A regulation proposed by the EU would set the theatre industry “back by decades”, according to producer and West End theatre owner, Nica Burns.
Energy efficiency rules currently under consultation would ban “the manufacture and sale of everything we use”, Matt Drury, head of lighting at the National Theatre, told BBC News.
It would “undoubtedly” force some theatres to close, he said.
The EU say no decision has been taken and none is due before the end of 2018.
Under the Eco-design Working Plan 2016-2019 the European Commission wants to bring most theatre lights under the same rules that govern domestic, office and industrial lighting.
The proposals aim to improve the environmental performance of products including vacuum cleaners, tumble driers, heaters and lights.
Legislation introduced in 2009 banned retailers from selling tungsten lighting for domestic use, but permitted them to do so for use in theatres.
If given the go-ahead, the European Commission proposals would abolish the exemption allowing theatres to use tungsten bulbs.
The Association of Lighting Designers say that the proposals will bring “theatre lights under the same rules that govern domestic and office and industrial lighting”.
“It’s trying to make [lights] as bright as possible using the least amount of energy”, said Mr Drury.
However, he believes this is unrealistic given current technical limitations.
“By 2020 the world of science will not have allowed technology to have evolved to that point,” he added.
Ms Burns, who received an OBE in 2013 for services to theatre, agreed.
She said the proposals, if confirmed, would be a “disaster” due to the huge financial costs involved.
“Every tiny youth group that has a stage where they do their plays, every school theatre and any sort of community hall, are going to have to spend a lot of money which they simply don’t have,” she said.
There are also concerns its impact could stretch beyond West End and local stages.
Tim Routledge, responsible for designing the lighting used by Beyonce and Sam Smith’s during their most recent stadium tours, said the impact of the proposals could be seismic for the industry – affecting its biggest stars.
“If Taylor Swift of Lady Gaga were coming [to the UK], their equipment would not be viable.
“You would see very stark stages. Basically the cleaner’s lights they clean the arenas with,” he said.
According to Routledge, Brexit will not soften the blow, as he believes the UK will “adopt all the EU regulations so we can keep on trading [with them]”.
“Even if that weren’t the case, most of the manufacturers [of theatrical lighting] are based in Europe.”
In response. the EU Commission said they “welcome the input from theatres to the current consultation about future policy,” adding: “Member states are expected to vote on the decision around the turn of the year.”