Light 1 - Photometry, Perimetry

What is the core unit of radiometry?

The core unit of radiometry is the Watt (W).

What does radiometry measure?

Radiometry measures the power of electromagnetic radiation.

What is the radiometric unit of energy?

The radiometric unit of energy is the Joule (J).

What is the relationship between Watts and Joules?

1 Watt (W) equals 1 Joule per second (1 J/s).

What is radiant flux or radiant power?

Radiant flux or radiant power is the rate at which energy flows from a point source and is measured in Watts.

What is flux density in radiometry?

Flux density is the rate at which energy flows through a unit area and is measured in W/m².

What is photometry?

Photometry is the measurement of the effect electromagnetic radiation has on human vision.

What is the core unit of photometry?

The core unit of photometry is the lumen (lm).

How is photometry related to radiometry?

Photometry is derived from radiometry.

What is luminous power?

Luminous power is the rate at which energy is transferred and emphasizes the lumen as a measure of energy tailored to human eye sensitivity.

What is luminous flux?

Luminous flux is the rate at which visible light energy flows and describes the human-visible light emitted by a source.

What wavelength corresponds to the peak of the human photopic luminosity function?

555 nm (yellow-green light) corresponds to the peak of the human photopic luminosity function V(λ).

How many lumens per Watt are defined at 555 nm?

683 lumens per Watt are defined at 555 nm.

What source emits 1 lumen of pure 555 nm light?

A source emitting 1/683 Watt of radiant power at 555 nm emits 1 lumen.

What is the candela historically based on?

The candela was historically based on the light given out by a standard candle.

What photometric quantity does the candela measure?

The candela measures luminous intensity.

What directional component is incorporated into the candela?

The candela incorporates the steradian as a directional component.

What is a steradian?

A steradian is the solid angle subtended by a circular cone of 65.54 degrees that cuts out an area equal to r² on a sphere surface.

What fraction of a sphere’s surface area does 1 steradian represent?

1 steradian represents 1/12.56636 of a sphere’s surface area.

What is the relationship between lumens and candelas?

1 lumen per steradian equals 1 candela (1 lm/sr = 1 cd).

How many lumens does a 1 candela light source emit in all directions?

A 1 candela light source emits approximately 12.57 lumens in all directions.

Why was the value 683 lumens/Watt chosen?

The value was chosen because the standard spermaceti candle emitted about 1/683 W per steradian at 555 nm.

What law defined the standard candle in the United Kingdom?

The United Kingdom’s 1860 Metropolitan Gas Act defined the standard candle and its candlepower.

What material was used in standard candles?

Standard candles were made from pure spermaceti.

What is spermaceti?

Spermaceti is a waxy fat found in the head cavity of sperm whales.

How much spermaceti was used in the standard candle?

The standard candle used 76 g of pure spermaceti.

At what rate did the standard candle burn?

The standard candle burned at a rate of 7.8 g/hr.

What advantages did spermaceti candles have?

Spermaceti candles produced clear white light, minimal smoke, soot, and odor, and had a high melting point that maintained shape in summer.

Who first proposed the lumen?

André Blondel first proposed the lumen in 1894.

What was Jules Louis Gabriel Violle’s candle unit based on?

Violle’s candle unit was based on the light emitted by 1 cm² of platinum at its melting point of 1042° K.

How was the lumen originally defined relative to Violle’s unit?

The lumen was originally defined as 1/60 of Violle’s unit.

When were the candela and lumen adopted into the SI system?

The candela and lumen were adopted into the SI system in 1948.

How was the modern candela defined in 1979?

The modern candela was defined as 1/683 Watt per steradian at 555 nm.

What are the main photometric quantities discussed in the lecture?

The main photometric quantities are luminous power, luminous flux, luminous intensity, luminous efficacy, luminous efficiency, luminance, and illuminance.

What is luminous efficacy?

