Glossary

The ANSES report (2019) was produced by the French institute for health – the equivalent of the Health Protection Agency in England. It concluded that “The new scientific data confirm the 2010 result regarding the toxicity of blue light to the eye, which can lead to failing eyesight. They show short-term phototoxic effects associated with acute exposure and long-term effects associated with chronic exposure, which increase the risk of developing age-related macular degeneration (ARMD). “Warm white” domestic LED lighting is no different from traditional lighting and has a low risk of phototoxicity. In addition, the expert appraisal showed that even very low levels of exposure to blue light in the evening or at night disrupt biological rhythms and therefore sleep.”

Colour temperature is a measurement that describes the appearance of light emitted by a light source, typically measured in Kelvin (K). It is used to characterize the colour of light, ranging from warm to cool. A lower colour temperature, around 2,700-3,000K, is considered warm, resembling the light emitted by incandescent bulbs. As the colour temperature increases, the light appears cooler, ranging from neutral white (around 4,000K) to daylight (around 6,000K).

Our spectacular universe of planets, stars, galaxies and the Milky Way has been visible in the night sky for most of human history. But light pollution has obliterated the stars across much of the UK, with only a few of the brightest stars now visible and many people living in urban areas have never seen the Milky Way.

The International Dark-Sky Association advocates that any required lighting be used wisely. To minimize the harmful effects of light pollution, lighting should:

• only be on when needed
• only light the area that needs it
• be no brighter than necessary
• minimize blue light emissions
• be fully shielded (pointing downward).

The UK’s All Party Parliamentary Group on Dark Skies produced a policy document in 2020, listing actions needed to “reverse the exponential growth of environmental pollution caused by artificial light

Flicker (also known as temporal light modulation)  can cause migraines and also presents a safety hazard The light LEDs produce depends on the circuitry within the lamp, which changes alternating current to provide the low voltage the LED needs. Some circuitry is insufficient to reduce the variation in the supply voltage and this generates flicker. There is variation among LEDs in the degree of flicker, some do not flicker at all while others flicker badly. A particular problem occurs when people use unsuitable LEDs with domestic dimmer switches, which results in significant flicker and severe headaches. 

There is no reason why LEDs can’t be flicker free, except cost. The Swedish Government has calculated that the cost of eliminating flicker is equivalent to around 10 pence per LED. Flicker can cause health problems, even if it is so rapid that you can’t see it and are unaware of it. It causes headaches, eyestrain, migraines and disturb the control of eye movements. Flicker can disrupt the movement control of the eyes and force the brain to work harder, causing discomfort and migraine in some people. For people suffering from migraine, some LED bulbs are capable of inducing feelings of dizziness and pain within 20 minutes of switching them on. Checking flicker is relatively simple to do with a smartphone camera, and apps are available for smartphones that allow users to measure the degree and frequency of flicker. 

Fluorescent lighting is a type of lighting that uses a fluorescent tube to produce light.. Fluorescent lights operate by passing an electric current through a tube filled with mercury vapor, which emits ultraviolet light. This ultraviolet light then interacts with a phosphor coating inside the tube, producing visible light. However, it can sometimes be associated with flickering and a cooler color temperature, which may not be suitable for all environments or individuals with light sensitivities.

Compact fluorescent lighting (CFL) is a type of fluorescent lighting where the tube is bent or made into a spiral to fit in standard light fixtures, making them suitable for residential use.. CFLs have a longer lifespan than incandescent bulbs but take more time to reach full brightness when turned on. They also emit some UV light as the process of bending the tubes leaves small gaps in the phosphor coating.

The human eye can adapt to a wide range of light levels from bright sunlight to almost total darkness. However, comfortable vision requires a limited range of light levels at any particular time and excessive light levels and luminance contrasts can lead to glare. 

Glare can be experienced as disability glare or discomfort glare:

• Disability glare affects the ability to see and leads to some degree of temporary loss of vision and is produced by high luminance in a lower luminance scene, for example at night when a car with LED headlights comes over the brow of a hill or goes over a speed bump.  
• Discomfort glare causes irritation, anxiety, visual fatigue, and eyestrain and can adversely affect wellbeing. Depending on an individual’s sensitivity it can also cause dry or watery eyes, itchiness, tense muscles, breakdown of vision, blurred or double vision, headaches and fatigue.

An extreme example of glare are LED daylight-running lights on cars. These are clearly visible to other road users and pedestrians. At night, if they do not dim, they can be dazzling and more so for young children (who have higher transmission of light through to the retina) and for older people (who will suffer from scattering of the light, particularly in the lens of the eye). Older drivers, in particular, will be dazzled by oncoming vehicles with the risk that they may not see hazards until too late.

A health Impact Assessment (HIA) is a way to identify and improve the health consequences of any defined policy or proposed development, including unintended and unanticipated consequences. A HIA includes explicit consideration of how impacts may affect different groups in the population. HIAs produce evidence-based recommendations to inform decision-makers on how they can promote and protect the health and wellbeing of local communities they serve

Although Incandescent lighting, may be less energy-efficient than other lighting options, They offers a number of advantages over LEDs and CFLs.:

• Eye Health Incandescent lighting is gentler on the eyes, reducing the risk of eye strain and minimizing visual fatigue. Almost all light sensitive individuals are able to manage well with incandescent lighting.

