Many women shoot selfies for posting on social networking websites at a pool open after sunset. (Video by Takeho Morita)

On a recent summer's evening, Tokyo Prince Hotel opened its pool for new after-sunset hours.

Soon, many women in swimsuits were floating on shell- or flamingo-shaped toys and taking selfies with the iconic Tokyo Tower in the background. However, no one was swimming.

“I can't swim, but I came here to snap photos,” said a 25-year-old female company employee on July 8. “Such images, if posted on social networking websites, will generate a huge response.”

A rapidly increasing number of luxury hotels and theme parks such as the Tokyo Prince Hotel are opening their swimming pools after sunset, which are proving popular with young women who want to post photos that look as if they were taken at a resort.

The move comes as operators of hotels and amusement parks are struggling to attract a wider range of customers.

At Tokyo Prince Hotel in the Japanese capital's Minato Ward, the hotel operator, working with a female fashion magazine publisher, set up lighting along the poolside to provide a picturesque setting for visitors. With the water and poolside illuminated in assorted colors in the background, many young women were shooting photographs with their smartphones and selfie sticks.

The hotel operator opened a swimming pool after sunset at another facility last summer. The evening pool service proved so popular that it decided to offer a similar service at Tokyo Prince Hotel this summer. The admission fee is 4,200 yen ($37) for women and 6,000 yen for men.

Hotel New Otani started offering evening pool hours on July 15 in Osaka, July 21 in Tokyo and July 26 in the Makuhari district in Chiba Prefecture.

The hotel operator started offering evening pool hours in Tokyo in 2001. After the service generated a positive response, Hotel New Otani began providing the same service at multiple facilities three years ago.

While cocktails will be available at poolside, which is lined with palm trees, events are also planned in which a disc jockey will play dance music.

Many facilities started operating evening pools, after Japanese companies introduced changes to work hours as part of their efforts to save power amid electricity shortages following the 2011 Great East Japan Earthquake and tsunami.

Targeting male and female company employees who left their offices earlier than usual, hotel operators in Tokyo publicized their evening pool services, attracting many young women who wanted to stay out of the sun but wanted to enjoy bathing in swimwear.

As guests of upscale hotels are mainly middle-aged and elderly people, hotel operators started more aggressive efforts to promote their evening pools to attract younger customers.

Japanese businesses are improving their work environment by reducing overtime hours. Serving and consuming alcoholic beverages, as well as playing music with audio equipment, have been banned on beaches across the country.

Those factors have also apparently helped the spread of evening pool services.

Most customers of leisure facilities are families and fewer young people visit those facilities. After evening pools at hotels created a buzz, leisure facility operators began following suit.

Huis Ten Bosch, a theme park in Sasebo, Nagasaki Prefecture, started an evening pool service on July 1, while the swimming pool was also open after sunset last summer.

Laguna Ten Bosch, a resort facility in Gamagori, Aichi Prefecture, and Ren, a spa ryokan in Kobe, opened their pools in the evening for the first time this year.

Toshimaen, an amusement park in Tokyo’s Nerima Ward, is expected to reopen its pool in the evening on July 28 for the first time in 30 years.

Yohei Harada, an official of the Hakuhodo Brand Design Youth Life Lab, said the offering will become much more popular in the future.

“Young people’s capabilities of spreading information through social networking services is so high that companies cannot ignore their presence,” said Harada. “They helped the popularity of Halloween-related events grow so drastically.”