Luminous efficacy is the ratio of luminous flux to radiant flux and is measured in lumens per Watt (lm/W).

What is luminous efficiency?

Luminous efficiency is normalized luminous efficacy relative to 683 lm/W at 555 nm and is unitless.

What does luminous efficiency yield?

Luminous efficiency yields the photopic luminosity function.

What is the luminous efficacy of 555 nm light?

The luminous efficacy of 555 nm light is 1 lm/W in normalized efficiency terms.

What is the luminous efficacy of 650 nm light?

The luminous efficacy of 650 nm light is approximately 0.1 lm/W in normalized efficiency terms.

How can luminous flux at a given wavelength be calculated?

Radiant flux multiplied by luminous efficiency gives luminous flux in lumens.

What are the different photopic luminosity function curves shown in the lecture?

The lecture showed the CIE 1931 curve, the Judd-Vos modified curve, and the Sharpe, Stockman, Jagla & Jägle 2005 curve.

What color represented the scotopic luminosity function in the lecture figure?

The scotopic luminosity function was shown in green.

What physical law was associated with color temperature in the lecture?

Wien’s displacement law was associated with color temperature.

How is luminous efficacy alternatively defined for commercial light sources?

Luminous efficacy can also be defined as the ratio of luminous flux to input power.

How is luminous efficacy commonly used commercially?

It is used to describe how many lumens are output for a given Watt input by a light source.

Why are incandescent bulbs considered inefficient in efficacy despite being thermally efficient?

Incandescent bulbs emit much of their energy as infrared radiation, which does not contribute to visible light.

What percentage of incandescent bulb energy loss is due to heat conduction and convection?

Approximately 20% of energy loss in incandescent bulbs is due to heat conduction and convection.

What is the approximate luminous efficacy of incandescent bulbs?

Incandescent bulbs have a luminous efficacy of about 20 lumens/Watt.

What is the approximate luminous efficacy of a good LED?

A good LED has a luminous efficacy of about 80 lumens/Watt.

What is the theoretical maximum luminous efficacy?

The theoretical maximum luminous efficacy is 683 lumens/Watt for narrow-band 555 nm light.

What percentage of the theoretical maximum luminous efficacy do incandescent bulbs achieve?

Incandescent bulbs achieve about 3% of the theoretical maximum luminous efficacy.

What is luminance?

Luminance is the amount of light coming off a surface in a given direction and is measured in candelas per square meter (cd/m²).

What is the conversion between foot-lamberts and cd/m²?

1 foot-lambert equals 3.426 cd/m².

What is a Lambertian surface?

A Lambertian surface is a perfectly diffusing matte surface with constant luminance regardless of viewing angle.

What are characteristics of a perfectly reflecting and diffusing surface?

A perfectly reflecting and diffusing surface has constant luminance regardless of viewing angle.

How does luminance behave on a specular surface such as a mirror?

Luminance on a specular surface varies with viewing direction.

What is illuminance?

Illuminance is the amount of light falling on a surface and is measured in lux.

What are the units of illuminance?

Illuminance is measured in lumens per square meter (lux).

What is brightness?

Brightness is the subjective perception of light intensity.

What is perimetry?

Perimetry is a clinical technique used to map out the visual field.

What are the standard forms of perimetry discussed in the lecture?

The standard forms discussed were Goldmann kinetic perimetry and Humphrey static automated perimetry.

What diseases is perimetry commonly used to monitor?

Perimetry is commonly used to monitor glaucoma, macular degeneration (MD), and retinitis pigmentosa (RP).

Why is Goldmann perimetry considered kinetic?

Goldmann perimetry is kinetic because a spot of light is moved from the periphery toward the center until it is detected.

How is the target presented in Goldmann kinetic perimetry?

A spot of light is shone onto a hemispheric Lambertian surface and moved inward from the periphery until detected.

What observations are made during Goldmann kinetic perimetry?