• Sleep regulation: Exposure to bright, cool-toned light typical of LEDs in the evening can disrupt the body’s natural sleep-wake cycle. Incandescent lighting, with its warm color temperature, emits less blue light,making it easier to wind down for a restful night’s sleep.

• Warm ambiance: Incandescent bulbs emit a warm and inviting light, creating a cosy atmosphere in homes, restaurants, or other spaces where a soft glow is desired.

• Immediate brightness: Unlike some energy-efficient alternatives, incandescent bulbs instantly reach their full brightness when switched on, providing immediate illumination without any warm-up time.

• Versatility: Incandescent bulbs are/were  available in various shapes, sizes, and wattages, making them suitable for a wide range of lighting fixtures and applications.

• Color rendering: Incandescent bulbs have excellent color rendering capabilities, accurately representing colors in their true and natural hues.

• Dimming capability: Incandescent bulbs are easily dimmable, allowing users to adjust the light intensity to create the desired ambiance or conserve energy.
  
• Affordability: Incandescent bulbs are typically more affordable upfront compared to some energy-efficient alternatives, making them accessible for individuals on a budget.

A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Each LED emits light of only one particular colour. In street lights, this is usually blue, to make white street lights, a powerful blue LED is shone on to compounds called phosphors that absorb blue light and emit yellow light. This yellow light combines with the blue light and appears white to the eye. Most white-light sources emit a range of wavelengths, which, when combined, produce the colour of light perceived by the human eye. The resulting shade of white depends on the blend of phosphors and is measured on the colour-temperature scale. Colour temperature is conventionally expressed in Kelvins, using the symbol K, a unit of measure for absolute temperature. It is measured on a numbered scale, where the higher the number, the ‘cooler,’ or bluer the light, the lower the number, the ‘warmer,’ or yellower the light.

Early “white” LEDs were very blue and harsh on the eye. Adding more phosphors to a ‘white’ LED makes its light look warmer and less harsh, but at the expense of reduced efficiency, as energy is lost in converting high-energy blue photons to lower-energy photons. Unlike other forms of lighting which illuminate equally in all directions (isotropic), LEDs are highly directional with light emitted in an arc of around 60 degrees (anisotropic), rather than 360 degrees common in other lighting. LED light is usually emitted from a small, flat, surface, rather than a large, curved one. Because of this the vast majority of LED luminaire designs suffer from the acute drawbacks as they attempt to illuminate wide areas, some distance away from a small, flat light source. Also, LED light is not distributed evenly across its beam but concentrated on its axis. This causes problems of glare, for example, car headlights can be blinding to pedestrians and oncoming traffic when cars go over a speed bump or over the brow of a hill and shine directly in people’s eyes

The term “light disabled” is used in relation to describe individuals.who are particularly sensitive or adversely affected by certain types or intensities of light. These individuals may experience discomfort, pain, or other adverse reactions when exposed to bright or intense light sources. Their condition may be related to medical conditions such as photophobia or certain eye disorders.

Some people with pre-existing health issues find their conditions exacerbated by new forms of lighting such as LEDs. These include migraine and light-sensitive skin conditions. Others with no previous health issues also experience problems under new forms of lighting. Some experience severe symptoms, including searing eye pain, debilitating headaches, skin burning and rashes, dizziness, fainting and vomiting. For others, the symptoms are milder: anxiety, eczema, edginess or just a sensation of discomfort or ‘wrongness’ that is hard to locate.

Photophobia is a condition characterized by extreme sensitivity or intolerance to light. Individuals with photophobia experience discomfort, pain, or an intensified aversion to bright light sources, such as sunlight or artificial lighting. It can occur as a standalone condition or as a symptom of an underlying medical condition, such as migraines, eye disorders, or neurological disorders. Exposure to light can trigger symptoms like eye pain, headaches, nausea, and difficulty focusing. People with photophobia often find relief in darker environments or by wearing tinted glasses. Proper diagnosis and management of the underlying cause are essential for effectively managing photophobia.

The EU Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) published its opinion on Potential risks to human health of Light Emitting Diodes (LEDs) in June 2018. The report concluded that:

• There is no evidence of direct adverse health effects from LEDs in normal use (lighting and displays) by the general healthy population (i.e. the adult population excluding children, older people and people suffering from light sensitive conditions) 
• Some people report that they are sensitive to temporal light modulation from LEDs (i.e. flicker).
• Children have a higher sensitivity to blue light and although emissions may not be harmful, blue LEDs (between 400 nm and 500 nm) may be very dazzling and may induce photochemical retinopathy, which is a concern especially for children below three years of age.
• Older people may experience discomfort with exposure to light that is rich in blue light.
• Either discomfort glare or disability glare can be temporarily caused by vehicle LED lights, and particularly daylight running lights and headlights.
• Light sources that emit more short-wavelength light, as do some types of LEDs, will have a larger effect on the circadian rhythms at equal optical radiance, duration, and timing of exposure.