EIB- Lighting

what is light?

radiant energy that is capable of exciting the retina and producing a visual sensation

what is visible light?

part of the electromagnetic spectrum from 38- to 780 nm

how does light interact with the eye?

enters the eye through the pupil, is focused through the retina, and transmitted to the brain via the optic nerve

what are the light receptor cells?

rods and cones

what are cones?

responsible for the high-level daytime photopic vision

what are rods?

responsible for the low-level nighttime or scotopic vision

what speed do waves travel at?

the speed of light, c

what is the relationship between wavelength and frequency?

c = f x gamma when c = 3*10^8 m/s

what is rectilinear propagation?

light travels in straight lines in vacuum

what is reflection?

light striking a smooth surface turns back into the original medium

what is refraction?

light bends when entering a transparent medium

what is transmission?

light passes through an object

what is absorption?

object can absorb part or all of the incident light, usually by converting it into heat

what is selective absorption?

materials which absorb some wavelength while transmitting others

what is diffusion?

when light strikes a rough surface and the light is either reflected or transmitted in many different directions at once

what are the types of reflection?

1. specular reflection

2. spread reflection

3. diffuse reflection

what is specular reflection?

occurs when light is reflected away from the surface at the same angle as the incoming light, like in a mirror

what is spread reflection?

occurs when an uneven surface reflects light at more than one angle, but the reflected angles are all more or less the same as the incident angle

what is diffuse reflection (Lambertain scattering)?

occurs when a rough or matte surface reflects the light at many different angles

what does refraction depend on?

the incident angle (theta) and the refractive index of the material (n)

what is the index of refraction?

n = speed of light in vacuum/ speed of light in the material = c/v

what is luminous flux (phi)?

the quantity of light emitted by a light source (unit: lumen)

what is luminous efficiency?

the ratio of the luminous flux to the electrical power consumed, measure of the light source's economic efficiency

what is luminous intensity (I)?

describes the quantity of light that is radiated in a particular direction (unit: candela)

what is luminous intensity useful for?

measuring directive lighting elements such as reflectors

what is a steradian (sr)?

a solid angle necessary for working with luminous flux that is subtended at the center of a sphere by an area equal to the square of its radius

what is illuminance (E)?

the quantity of luminous flux falling on a surface, it decreases by the square of the distance (inverse square law) (unit: lux lx)

what is a lux?

the illumination of one lux occurs when a flux of one lumen falls on an area of one square meter

what is luminance (L)?

specifies the brightness of a surface and essentially dependent on its reflectance (finish and color) (unit: cd/m^2)

what is the only basic lighting parameter that is perceived by the eye?

luminance

how is luminous intensity represented?

by the luminous intensity distribution curve or polar curves

how is illuminance represented?

isolux curves (projected values on the same plane and line links)

how is luminance represented?

isoluminance curves (values measured in candelas per square meters)

what is the color temperature?

a numerical measurement of its color appearance

what is the color temperature based on?

the principle that any object will emit light if it is heated to a high enough temperature and that, as temperature increases, the color of that light will change along with the temperature

what is the color rendering index (CRI)?

a number between 1 and 100 used to describe the ability of a lamp to accurately render all the colors in the lighted space

what is the correlated color temperature (CCT)?

temperature, describes the overall color appearance of a lamp or white light source (Kelvins)

what is glare?

difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps

what is glare caused by?

direct:

• luminaires w/out glare control

• very bright surfaces

reflected:

• reflective surfaces

• incorrect luminaire arrangement

• incorrect workstation position

what is the effect of glare?

direct and reflected:

• loss of concentration

• more frequent mistakes

• fatigue

what is the remedy for glare?

direct:

• luminaires with limited luminance levels

• blinds on windows

reflected:

• matching luminaire to workstation (layout)

• indirect lighting

• matte surfaces

what is the unified glare rating?

the rating method used to evaluate glare based on all the luminaires in the system that contribute to the sensation of glare