a cue in there."

It strikes me the way that Keogan talks about his lighting has musical overtones: the lighting "counter-points" or else is "in sympathy" with a scene, snap cues "punctuate", slow fades "grow". He admits he sees it like underscoring a film - an additional layer, "a layer of interpretation" as he calls it. Sometimes this can be narrative, sometimes something altogether more visceral, sometimes an entire subtext can be suggested by the mood of the lighting "counter-pointing" a scene.

For most of us, however, this remains in the realm of the subconscious. "Some people would think I'm a glorified electrician," he remarks laconically. "It doesn't really bother me."

Does he see himself as an artist?

He pauses. "I suppose I do, yeah."

Then more definitely, "I do."

Tartuffe opens at the Abbey on Wednesday and runs until February 3rd