Respecting the rest and wildlife

The new lights that has been installed in our city are formed by LED technology but… Who is this technology and what benefits does it bring to our health?

Any light source, whether natural or artificial, can affect our health in different ways, either ¹⁾by its intensity (increasing eye temperature or dazzling), ²⁾by flickering (also called strobe effect) or ^{3 )}for the light spectrum it has. In the following lines, we will break down these factors and link them with LED technology.

The first of the factors that we will talk is about the Intensity. It is necessary to differentiate what is the lighting LED and what is laser LED. The kind of luminary that has been installed in our city are lighting LEDs and, therefore, they do not produce any type of heating in the eyes, unlike the one laser LEDs produce and that can be dangerous. Glare can occur when the light intensity is high and reaches our eyes directly. The type of our city luminaire has a vertical position and the light is focused towards the ground: therefore, if we do not look directly at the light source there is little danger of being dazzled.

Flickering light or strobe effect is present, although not noticeable, in almost all artificial light sources. The LEDs that have been installed have a blinking frequency greater than 200Hz and, therefore, the physiological impact that our body may have (headache, discomfort, vision disturbances...) is drastically reduced.

We will make special mention of how the Light spectrum can affect us. The biorhythm of most animals is related to exposure to sunlight (day / night) and we are no exception. The spectrum of light that the Sun emits varies throughout the day and we notice it effects on our activity: we generally have more energy in the morning and, as the night approaches, our energy decreases. The brain associates greater physiological activity when there is light, and at night it inhibits this function, reaching a minimum between 3:00 and 6:00. However, how does our body detect the light?

Although we are asleep, the light is captured by cells that are located below the retina and direct the information to the nucleus of the Central Nervous System (also called the suprachiasmatic nucleus), which regulates the internal sleep / awakening clock. This gives the body the order to start secreting certain substances that control the body's rhythms: for example, when it is dark, it gives the brain the order to secrete melatonin, a hormone that our body generates and that affects sleep. These cells are very sensitive to the blue wavelength, naturally present in the blue sky, but also on LCD screens, smartphones, computers, tablets, LED lights and some lightbulbs. Due to this effect, a brief exposure to this type of light at night can deceive our body and make the body behave as if it were daytime. However, how can we know if the light used by the devices are blue? This can be known by the colour temperature.

When we go to the store and we are in front of the endless shelves with different types of LED bulbs, we can see that there isn't some specification from the manufacturers about what method they use to generate the light. It can usually be origined by four forms: ¹⁾three LEDs of different colors (generally red, blue and green), ²⁾by a blue LED and a yellow phosphor giving a warm white color, ³⁾by a blue LED and another phosphor (giving a white color cold) or ⁴⁾by means of an ultraviolet LED and three matches. This would be interesting to know since methods 2 and 3 are cheaper, but generate an important blue component. While methods 1 and 4 are relatively more expensive than the previous ones, but they generate little blue component since it is controlled independently. These this would be the option that we would be interested in choosing since it affects our biorhythm less.

Instead, we observe that lightbulbs are classified according to Color temperature. What is it and what information does it provide us? Color temperature is a numerical measure in Kelvin degrees n (ºK) that serves to describe the tonality of light from a specific light source and allows a comparison to be made between different types of LEDs on the market. There are three types of light shades depending on the color temperature (Fig. 1):

• Warm (color temperature between 2.800 and 3.500ºK). Color shades are close to the red wavelength (the light is similar to light provided by incandescent bulbs) and provide ambient warmth.
• Neutral (color temperature between 3.800 and 4.500ºK). It’s considered a more natural light and is used to beautify colors and produce a natural effect.
• Cold (color temperature above 5.000ºK). Equivalent to daylight with a lot of sun or a cloudy day. Therefore, the wavelength it emits is close to blue and provide a stimulating environment for the animal's biorhythm.

Figure 1. Classification of the type of light emitted by LEDs based on color temperature. A comparison can also be made with the different types of light that we know and are usually in contact with. Source: Image modified from B · LED Barcelona Led.

Once we have introduced the concept of color temperature, we can ask ourselves what do we have in our city? The luminary that has been installed within the city has a neutral hue since the color temperature of the LED bulbs is 3.000ºK; while the luminaire of urbanizations that are in wooded areas such as Can Palet de Vista Alegre and Les Martines, among others, can have a warm hue with a color temperature between 1.200 and 2,400ºK. Why this difference in temperature of lightbulbs between the city and housing estates? If we look at the Terrassa map, these areas are in direct contact with "l'Anella Verda" (Fig. 2) which is the territory of natural and rural environment, with forests, fields and streams that surround the city of Terrassa .

Figure 2. Territory that groups the Anella verda de Terrassa. Source: Image extracted from the Guide to the Anella Verda of Terrassa that can be downloaded on the web of Anella Verda.

At the beginning of this article we have commented that the biorhythms of all animals, including us, are related to the sunlight. By illuminating those urban areas that are in contact with forested areas with warm lightbulbs, we reduce the disorders that we can cause to wildlife, such as prey-predator relationships, migrations, disturbances of circadian rhythms (linked to light exposure and, therefore, to the alternation between day and night) of fauna, biological cycles (reproduction)…

We must be aware that we must manage correctly and efficiently the type of LED lights that we use to minimize the impact that we can cause, with our actions and decisions, to the other living beings that live with us on this planet.