The websites and social media accounts of 24 festivals including T in the Park, Bestival, Lovebox, Global Gathering and Sonisphere will go dark for a day from 9am.
Music fans visiting the homepages of the participating festivals will be met with a completely black window except for a grey light bulb and the message "Don't be in the Dark about Legal Highs".
Blackout organiser the Association of Independent Festivals (AIF) said its members had banned the sale of legal highs by traders onsite at their events.
It comes after Home Office minister Norman Baker warned authorities are involved in a "race with chemists" in India and China who are producing potentially dangerous new legal highs on a weekly basis.
AIF's co-founder and vice-chairman, Ben Turner, said, "Legal highs are a serious concern for any festival organiser and the issue is only going to get bigger.
"The substances have managed to fly under the radar purely by evolving faster than the monitoring bodies can regulate.
"Banning it at our festivals is only part of the battle however, we need to make fans aware of the dangers of legal highs and help them make safer choices when having fun on-site."
AIF said festivals backing the blackout have a combined capacity of more than half a million people and an online reach well into the millions. It hopes to make the blackout an annual event.
It is working with Angelus Foundation, a charity set up to educate people about the risks of legal highs.
Angelus founder Maryon Stewart added: "Legal highs are a huge but hidden problem because young people are acting in ignorance and no-one is measuring the harms.
"As the lead organisation raising awareness of these substances, Angelus is delighted the festivals are taking the issue seriously and helping to keep their audiences safe.
"We are determined to keep expanding our prevention programme into new areas and bigger events until everyone gets the message that the effects of these substances are unpredictable and high risk."
Norman Baker said this week that the Government was examining the way the problem of legal highs was dealt with in other countries, including New Zealand where substances are set to be banned unless trials prove they are safe.
The Liberal Democrat minister said the Government was "open-minded" about how to tackle the problem and an expert panel was reviewing the situation.
The number of deaths associated with novel psychoactive substances - otherwise known as legal highs - rose from 10 in 2009 to 68 in 2012, according to data published in the National Programme on Substance Abuse Deaths (NPSAD) report, compiled by experts at St George's, University of London.
The full list of festivals participating is: T in the Park, Bestival, Lovebox, Global Gathering, Secret Garden Party, Sonisphere, We Are FSTVL, 2000trees, ArcTanGent, Kendal Calling, Festibelly, Blissfields, Truck, Brownstock, Y Not Festival, Tramlines, Belladrum Tartan Heart, Leefest, Nozstock, Wakestock, Shambala, Glasgow Summer Sessions, Parklife and Eden Sessions.