LIGHTING Flashcards
What is veiling reflection?
These are reflections that obscure flat surfaces because the light is on them directly…?
Miles to a gallon is to lumens to ____?
Watts
What is the color rendition index?
A measure of how well light shows true color, usually employed with artificial lighting… The best possible rating is 100 where there are no colors missing
If there was a 1 ft.² in the air at a distance of 1 foot from a one candlepower source what would be the amount of light flowing through that Square?
One lumen
What Is the flow of light called?
Flux
What is the symbol and formula for illumination?
The letter E
E = F / A
Where
F is flux
A is area
What is a lumen?
A lumen is a unit of a luminous flux
Okay so there’s illumination. Now what is luminance?
How bright does it look… That is it’s luminance … And how reflective it is
but it also may refer to the amount of light passing through a translucent surface … But a translucent surface will have it’s luminance shown on the far side not the near side
A perfectly reflective surface exposed to an illumination of one footcandle would have a luminance of how many footlamberts?
One footlambert
What is the inverse square law for light?
If the source of light can be approximated as a point, the flux, and resultant illumination is inversely proportional to the square of the distance from the surface.
When you’re 10 feet away, what is the intensity of the 1600 candlepower light?
16 foot candles
Calculate the footlamberts I have a 16 foot candle illuminants on a surface with the reflectance of 0.75
L = 16 fc x 0.75 = 12c
What is a typical lumen output and lifetime of how many hours for an incandescent light?
15 to 18 lm per watt, and a lifetime of around 2000 hours
How big is a 100 W A–19 bulb?
Uses 100 W, and it is 19 inches times 1/8 of an inch in diameter … Or 2.375” dia.
What does the ballast do in a fluorescent lamp?
Controls the voltage in the current
Fluorescent color produces the most to lumens per watt, but what is it’s disadvantage?
Cool white is the most efficient, but it makes people’s skintones look really ugly
Efficiency an average lifetime of a fluorescent light is…
60 to 80 lm per watt, 10,000 hours
What were the first high intensity discharge lamps? What was wrong with them and what improved them?
Mercury vapor lamps. They produce a bluish light that makes people look unhealthy. Adding phosphors helps. This is the mercury vapor deluxe… 24,000 hours and 50 lm per watt
How did the metal halide improve on the mercury vapor lamp? What’s the efficiency and lifetime?
It shifted the color and improve the efficiency to 80 lm per watt, but it dropped a lifetime down to 10,000 hours… Just like a fluorescent lamp
What is the most efficient of the HID lamps?
High pressure sodium with an efficiency of 110 lm per watt… With a 24,000 our life expectancy, the same as the mercury vapor lamp
… Well low pressure sodium is even more efficient with a longer life time but it looks terrible and there is no color addition at all
What is the formula for the point grid method?
E = I * cos(x/d²)
Where:
E = illumination at the receiving source I = candlepower if source... intensity at the source when viewed from the direction of the receiving surface x = angle between a perpendicular vector (the normal) to the receiving surface and a line from the source to the surface d = distance from the source to the surface
What are candlepower distribution curves?
These plot the light intensity given off by a fixture
If all the light goes up what kind of fixture is it?
An indirect fixture
What is Abney’s law?
Light on the surface is the sum of the light from all of its sources, and can be expressed by repeating the point grid formula
