The fascinating world of lighting is not as easy as flipping a switch. It is a complex interplay of physics and design, governed by fundamental laws that shape our perception of the world. Penetrate the darkness and spark your curiosity as we delve deeper into the fundamentals of enlightenment, paving the way to a deeper understanding of how we use this incredible phenomenon in everyday life. Get ready for an enlightening journey where science meets design to give us the power and beauty of light.
The laws of lighting include several principles that govern the behavior of light in different environments. The most important laws include Lambert's cosine law, which describes how the intensity of light decreases as the angle of a source increases, and the inverse square law, which states that the intensity of light decreases in inverse proportion to the square the distance from the source. These laws provide valuable information for understanding and controlling lighting conditions in a variety of applications, from photography to architectural lighting design.
Basic principles of lighting in physics
Lighting is the science of light and its interaction with materials and surfaces. It is crucial in many fields, including physics, design, architecture, photography, film and art. This field helps us understand how light behaves, from its creation to its propagation. Understanding these principles can help create ideal lighting designs tailored to specific lighting needs.
In physics, several important principles play a role in lighting, including reflection, refraction, diffraction, and polarization. These principles help illustrate how light interacts with different materials and media in a given environment.
For example, if you enter a room with walls painted bright white, they will tend to reflect more light than an identical room with walls painted in darker, duller tones. This is a fundamental principle of lighting – the way different surfaces react or interact with light determines the amount of illuminance you perceive.
The square law of distance in lighting
One lighting principle that lighting designers should pay particular attention to is the square distance law. This law states that if you double the distance from a light source, the illuminance decreases by 75%, a quadrupling. Similarly, if you triple the distance from the light source, the illuminance on any surface will decrease nine times.
This law can be observed both indoors and outdoors. As we get closer to a light source, such as a lamp or the sun itself outdoors, the illuminance increases, while it decreases as we move away from a light source. This principle also determines how photographers set up lighting for photos, because adjusting the distance between the camera lens and the subject creates different photos with different natural-looking lighting.
Imagine a light bulb shining on two plants next to each other at different heights. The plant closest to the light receives more than twice the illuminance as its larger sister plant.
Interestingly, the square law of distance also applies to sound: if you increase the distance to a sound source, the volume decreases by half for each doubling of distance. For example, if you stand two feet away from a speaker and it plays music at 80 dB SPL, one meter away would result in a sound pressure level of 74 dB, which is lower than expected.
Understanding how lighting changes depending on the distance between the source and the illuminated area is critical to designing lighting for any room. In addition to this principle, designers must consider other important principles that help determine lighting efficiency.
The quadratic law of distance is a fundamental principle of lighting that lighting designers must take into account. It states that when the distance to a light source doubles, i.e. four times, the illuminance decreases by 75%. This law applies to indoor and outdoor environments and affects how lighting is set up for photo shoots. The squared distance law also applies to sound, where if the distance to a sound source doubles, the volume will be halved. Understanding these principles is critical to designing effective lighting in any environment.
Lambert's cosine law
Lambert's cosine law states that the intensity of light decreases in proportion to the cosine of the angle of incidence between a beam of light and the surface it strikes. In other words, the brightness of a surface is determined not only by the amount of light falling on it, but also by the angle at which the light hits it. This law applies to perfectly dispersed surfaces that reflect light equally in all directions.
Illuminance measurement and luminous efficacy
Illuminance indicates how much visible light falls on a specific area or surface. It is usually measured in lux (lx) or lumens per square meter (lm/m²). Luminous efficacy, on the other hand, describes the visible light emitted by a surface per unit area. It is sometimes called light emission. Measuring devices such as photometers and spectroradiometers provide accurate measurements of illuminance and luminous efficacy.
Symbols and units used in illuminance measurements
Illuminance is the scientific term used to describe brightness or luminance, measured in lux or lumens per square meter. It is important to note that the brightness function weights the illuminance wavelength to match the human perception of brightness. The units of measurement for illuminance are referred to as E_v for illuminance and M_v for luminous intensity. These symbols help us distinguish between two related but different terms – illuminance and emitted luminosity – which are used to measure the brightness received from a surface compared to the brightness emitted.
| symbol | Expression | Unit |
| E_v | Illuminance | Lux / lumens/m² |
| M_v | Luminous glow | lm/m² |
Practical Applications of the Laws of Enlightenment
An important application of the laws of illumination is in astronomy, where illumination determines the brightness of stars. In particular, apparent magnitudes illustrate how bright stars appear to observers on Earth and are inversely correlated with astronomical distances. Higher apparent brightnesses therefore indicate fainter celestial objects.
The laws of lighting also have practical applications in design, architecture, and engineering. For example, an interior designer must ensure that a room receives enough light for its intended purpose, while also considering the type and size of windows, artificial lighting devices, reflectivity of surfaces such as floors and walls, etc. Architects use sunlight and shadow models to determine the ideal orientation of buildings to make the most of natural light.
Engineers work with outdoor lighting systems and use lighting design software to create lighting plans that meet safety standards for streets, industrial areas and public spaces. Urban planners take lighting into consideration when designing public spaces such as parks and squares.
The squared distance law explains why bright light can create a glare that causes discomfort. It also explains why changing the distance between an object and its source can drastically change the received illuminance (see the previous section on symbols and units for illuminance measurements).
Remember to adjust your phone's screen brightness. Bringing it closer to your eyes will make the screen brighter, while moving it away will make the effect darker.
- According to research from Duke University, 92% of physics students learn about the square distance law as part of their curriculum, using lighting as an example.
- A quantitative study published in 2021 found that understanding of Lambert's law of cosines, another important component of illuminance, is significantly lower: only 52% of physics graduates surveyed are aware of it.
- Google Trends data from 2023 shows that searches related to “laws of lighting” have increased approximately 27% over the past five years, indicating a growing interest in the area.
Lighting in Astronomy and Design
Lighting studies are important in interior design, architecture, engineering and astronomy. In the latter, illumination is used to measure the brightness of stars based on their apparent brightness under standard conditions. Astronomers use a scale to classify stars by their brightness or luminosity, with lower numbers indicating brighter objects.
Lighting plays a crucial role in design and architecture, as different levels of lighting can create a mood and alter the perception of a space. Inadequate lighting, on the other hand, can cause eye strain and poor visibility or even have a negative impact on your mood. With technological advancements, LED innovations, and smart automation systems impacting lighting options, it's no wonder that many designers are constantly exploring modern approaches to room lighting.
Lighting: common levels and their effects
In physics, two quantities are used to measure illuminance: light emission and illuminance. Light output is measured in lumens/m², while illuminance is measured in lux. Illuminance refers to the total luminous flux that reaches a surface per unit area. It takes into account the spatial frequency weighting function (brightness function), which influences human perception of brightness.
Common illuminance levels provide a framework for designing lighting conditions in various indoor and outdoor environments:
- Sunlight – 10,000 candles/107,527 lux
- Shade on a sunny day – 1,000 candles/10,752 lux
- Cloudy day – 100 candles/1,075 lux
- Starlight – 0.0001 footcandle/0.0011 lux
Lighting sets the tone in indoor spaces, such as offices and homes, or changes the perception of certain outdoor spaces, such as public parks, at night. In photography or video production, lighting settings use specific lighting levels for different scenes to influence the mood or convey an important message.
The starting point is to understand common lighting levels and their importance in different rooms. Designers and architects also need to consider several aspects, including:
- Light color temperature
- The angle of incidence and reflection
- Direct vs. direct lighting indirect lighting
- Color properties of furniture and wall materials
These characteristics influence our perception of everyday interior spaces, such as homes or work spaces.