light Flashcards
What are the two types of light?
Natural (Sun, sky) and Artificial (manmade-bulbs, lamps)
This distinction is important for understanding different lighting applications.
What does the Lumen method calculate?
The number of lamps required to meet a specific illuminance level
Reflection, room geometry, and maintenance are also considered.
What is the formula for the Lumen method?
N = E.A / F.U.LLF
Where N = number of lamps, E = average illuminance (lux), A = area of working space (m²), F = total luminous output (lumens), LLF = light loss factor, U = utilization factor.
What does the utilization factor indicate?
The proportion of light emitted by the lamp that reaches the surface of interest
It ranges from 0.0 to 1.0 and is affected by room geometry and reflectance.
How do you find the utilization factor?
Determine the height of fittings above the working plane, assuming it to be 0.85M if unknown
This assumption aids in calculations for lighting design.
What is the formula for the room index (RI)?
RI = L x W / Hm (L + W)
This calculation is used to look up the utilization factor from a reference book.
What is the light loss factor associated with?
Maintenance programs addressing how light is lost
Factors include bulb failures, time/usage degradation, and dirt on surfaces.
What is the typical space to height ratio for lighting?
Around 1.5
This ratio helps determine efficient spacing between lamps.
What is light?
A form of electromagnetic radiation
Energy is radiated by atomic processes, leading to a range of colors.
What is the range of visible wavelengths for electromagnetic radiation?
About 680nm - 760nm
When all wavelengths are perceived together, the brain interprets it as white light.
What is a solid angle?
A measure of how space around a point can be divided in three dimensions
The standard SI unit is steradian.
How is one steradian defined?
The solid angle at the center of a sphere that covers an area equal to the size of a radius squared
This definition is crucial for understanding light distribution.
What is the formula for illuminance on a surface?
e = f / A
Where e = illuminance, f = total flux, A = area of surface.
What do the CIBSE codes of interior lighting provide?
Minimum standards of illuminance for different rooms
Compliance is necessary for building approval.
What is luminance?
A measure of the ability of a light source or reflecting surface to produce brightness
It affects how an object appears based on emitted or reflected light.
What is the formula for luminance?
L = luminous intensity in a given direction / area of source as seen from that direction
The unit is candela per square meter.
What is the equation for illuminance intensity?
I = F / W
This equation relates luminous flux to the area over which it spreads.
