Luminance and illuminance sound like similar terms in the lighting world but have vastly different meanings. Find out the difference here. (c) the ratio of interior daylight illuminance to exterior daylight The relationship between illuminance and luminance for an opaque surface is. colors are always perceived in relationship to the colors around them, and to the .. have the same “brightness” if exposed to the same illumination. The.
The principal planes of the lens are represented as lying at PP and at PP', while the entrance and exit pupils are designated as being at NP and XP, respectively, and the principal focal lengths are L and L'. The point P may be self-luminous or may be illuminated by reflected light. In either case it will illuminate the entrance pupil of the lens NP with an intensity inversely proportional to the square of the distance between P and R, the latter being in the plane of the entrance pupil, and directly proportional to its luminous intensity I.
Let the distance between P and R be X. The distance X may be considered as being made up of two components. The negative sign is required because of the inversion of the image. The second component of the distance X is the distance LR from the plane of the principal focus to the plane of the entrance pupil. The intensity of the image at P' is inversely proportional to the area of the image.
Of the light incident upon the lens, some is absorbed, but a greater part is reflected from the lens surfaces, especially if these are uncemented. The quantity of the emerging light is always less than that incident upon the system and is proportional to the incident light and the transmission of the lens system T.
Consequently I' is proportional to T. Having discussed briefly the separate factors which influence the intensity of the image, we may now combine the separate effects. For objects considerably off the optical axis, and especially when the view angle is large, the intensity of the image at a corner of the plate may vary considerably from that given by Eq. By definition the f-number of a lens is the ratio of the focal length to the diameter of the aperture.
When this substitution is made, we obtain: This equation states that the intensity of the image is proportional to the intensity of the original object, proportional to the transmission of the lens system, inversely proportional to the square of the f number, and inversely proportional to the square of the linear magnification plus one. Image Brightness as Function of Filter A filter is frequently employed in photography to increase contrast, to produce desirable pictorial effects, or to distinguish between tone rendition of various colors.
The property inherent in all filters is absorption of a portion of the spectrum to which the photographic emulsion is sensitive, and it thereby decreases the effective intensity of illumination on the photographic material.
Because of this reduction of luminous intensity, the exposure must be increased. The filter factor, for a particular filter, light source, and photographic emulsionis a measure of the required increase in exposure and is also a measure of the extent to which it reduces the quantity of light reaching the photographic material. Failure of the reciprocity law is not of serious consequence in most branches of practical photography, and, for a first approximation, may be neglected.
A fluorescent circuit that ignites the lamp instantly with a very high starting voltage from the ballast. Instant start lamps have single-pin bases. The peak lamp current divided by the RMS average lamp current.
An LCCF of 1. A factor that represents the reduction of lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation.
The LLD factor is a dimensionless value between 0 and 1. A fluorescent fixture; usually a 2' x 4' fixture that sets or "lays" into a specific ceiling grid. Abbreviation for light emitting diode. An illumination technology used for exit signs. Consumes low wattage and has a rated life of greater than 80 years.
Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic. Factors that allow for a lighting system's operation at less than initial conditions. These factors are used to calculate maintained light levels. LLFs are divided into two categories, recoverable and non-recoverable.
Examples are lamp lumen depreciation and luminaire surface depreciation. The total costs associated with purchasing, operating, and maintaining a system over the life of that system.
Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodized aluminum louvers used in parabolic fluorescent fixtures. Essentially, an uncorrected ballast power factor of less than 0. A low-pressure discharge lamp in which light is produced by radiation from sodium vapor. Considered a monochromatic light source most colors are rendered as gray. A lamp typically compact halogen that provides both intensity and good color rendition.
Lamp operates at 12V and requires the use of a transformer. A relay magnetically-operated switch that allows local and remote control of lights, including centralized time clock or computer control. A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp. A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps, and connect the lamps to a power source.
Also called a fixture. The ratio of total lumen output of a luminaire and the lumen output of the lamps, expressed as a percentage.
For example, if two luminaires use the same lamps, more light will be emitted from the fixture with the higher efficiency. A photometric term that quantifies brightness of a light source or of an illuminated surface that reflects light.
It is expressed as footlamberts English units or candelas per square meter Metric units.
Illuminance - Wikipedia
The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square meter.
