Why are streetlights being replaced with LED light
For those born before the 2000s, streetlights have always been a warm amber colour due to sodium-vapour lamps. These lights come in two main varieties, low pressure and high pressure. Such lamps utilize a low-pressure gas (argon, neon, or a mixture), along with a small piece of solid sodium that is melted and vaporized when turned on. Once vaporized, very little energy is needed to excite the sodium (making sodium lights very energy efficient) and emit a very narrow frequency range of light (similar to a laser).
While these lights have been ideal for the past 70 years thanks to their efficiency (compared to other old lamp technologies), they are being replaced with LED variants. These lights are being replaced for the sake of efficiency. Modern low-pressure sodium lamps are only less efficient than LEDs.
One reason for replacing streetlights with LEDs is that older streetlights only produce yellow light, hindering visibility for pedestrians and drivers. Research has shown that LED lights (which produce white light) can improve peripheral vision at night, reduce braking distance, and help drivers see obstacles better.
Another reason for replacing street lights with LEDs is that LEDs offer directionality which helps to keep light away from the upper atmosphere. This can be highly advantageous for astronomers using high-end telescopic equipment who need to have clear skies with minimal light pollution.
There are many models now available for energy saving in compact sizes.