IT should have been an ordinary day like any other. But Saturday 15 August 1998 will never be forgotten. On that summer afternoon, at 3.10pm, a car bomb exploded on Omagh's Market Street, killing 31 people, including unborn twins, and seriously injuring hundreds more. The worst single incident of the Troubles, it left the Co Tyrone town reeling with unimaginable grief and trauma, and the wider community, north and south, utterly horrified.

This Friday marks the 10th anniversary of the Omagh bombing. A commemorative ceremony will be held on the day, during which a Garden of Light memorial, incorporating the site of the bombing and a nearby garden, will be unveiled.

Unfortunately, the memorial has been dogged by controversy. The Omagh Support and Self-Help Group, which represents many victims' families and is campaigning to have an international inquiry established to investigate the bombing, voiced concerns about the wording of an inscription in the garden: they wanted to ensure it said the victims were murdered and injured by a "dissident republican terrorist bomb".

An independent facilitator was brought in and, after some 80 meetings, an agreement was finally reached that the support group's favoured narrative would feature in the garden itself, while less contentious language would be used for inscriptions at the site of the bombing and on a wall leading to the garden.

However, Friday's official service will still be boycotted by some members of the support group, who will hold their own service on the Sunday closest to the anniversary, as they do every year.

The wording on the plaque was not the only difficulty faced by those seeking to create a permanent tribute. When the competition to design the memorial was announced, the brief was particularly challenging – not only because of the practical requirement to link the site on Market Street with the garden some 300m away, but also because of its seemingly contradictory aims. "We must move forward in a positive and progressive manner," it stated, "but all the while remembering the atrocity inflicted and the carnage suffered. To this end we need to be reflective and reverential but positive, optimistic and forward looking."

Such a desire encapsulates the inherent dilemma of memorialisation. How can a memorial adequately address the scale of the tragedy, while not simply focusing on the trauma and suffering? How can it present hope for the future, while at the same time acting as a reminder of the lives lost and pain caused, and taking into account the ongoing suffering of survivors and victims' families?

The winning design, by Newry-born artist Seán Hillen and Dublin architect Desmond Fitzgerald, attempts to reconcile these divergent concerns. It is a project of immense technological complexity and ambition, but with an accessible, universal aesthetic. The central theme is that "light unites us all in that it makes all life possible", and the aim is to use sunlight to link the two sites.

The site of the explosion will be marked by a 4.5m glass obelisk with a cut crystal heart suspended inside it. Around the corner, in the memorial garden, a large mirror, known as a heliostat, will track the sun and, whenever it shines, pour beams of light onto 31 pole-mounted mirrors. The light is then reflected onto a mirror on a nearby street corner and bounced, finally, onto the floating crystal heart of the pillar, which will sparkle and glitter whenever the light reaches it.

According to Hillen, the aim was to demonstrate humanity at its best, both through the technological ambitiousness of the project, and through the focus on our capacity for love. "I thought I would represent the enormity of the tragedy by showing what humans are capable of at their best rather than their worst, because we saw what they were capable of at their worst," he says. "So I've put a heart symbol at that spot… It means the core of things, the most important part, but it's also a universal symbol of compassion."

Hillen hopes people will draw strength from the fleeting moments of sunshine that will illuminate the glass heart on Market Street. "Omagh has the lowest level of sunshine of anywhere in Ireland," he says. "And that added to the irony and poetic truth – that the sun isn't going to shine all the time, and that's one of the sad truths of life, but we hope it will shine again."

Eimear McKeith