One lux equals 0. Refers to light levels of a space at other than initial or rated conditions. This terms considers light loss factors such as lamp lumen depreciation, luminaire dirt depreciation, and room surface dirt depreciation.
A type of high intensity discharge HID lamp in which most of the light is produced by radiation from mercury vapor. Emits a blue-green cast of light.
Available in clear and phosphor-coated lamps.
Luminance and Illuminance
A type of high intensity discharge HID lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. A low-voltage quartz reflector lamp, only 2" in diameter. Typically the lamp and reflector are one unit, which directs a sharp, precise beam of light. A reference direction directly below a luminaire, or "straight down" 0 degree angle.
Abbreviation for National Electrical Manufacturers Association. Abbreviation for National Institute of Standards and Technology. Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared or other type. A term referring to the components of a light fixture such as reflectors, refractors, lenses, louvers or to the light emitting or light-controlling performance of a fixture.
A parabolic aluminized reflector lamp. An incandescent, metal halide, or compact fluorescent lamp used to redirect light from the source using a parabolic reflector. Lamps are available with flood or spot distributions. A popular type of fluorescent fixture that has a louver composed of aluminum baffles curved in a parabolic shape. The resultant light distribution produced by this shape provides reduced glare, better light control, and is considered to have greater aesthetic appeal.
A metallic coated plastic louver made up of small squares. Often used to replace the lens in an installed troffer to enhance its appearance. The paracube is visually comfortable, but the luminaire efficiency is lowered. Also used in rooms with computer screens because of their glare-reducing qualities.
A light sensing device used to control luminaires and dimmers in response to detected light levels.
A photometric report is a set of printed data describing the light distribution, efficiency, and zonal lumen output of a luminaire. This report is generated from laboratory testing. The ratio of AC volts x amps through a device to AC wattage of the device.
Some utilities charge customers for low power factor systems. A compact fluorescent lamp with a double twin tube configuration.
Interference to the radio frequency band caused by other high frequency equipment or devices in the immediate area. Fluorescent lighting systems generate RFI. This ballast quickly and efficiently preheats lamp cathodes to start the lamp. Uses a "bi-pin" base. A ratio of room dimensions used to quantify how light will interact with room surfaces.
A factor used in illuminance calculations. The ratio of light reflected from a surface to the light incident on the surface.
Reflectances are often used for lighting calculations. The part of a light fixture that shrouds the lamps and redirects some light emitted from the lamp. A device used to redirect the light output from a source, primarily by bending the waves of light. The term used to describe the doorframe of a troffer where the lens or louver lies above the surface of the ceiling.
The ability of a ballast to hold constant or nearly constant the output watts light output during fluctuations in the voltage feeding of the ballast. A device that switches an electrical load on or off based on small changes in current or voltage.
Refers to upgrading a fixture, room, or building by installing new parts or equipment. An illumination technology using phosphor-coated glass tubes filled with radioactive tritium gas.Lighting - Camera Animation Test - Luminance vs Illuminance
The exit sign uses no electricity and thus does not need to be hardwired. Term describing the light reflection characteristics of a material. Some light is reflected directionally, with some amount of scatter. The angle measured from the ceiling plane to the line of sight where the bare lamp in a luminaire becomes visible. Higher shielding angles reduce direct glare. It is the complementary angle of the cutoff angle. A maximum distance that interior fixtures may be spaced that ensures uniform illumination on the work plane.
The luminaire height above the work plane multiplied by the spacing criterion equals the center-to-center luminaire spacing. Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word describes the finish of the material used in some louvers and reflectors. A device used with a ballast to start preheat fluorescent lamps. Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources.
Luminance vs. Illuminance
Sometimes called "strobe effect. Industry standard for a fluorescent lamp that is 12 one-eighths 1 inches in diameter. Other sizes are T10 1 inches and T8 1 inch lamps. A wiring option in which a ballasts is shared by two or more luminaires. This reduces labor, materials, and energy costs.
Also called "master-slave" wiring. A factor used in lighting calculations that compensates for the change in light output of a fluorescent lamp due to a change in bulb wall temperature.
- Luminance vs. Illuminance
It is applied when the lamp-ballast combination under consideration is different from that used in the photometric tests. Type of ballast commonly used with watt and watt straight fluorescent lamps. The term used to refer to a recessed fluorescent light fixture combination of trough and coffer. A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens namely iodine, chlorine, bromine, and fluorinewhich slow the evaporation of the tungsten.