A police force on a pole

Broadway lit by Brush lamps in 1881, New York City

From The Age of Edison: Electric Light and the Invention of Modern America by Ernest Freeberg: 

When electric streetlights were first installed by American cities in the 1880s, they were hailed as the solution to crime, especially by the companies selling them:

"Many nineteenth-century commentators believed that their own age was characterized by a particular hunger for light. Perhaps that's because, in the densest parts of urban America, the world had grown darker. Coal consumption skyrocketed in the rapidly growing cities and industrial valleys, providing heat to residents and driving the steam engines of an increasingly mechanized economy. City air filled with soot and smoke and, on bad days, produced 'fogs' dense enough to turn midday into an eerie dusk. The electric light, first on streets and soon in homes and offices, seemed just the thing to pierce through this man-made murk, the only way to compensate for the loss of sunlight in the modern industrial city. No one noted the irony that coal-powered electricity produced both smoke and light, the poison and the antidote -- most likely because the only option less polluting than electric power would have been to live with less light?
"Gilded Age cities seemed not only darker but more dangerous, and lighting companies marketed their product as nothing less than a police force on a pole. After nightfall, urban parks became notorious danger zones, a haven for the city's dregs and an infernal playground of indecency. Now all that could end, not by converting sinners or reforming criminals, but by harnessing light's power of exposure. As the mayor of Baltimore put it: 'An electric light is a nocturnal joy to an honest man, but a scarecrow to a thief.' Friends of the Light in Los Angeles, California put the formula more dramatically. 'The brighter the light,' they reasoned, 'the better for truth, purity, and honor, and the worse for fraud and all that fearful spawn of evil which flourishes in the darkness.' Frustrated by the slow development of electric street lighting in England, British reformers applauded what they called this 'American theory' that 'each electric light is as good as a policeman'.
"Throughout the 1880s, as cities erected powerful arc lights in city parks and boulevards, they hoped to win control of these civic spaces for law-abiding citizens. Most working people toiled until well after dark, especially in the winter months, so strong lighting helped to make these places useful to more people more of the time. For example, those advocating for the 'respectable working girls' on New York City's East Side called on the city to install lights in the riverfront park to stop 'roughs' from using the cover of darkness to insult women. The chairman of the Republican state committee in Illinois even found the light useful in cleaning up Chicago's notoriously corrupt elections. He spent thousands of dollars on election night in 1886, rigging powerful locomotive headlights at the polling stations to expose the Democratic 'ballot-box stuffers, shoulder hitters, and ruffians' who usually controlled the polls after dark. As soon as the lights came on, he reported with great satisfaction, 'the scoundrels could be seen slinking away into the alleys and shadowy places'.
"Temperance and vice reformers also embraced 'the modern light' as a tool for exposing their neighbors' 'deeds of darkness'. Under the cover of night, otherwise respectable men felt no shame when they tumbled through the streets at all hours, and had to be 'taken home by the police'. When lechers, thieves, and drunks were forced to do their evil deeds under strong streetlights, the eyes of every person in town were drafted to serve in a voluntary police force. Storeowners adopted similar strategies to protect their premises at night.
"New York City electricians argued that the cities police records confirmed this argument, as arrests for robberies declined steadily each year in the decade after electric lights were installed. Such claims are suspect, of course, as the stronger light more likely had the same effect on criminals that it does on cockroaches, not eliminating them but simply pushing them into darker corners of the city."

Rico says that lechers operate in dimly-lit bars now...