It all began on Australia Day in 1998, in front of 30,000 fans, when musician Paul Kelly performed and the Clarry Conners-trained Vitrinite, ridden by Shane Dye, became the first horse to score under lights. Dye also rode the John Morish-trained Stella Cadente to victory in the then-group 1 Australia Stakes.

Most of Victoria's major races are still run in daylight hours save for the Valley, which has made a marketing point of difference out of its floodlit fixtures and runs most of its big group1 and group2 races at night.

But it has so far had to stick to tradition with its greatest race, the Cox Plate, which is still staged during the afternoon.

However, even that is progressively being staged later so as to segue into the early evening television schedules of free-to-air broadcaster Channel Seven.

The Valley is happy with its position as the pre-eminent night-racing venue - the others are Cranbourne and Pakenham - and it will showcase its attractions tonight with a 20th-anniversary commemoration meeting, at which the group2 Australia Stakes will be the highlight.

The biggest impact of the mini revolution ushered in by the Valley's changes two decades ago has been on racing's protagonists - trainers, stable staff and jockeys, with the latter bearing the brunt of a changed working regime.

Matthew Hyland, the head of the Victorian Jockeys Association, said in the 2014-15 season Victoria staged 36 night meetings. Last season it staged 57 - more than 50per cent extra.

Jockeys, who need to be up early to ride trackwork and fulfil stable obligations at an afternoon meeting, may then be required to double up at twilight or night meetings - meaning their working day can stretch to 20 hours.

"We understand that the industry is maximising revenue and seeking the best opportunities to promote the sport. More sport is moving to night fixturing and racing is no different," Hyland said.

"But it has placed enormous strain on jockeys and those in the industry. If a rider has a young family with school-age children, it's quite possible that he may not see them for a day or two if he is up to ride trackwork or jump-outs at an afternoon meeting in the country and then has to go to Pakenham, Cranbourne or the Valley for a night meeting.

"We are not complaining because that is the way things are going, but it does take a toll."

Apprentices are restricted in the number of meetings they can ride in and can't take mounts at a day and night meeting. But senior jockeys (anyone who has come out of his or her apprenticeship) can.

Hyland said while it was up to them how they run their business (they are self-employed and can do as much or as little as they want) it was not that straightforward.

Jockeys get race rides from trainers if they ride trackwork or at jump-outs, so if they decide to miss out on early morning assignments to save their energy for race riding during the day and night, they are likely to find their opportunities drying up.

"It is relentless, and if you don't turn up there is always someone else who is prepared to jump on the wheel," Hyland said.

In many industries staff get penalty rates or extra benefits for working late or unsocial hours, but racing is different: riders get the same fee if they are competing in a race at 2.30pm or 9.45pm. Still, there are big rewards for those who are successful. A winner is a winner, no matter the hour, and the Australia Stakes, with a $200,000 purse, is worth winning.

It is the first "big race" of the year in Victoria and top sprinters often use it as a springboard to a lucrative autumn campaign. Last year it was won by the Ben Melham-partnered Malaguerra in a track-record equalling time of 1.09.29. Black Heart Bart finished second before going on to claim the CF Orr Stakes at group1 level.

Black Caviar took the race twice, in 2010 and 2012, while other big-name winners were champion sprinters Hareeba and Schillachi, and Cox Plate hero El Segundo.