# RKS: LIGHT & LUMINATION - Enlightening About Brightness Intensities
# RKS: LIGHT & LUMINATION
ENLIGHTENING ABOUT BRIGHTNESS INTENSITIES
RKS / 2025-2026 / Ser 8 / Blog 3
1st December 2025
REVEALING SEEING DYNAMICS
THE RETINA & ILLUMINATING
Dear Reader,
Seeing light is taken for granted. Seeing images, objects and beauty is what the eyes are meant for. However, the mechanisms that lie behind what makes one see and perceive are indeed intriguing and worth understanding to appreciate the miracle of sight that has been bestowed to living beings.
EYE - RETINA - VISION
There are three layers of tissues in the eye and retina is the innermost and forms the curtain.
Fig: Layers of eye.
The retina of the eye has rods, cones and intrinsically photosensitive retinal ganglion cells (ipRGCs). All these 3 types are sensory nerve cells (neurons) that sense light and also called photoreceptors. These specialized neurons detect light and convert it to electrical signals which the brain interprets.
Fig: Cells of retina.
Rods are 500 to 1,000 times more sensitive to light than cones. The retina of one eye has approximately 120 million rods, 6 million cones but only 4,000 – 7,000 ipRGCs in humans.
FUNCTIONS OF PHOTORECEPTORS
Rods and cones are photoreceptors responsible for image formation, while ipRGCs are involved in non-image-forming vision:
- RODS: These cells enable vision in low-light conditions - scotopic vision or night vision.
- CONES: These cells enable photopic vision, also known as day vision, which is the ability to see in bright light. Unlike scotopic vision (night vision), which relies on rod cells, photopic vision allows for color differentiation and provides a higher visual acuity.
- ipRGCs: These photoreceptors primarily mediate functions like circadian timing and pupillary light reflexes.
Thus, melatonin secretion and sleep / alertness cycle is influenced by ipRGCs' ability to sense light without relying on rods and cones.
HOW LIGHT - TO - VISION?
Light is described by a wave-particle duality, meaning it has properties of both waves and particles. Light waves are a form of electromagnetic radiation, consisting of oscillating electric and magnetic fields that travel through space at the speed of light. They are characterized by their wavelength and frequency, which determine properties like color and energy. The tiny packages of energy in light waves are called photons.
The membrane of the retinal cells contain proteins called opsins which play a role in absorbance of photons which in turn stimulates rods, cones and ipRGCs. There are 3 known human retinal opsins:
- Melanopsin – present in ipRGCs
- Rhodopsin – present in rods
- Iodopsins – present in cones
There are 3 iodopsin varieties in cones:
- S-cone opsin – detects light of short wavelengths (blue)
- M-cone opsin – detects middle of short wavelengths (green)
- L-cone opsin – detects light of long wavelengths (red)
When eyes are open the rods detect light whilst the cones differentiate colours. The signals from the rods and cones are deflected to ipRGCs. Light also strikes the melanopsin and the ipRGCs directs this as well as the signals received from rods – cones to the back of brain (optic lobe) via a special optic nerve for the light-emitting image to be interpreted and recognized.
LIGHT & SLEEP CYCLE
Melanopsin can be described as a type of light meter in the retina that is responsible for adjusting our circadian rhythm. Melanopsin is highly sensitive to blue light, and this sensitivity is taken into account in Melanopic EDI (Equivalent Daylight Illuminance).
Melanopic EDI is a method used to explain how much a light source affects the circadian rhythm of humans – including the sleep-wake cycle.
Melanopic EDI, which is high in the morning and wanes towards the evening, causes melanopsin to send a signal to the brain that it is still daytime. This prevents the secretion of the 'hormone of darkness', melatonin, which plays a crucial role in onset of sleep cycle. Thus, there is high melanopic EDI during the daytime and low to no melanopic EDI at night.
During the daytime the melanopic EDI is 250 lux whilst maximum of 10 lux is recommended during the hours leading to bedtime.
LUX & WATTS
LUX
Lumen and lux (lx) were first defined in the 13th century by Bartholomew of Bologna, an Italian theologian, in the “Tractatus de luce”. One lumen is equivalent to one candle's worth of light.
