Light and Human Vision

• Light in physics refers to electromagnetic radiation of any wavelength, visible or not.
• Visible light is electromagnetic radiation within the electromagnetic spectrum portion perceived by the human eye.
• Different species have different visual sensitivities.

Human Vision

• The most important mechanism for apprehending the world.
• Results from the interaction between the eye and brain.
• Light enters the eye through the pupil, a circular opening.
• Light then reaches the lens, which focuses the image by changing its shape.
• Light is absorbed and converted into signals at the retina.
• A layer of photoreceptors on the retina encodes the image as neural signals.
• These signals are conducted to the brain's center through neural pathways.
• There are four photoreceptor types; Rods, L-cones, M-cones, and S-cones, that are distributed in different areas across the retina and have different spectral sensitivities.

Photoreceptive Cells Composition

• Rods:
  • There are 120 million.
  • Concentrated in the outer edges of the retina.
  • Require less light to function.
  • Responsible for night vision.
• S-cones:
  • Absorb blue.
• M-cones:
  • There are 8 million.
  • Concentrated in one small area that lies on the visual axis of the eye (fovea).
  • Function under bright light.
  • Absorb green.
• L-cones:
  • Absorb red.
• Cones are responsible for color vision.

Spectrum of Natural Daylight

• Natural daylight contains a rainbow of colors from around 380 nm to 780 nm.
• The spectral power distribution curve can represent the radiation power output at each wavelength.

Spectrum of Artificial Light Sources

• The spectral power distribution of artificial light depends on its working principle.

Evolution of Life Style

• In the past 150 years, human activities have undergone radical transformation.
• People moved to cities from the country.
• Life style changed from mainly outdoor to mainly indoor.
• Visual environment changed from natural daylight to artificial light.
• 150 years is a short period compared to human evolution.
• Exposure to artificial light is a recent introduction.

Circadian Rhythm

• The raising and lowering of leaves in plants repeats during days and nights in the 18th century
• Continues even when the plants are placed in the dark, indicating there is an internal biological clock mechanism in the plant.
• Humans and all living things exhibit changes in behavior that occur over a 24-hour cycle which a natural, internal process that regulates the biological clock.
• Circadian rhythms are self-sustained and adjusted to the local environment by external cues, most importantly daylight.
• The circadian clock runs for slightly longer than 24 hours for most individuals without any light, causing waking and sleeping to occur incrementally later each day.
• Light impacts powerful biological effects that regulate human health, performance, and well-being.
• Melatonin, a key hormone linked to the 24-hour light-dark cycle, regulates sleep-wake patterns and is produced when it is dark.
  • Daytime exposure to light helps us stay awake.
  • Darkness helps us fall asleep.
• Sleep deprivation is related to cognitive performance, physical and mental fatigue, mood changes, and health risks like obesity and diabetes.
• The amount of artificial or natural light in interior spaces is lower than that found outside causing the amount and the timing of the light may not be able to correctly stimulate our circadian system.
• Natural light is the best light source to synchronize and regulate biological clocks.
• Sunlight and skylight have two fundamental characteristics: both the timing and quantity suitable for a correct phasing of the human circadian system.

Daylighting

• Daylighting provides the opportunity for both energy savings and improved visual comfort.
• With proper integration of a well-designed artificial lighting system, it can offer significant energy savings by reducing a portion of the electrical lighting load.
• It can also lower cooling load due to the reduction in heat gain from electric lamps.
• It helps create visually pleasing and productive environments for building occupants.
• Simple daylighting systems consist of an aperture to let daylight reach building interiors.
• The aperture can be on the top of the building (toplighting, roof lights) or the side of the building (side lighting, windows).
• The aperture is usually glazed but can also be unglazed.
• A light shelf is a horizontal surface that reflects daylight deep into a building.
• Light shelves are placed above eye-level and have high-reflectance upper surfaces that reflect daylight onto the ceiling and deeper in the space.
• Light pipe systems have a daylight collector, a transmitter and an emitter.
• The collector gathers daylight on the exterior of the building.
• The transmitter transmits daylight into building interiors.
• The emitter distributes the daylight to the interior space.

