1. Road Lights and Neighborhood Lights Have Different Owners and Purposes
On a night walk, you might see lights on large roads where buses run, and thinner lights on utility poles in quiet neighborhoods. Both are often called "street lights," but they may have different owners and goals. The Ministry of Land, Infrastructure, Transport and Tourism sets standards for road lighting facilities on roads managed under the Road Act. These lights are designed to support the safety of cars and people using the road at night [1].
In contrast, "security lights" in narrow residential streets have different owners. In Utsunomiya City, standards define security lights as lamps installed, owned, and managed by organizations to ensure pedestrian safety and prevent crime. These organizations are local resident groups, such as neighborhood associations. The basic rule is to install them at least 4.5 meters (about 15 feet) above the ground, usually on utility poles [2]. This is just one example from Utsunomiya; rules vary by municipality. So, how bright should a light for walkers be?
Road lighting is positioned as a facility to support traffic safety at night. In Utsunomiya, security lights are defined as lamps managed by local groups to ensure pedestrian safety and prevent crime.
2. Why Street Lights Are Spaced by How Far Ahead You Can See
The distance between street lights is not decided by feeling, but by a guideline: "How far ahead can we see clearly?" For security lights, the Japan Security Systems Association has an industry standard (SES E1901-4). Class A brightness lets you see the general outline of a person's face 4 meters (about 13 feet) away. Class B brightness lets you see a person's behavior and posture at that distance. The association explains that this is the brightness where someone planning a crime might hesitate because they feel the danger of being seen. This is the association's explanation, not a proven fact that crime always stops [3].
Utsunomiya City's standards set the spacing for security lights to generally ensure Class B brightness. This means they set the interval to roughly maintain Class B levels, though there are exceptions depending on the road shape. This association standard is for security lights, not main road lighting. To feel this distance, 4 meters is about 5 to 6 steps for an adult, depending on stride length. The distance where you can recognize faces or movement is shorter than many people think.
The association explains that this brightness makes potential criminals hesitate due to the risk of being seen. To grasp the numbers, 4 meters equals about 5 to 6 adult steps, varying by stride.
3. How LED Street Lights Changed Where Light Falls on the Road
Street light technology has changed over time. Japan's first gas lamp was lit in Yokohama's Bashamichi in 1872. It burned gas made from coal, using the flame directly for light [5]. Gas lamps appeared on Ginza Street in Tokyo in 1874, and the first electric street light (arc light) in Japan was installed in Ginza 2-chome in 1882 [6].
Later, when LEDs began to be used for security lights, new problems appeared. LEDs have strong directionality, meaning they send light in a specific beam. Even if they met Class A or B brightness standards, light sometimes did not reach the edges of the road. If the edge of the path where people walk is dark, it fails the purpose of the standard [3]. To fix this, a standard for checking brightness at the road edge (Class B+) was added and included in the main text of the standards by 2015. As light types change, we must check if light reaches the places where it is needed.
Because LEDs have strong light directionality, light may not reach necessary spots, lowering the safety and comfort level of walking spaces.
4. Did Adding Street Lights Make Towns Safer at Night?
Is there a link between street lights and night crime? In New York City, USA, an experiment placed about 400 temporary lighting towers in randomly selected public housing projects. The study period was from March to August 2016. Reports suggest that in the housing projects with more lighting, serious crimes occurring outdoors at night decreased by at least 36%. A 36% drop means that if there were 100 crimes, there would be about 64 [4].
However, this report is a working paper, meaning it has not yet been peer-reviewed by experts. The results are limited to outdoor night crimes in public housing. We cannot say that street lights in Japan would have the exact same effect. Still, it shows that research exists which tries to test the relationship between light and night safety using experiments. If light makes the night safe, is brighter always better?
5. How Outdoor Lights Can Harm Rice Plants and Insects
The Ministry of the Environment's "Light Pollution Countermeasure Guidelines" includes road lights, security lights, and street lamps. It states that outdoor lighting should get the necessary brightness with as little power as possible, and that artificial light should not cause bad effects [7].
One example of a bad effect is on rice. Rice plants produce ears (heading) when days get shorter. Night lighting can delay this timing. The effect is strongest 20 to 40 days before the ears appear. For the Koshihikari rice variety, delays were noticeable with night lighting of 5 lux or more. In studies using LEDs, a 5 lux light delayed heading by about 13 days. Delays that do not affect yield are said to be within 3 days. Results change based on the rice variety and light color, so these numbers are just one example [7].
Insects are also affected. A study in the Thames River basin in the UK looked at 55 sites. Newcastle University announced that under LED street lights, hedge moth larvae were 52% fewer than in places without lights. Under sodium lights, they were 41% fewer. In grasslands, LEDs reduced numbers by about one-third, while sodium lights had a smaller effect [8]. A 52% reduction is almost half. From this, we see that light design needs to consider not just human safety, but also the living things around us.
6. How LED Lights Can Be Aimed Only Where They Are Needed
The "strong direction" of LEDs mentioned earlier is a drawback, but also a benefit. Because the direction is easy to control, we can aim light where it is needed and reduce it where it is not. In the 2021 revision of the Ministry of the Environment's guidelines, LEDs are described as easy to control for light distribution. The guidelines suggest reducing upward light as much as possible, because upward light does not help daily life and affects the night sky, birds, and insects [9].
The role of a street light is not just "to make the road bright," but "to let people see each other." If that is the goal, adding light where it is missing and reducing it where it is excessive does not contradict the light's purpose.
The purpose of street lights is to let people walk safely at night.
7. An Activity: Count Your Steps Between Two Street Lights
You can do this today. At night, walk near your home with an adult. When you find one street light, count the steps to the next one. Remember, 4 meters is roughly 5 to 6 adult steps, depending on stride length. More steps mean a wider gap between lights. Check if you can see the face and movement of a family member standing 4 meters away under the light. This helps you understand the thinking behind the standards. Always walk with an adult at night and watch for cars.
If you want to read more, search for "Security Light Installation Standards" with your town's name. You might find local rules. Look for details like who installs them and their height, similar to the Utsunomiya City standards [2].
Walk with a guardian at night and count steps from one light to the next. 4 meters is roughly 5 to 6 adult steps, depending on stride length. Always walk with an adult at night and be careful of cars.