One lux (Latin for “light”) is the amount of illumination provided when one lumen is evenly distributed over an area of one square metre. In 1932, Weston produced the first direct-reading meter which measured light in footcandles. A foot-candle is a non-SI (International System) unit of illuminance or light intensity and equals to one lumen per square foot.
WATTS
The watt, a unit of power in the International System of Units (SI), was named after James Watt, a Scottish inventor and engineer. One watt is equal to one joule of work performed per second.
One joule is the energy transferred when a force of 1 newton causes a displacement of 1 meter in the direction of the force. One newton is, on the other hand, the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.
Watts was an indicator of how bright the light is in earlier days. However, lights have gotten much more energy efficient with the introduction of LEDs (light-emitting dioides) and CFL’s (compact fluorescent lamp), so now one cannot tell how bright a light is based on watts alone.
LUMEN vs WATTS
Lumens measure the amount of visible light a bulb emits, while watts measure the power it consumes. Higher lumens mean brighter light, while watts indicate how much electricity the bulb uses.
Table: Conversion of watts to lumen equivalents.
If buying a light source based on brightness, using lumens proves a better guide to decision-making.
KELVIN COUNT
The Kelvin temperature scale was developed by Lord Kelvin, also known as William Thomson. However, Kelvin is also a measurement of light color. The Kelvin scale is thus a unit of temperature and color, and it ranges from 1,000 to 10,000 kelvins (K).
Fig: Colour of light with Kelvin Count.
The higher the Kelvin count the “cooler”, or more blue, the light color. The lower the Kelvin count the “warmer”, or more red, the light color.
Color temperatures over 5,000 K are called "cool colors" (bluish), while lower color temperatures (2,700-3,000 K) are called "warm colors" (yellowish). Red light generally falls within the lower Kelvin temperature range, typically between 1,700 K and 2,700 K.
In the morning and evening the sun is more orange or pink, while in the middle of the day it gives off white or light blue color. These qualities are also in light bulbs, which are measured in Kelvins. The lighting industry uses a color range from 8,000 K to 2,000 K, with 5,000 K being the most commonly used.
SCREENS
Nits and lumens both measure light output, but nits measure the brightness of a specific screen surface [television (TV), mobiles, etc.] whilst lumens quantify the total amount of light emitted by a source, such as a projector. Nits and candelas are both units of luminance, but 1 nit is the same as 1 candela per square meter [cd/m^(2)]. A nit is equivalent to the brightness radiated from a traditional candle per square metre. 1 nit equals 3.426 lumens or 3.14159 lx.
Whilst candelas per square meter is the official SI unit for measuring the brightness of a surface area, nits are a more user-friendly term, especially for electronic displays.
CONCLUSIONS
The recommended maximum ambient melanopic EDI is 1 lx measured at the eye. To achieve 1 lx throughout the room, 20 lumens is necessary.
The recommended lux level for a room depends on its use:
- Living rooms: 100-150 lx
- Kitchens: 250-300 lx
- Bathrooms: 150-300 lx
- Classrooms: 300-500 lx
- Libraries: 500 lx
- Reading: Around 200 lx
- Bedrooms: 60-100 lx
Light intensity significantly impacts human health, with excessive or inadequate exposure having negative consequences. Exposure to artificial light, especially at night, can disrupt circadian rhythms, leading to sleep problems, metabolic issues like obesity and diabetes, and potentially increasing the risk of certain cancers.
The bedroom light source should ideally be:
- Incandescent source: 5-10 watts
- CFL bulb: 1-2 watts
- LED light: 0.5-1 watt
In fact, the sleep environment should be as dark as possible. So ensure bedroom light source lesser than 10 lx such that EDI is as close to zero as possible. This will ensure normal circadian rhythm cycles via the ipRGCs and thus good health.
DR R K SANGHAVI
Prophesied Enabler
Experience & Expertise: Clinician & Healthcare Industry Adviser
-------------------------------------------------------------------------------------
POWERED BY -
# fuzionnutra.com
Prophesied Enabler
Experience & Expertise: Clinician & Healthcare Industry Adviser
-------------------------------------------------------------------------------------
Comments
Post a Comment