Solar Shading

• Sunlight admitted into a building impacts on the building energy consumption in different ways in different seasons.
  • In summer, excessive solar heat gain results in greater energy consumption due to increased cooling.
  • In winter, sunlight reaching the south-facing facade can provide passive solar heating.
  • In all seasons of the year, the sun improves daylight quality.
• Well-designed shading devices significantly reduce building peak cooling load and corresponding energy consumption and enhance daylight utilization in buildings.
• Shading devices can also avoid glare by reducing contrast ratios of the building interior.
• Shading can also be provided by natural landscaping or building elements.

Daylighting Shading examples:

• Overhang Horizontal panel, which works best facing South, East and West, can trap hot air.
• Vertical fins can be loaded by wind and snow which restrict the view for north facing facades in hot climates only.
• Slanted horizontal louvers that slant towards the north, reduces wind but also restricts the view.
• Eggcrate, which traps hot air views are restricted for very hot climates.
• Slanted fins facing East and Wes which slant towards the north but also restricts the view and also traps hot air for very hot climates

High-Performance Glazing

• Glazing is an important element in buildings and offers daylighting and ventilation for a building's interior.
• Studies show that health, comfort, and productivity of building occupants are improved due to well-ventilated indoor environments and access to natural light.
• Windows represent a major source of heat gain/loss, visual and thermal discomfort.
• High-performance windows feature multiple glazing, specialized transparent coatings, insulating gas in between glass panes, and improved frames which reduces heat transfer and able to cut energy burden due to the window openings.
• In air-conditioned buildings, the temperature difference between indoor and outdoor environments could be large in summer and can be minimized with glazing to prevent electricity consumption.
• An appropriate choice of windows with low thermal transmittance characteristics (multiple glazing, specialized transparent coatings, insulating gas in between glass panes) can minimize solar heat transmission.
• Reflective glass usually consists of a thin metallic coating that helps control solar heat gain but typically blocks more light than heat.
• Insulated glazing typically refers to double or triple glazing, where two or more panes are spaced a distance apart and hermetically sealed, creating an insulating air space in-between each pane.
• In gas-filled double or triple glazed windows, instead of air, the space is filled with argon or krypton gas, which provides a superior resistance to heat flow.
• Spectrally selective glazing permits some solar spectrum portions to enter a building while blocking others, screening out or reflecting heat-generating UV and IR radiation while permitting the most visible light.
• Electrochromic glazing is glass or glazing whose light transmission properties are altered when voltage, light or heat is applied, changing from translucent to transparent.

Light Pollution

• Light pollution in Hong Kong is the 'worst on the planet'
• Light pollution is defined by the International Dark-Sky Association (IDA) is any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste which disrupts ecosystems and may have adverse health effects.
• According to CIE International Lighting Vocabulary (CIE S017, 2011), light pollution is defined as the sum total of all the negative consequences due to artificial lights, while obtrusive light occurs when light spills annoyingly and reduces visibility to essential information.
• Light pollution is a side effect of industrial civilization that includes building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues.
• Light pollution can cause adverse effects on environmental due to excessive outdoor lightings.
• Birds are often waylaid by buildings in urban areas and often die in collisions with windows.
• Artificial light can cause birds to wander off course and toward dangerous nighttime landscapes, while it can affect insect mortality and egg laying turtle behavior.
• Plants depend on the natural cycle of day and night. Artificial light at night also throws off a plant's response to the change of seasons.

Possible effects of obtrusive light

• Obtrusive light gives rise to annoyance, discomfort, distraction, or a reduction in ability to see essential information and may lead to light trespass, over illumination, and glare from over-lit facades.
• Light trespass occurs when unwanted light enters one's property.
• A common light trespass problem occurs when a strong light enters the window of one's home from the outside, causing sleep deprivation.
• Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity.
• Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light.
• Sky glow and light clutter are other consequences.
• Wasteful energy consumption, air pollution, and global warming are also side effects.
• The International Commission of Illumination (CIE) has outlined four environmental zones.

The International Commission of Illumination environmental zones for controlling regulations:

• Intrinsically dark in National parks or protected sites.
• Low district brightness in Industrial or residential rural areas.
• Medium district brightness in Industrial or residential suburbs.
• High district brightness in Town centers and commercial areas.
• Recommendations by CIE include upward light ratio (ULR), limitation of sky glow, illuminance on vertical plane, limitation of illumination on surrounding properties, limitation of bright luminaires in the field of view.