24 Questions
What is luminance measured in?
Candela per unit area
What is the unit of measurement for illuminance?
Lux
What is the unit of luminous intensity in the given equation E = I/d²?
Candelas
What is the formula for illuminance (E) if the angle of incidence is not 0°?
E = (I/d²) cos θ
What is the conversion rate between candelas per square inch and foot lamberts?
1 cd/in² = 452 foot lamberts
What is the purpose of glare control?
To prevent glare from entering the glare zone
What is the effect of increasing the distance between a light source and a surface?
The illuminance of the surface decreases
What is the definition of luminance?
The amount of light leaving an object per unit of projected area
Why does a surface held perpendicular to a light source receive more light?
Because the angle of incidence is 0°
What happens to the illuminance when the angle of incidence increases?
The illuminance decreases
What is the range of wavelengths of visible light that the human eye is sensitive to?
380 nm to 750 nm
What is the relationship between lux and foot-candles?
1 lux = 1 foot-candle
What is illuminance?
The amount of light incident on a surface
What is the angle above which a fixture's vertical axis is considered to be in the glare zone?
45°
What is the unit of illuminance in the example problems?
Foot-candles
What is the term for excessive brightness in the field of vision?
Glare
What is the relationship between illuminance and distance according to the inverse square law?
Illuminance is inversely proportional to the square of distance
What is the ratio of reflected light versus the light striking the surface?
Reflectance (ρ)
What happens to the illuminance striking a translucent or transparent body?
It is reflected, absorbed, and transmitted
What happens to the cosine of the angle of incidence when the angle of incidence increases?
The cosine decreases
What is the relationship between Reflectance (ρ), Absorptance (α), and Transmittance (τ) for a translucent or transparent body?
ρ + α + τ = 1.0
What happens to the illuminance striking an opaque surface?
It is reflected and absorbed
What is the term used in the lighting industry to avoid confusion when describing a light source?
Lamp
What is color perception?
The ability to distinguish and interpret different wavelengths of visible light
Study Notes
Light and Lighting Basics
- A polar graph shows the relative luminous intensity, in candela, around a lamp or luminaire.
- Glare is excessive brightness in the field of vision, causing discomfort or temporary loss of vision.
- Glare control requires attention to fixture design, selection, and position to prevent light from entering the glare zone.
Illuminance and Luminance
- Illuminance is the amount of light incident on a surface.
- Luminance is the amount of light leaving an object, relating to how bright it appears to the human eye.
- Luminance can be expressed in candelas per unit area or lumens per unit area.
Units of Measurement
- Candela per square inch (cd/in²), foot lambert, and lambert are units of measurement for luminance.
- 1 cd/in² = 452 foot lamberts, and 1 lambert = 929 foot lamberts = 2.054 cd/in².
Illuminance
- Illuminance is the density of luminous flux striking a surface.
- Units of measurement for illuminance include foot-candles and lux.
Visible Light
- Visible light is part of the electromagnetic radiation spectrum, exciting the retina and producing a visual sensation.
- Wavelengths of visible light range from about 380 nm to 750 nm.
Behavior of Light
- Illuminance is the amount of light incident on a surface.
- Luminance is the amount of light leaving an object.
- Reflectance is the ratio of reflected light to the light striking the surface.
- Transmittance is the ratio of light transmitted through a body to the light illuminating the surface.
- Absorptance is the ratio of the light absorbed to the light striking the surface.
Color Perception
- Color perception is the ability to distinguish and interpret different wavelengths of visible light.
- Artificial and natural light sources are composed of many wavelengths having varying magnitudes.
Characteristics of Artificial Lighting
- A lamp is a device that generates light.
- A luminaire is a complete lighting unit consisting of a lamp, reflector, and other components.
Inverse Square Law
- The inverse square law states that illuminance is inversely proportional to the square of the distance between the source and the plane.
Cosine Law of Incidence
- The cosine law of incidence states that illuminance at a point on a plane is proportional to the cosine of the angle of light incidence.
- The angle of light incidence is measured between the direction of the incident light and the normal to the plane of the surface.
This quiz covers the basics of lighting, including polar graphs and luminous intensity, as well as glare and its effects on vision. It also touches on glare control methods.
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