The examiner notes where the target becomes visible and whether it disappears afterward.

What stimulus variables can be altered in Goldmann perimetry?

Spot size and brightness can be varied.

Why is Humphrey perimetry considered static?

Humphrey perimetry is static because the spot remains at a fixed location while brightness increases until detected.

How does a patient respond during Humphrey perimetry?

The patient presses a button when the light spot is detected.

What variables are manipulated in Humphrey perimetry?

Both spot brightness and background brightness are varied.

What outdated luminance unit is used in perimetry?

The apostilb (asb) is an outdated luminance unit used in perimetry.

From what measurement system does the apostilb originate?

The apostilb originates from the centimeter-gram-second (CGS) system of measurements.

From what larger unit is the apostilb derived?

The apostilb is derived from the stilb (sb).

What is the mathematical relationship between apostilbs and stilbs?

1 asb = 1/π × 10⁻⁴ sb.

What is the relationship between apostilbs and cd/m²?

π asb equals 1 cd/m².

What is a stilb?

A stilb is a luminance unit equal to 1 cd/cm².

Who coined the term stilb?

André Blondel coined the term stilb.

Why was the apostilb retained in modern perimetry?

It was retained to maintain continuity with Hans Goldmann’s revolutionary perimeter from 1945.

What is the standard background luminance used in modern perimetry?

The standard background luminance is 31.5 asb, equivalent to 10 cd/m².

How is threshold spot intensity typically expressed in perimetry?

Threshold spot intensity is expressed in decibels below the brightest stimulus.

What luminance corresponds to 0 dB in perimetry?

10,000 asb corresponds to 0 dB.

What was the maximum brightness of the Goldmann perimeter?

The maximum Goldmann perimeter brightness was 1,000 asb.

What luminance corresponds to 10 dB in perimetry?

1,000 asb corresponds to 10 dB.

What luminance corresponds to 20 dB in perimetry?

100 asb corresponds to 20 dB.

What is the dimmest luminance discussed in the lecture for perimetry?

The dimmest luminance discussed was 0.1 asb, corresponding to 50 dB.

Who produced Hans Goldmann’s perimeter in 1945?

Haag-Streit produced Hans Goldmann’s perimeter in 1945.

When did the Humphrey Field Analyzer become commercially available?

The Humphrey Field Analyzer became commercially available in 1984.

Who produced the Humphrey Field Analyzer in 1991?

Carl Zeiss produced the Humphrey Field Analyzer in 1991.

Who produced the Tübinger perimeter in 1959?

Oculus produced the Harms & Aulhorn Tübinger perimeter in 1959.

What was unique about the Tübinger perimeter?

The Tübinger perimeter was the first perimeter designed for static threshold testing and combined static and kinetic perimetry.

Was the original Tübinger perimeter automated?

No, the original Tübinger perimeter was still manual.

When did the Tübinger perimeter become automated?

The Tübinger perimeter became automated in 1980.

Why did the Humphrey perimeter overtake the Oculus perimeter?

The Humphrey perimeter overtook the Oculus perimeter because of its age-matched normative database, proprietary adaptive testing algorithms, and brighter background that better probed complete scotomas.

Who was Elfriede Aulhorn?

Elfriede Aulhorn was the first female full professor of ophthalmology in Germany.

What structures are included in the ocular anatomy review?

The ocular anatomy review included the ciliary muscle, lens zonules, cornea, iris, pupil, anterior pole, anterior segment, lens, Schlemm’s canal, posterior segment, sclera, choroid, retina, fovea, foveola, posterior pole, optic nerve, central retinal artery/vein, and optic disc.

What is another name for the lens zonule?

The lens zonule is also called the suspensory ligament or Zonule of Zinn.

What retinal layers were labeled in the retinal anatomy review?

The retinal anatomy review labeled the inner limiting membrane, outer limiting membrane, nerve fiber layer, inner plexiform layer, and outer plexiform layer