Electrical & Lighting

Question 1

what is Ohms law?

Answer 1

I = V/R (Volts/ resistance) Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

Question 2

what is the voltage over two legs of a 3phase (4wire) system?

Answer 2

208v

Question 3

what is the voltage over two legs of a 2 phase (3wire) system?

Answer 3

240v

Question 4

what are the advantages of using a 277v system?

Answer 4

smaller wiring, smaller feeders, smaller conduit, smaller switch gear.

Question 5

what are the 3 types of transformers?

Answer 5

dry
oil filled
silicone

Question 6

what is the appropriate spacing for elec outlets?

Answer 6

12’ horizontally, 4’ in a kitchen horizontally. outlets within 6’ of a sink must be GFCI.

Question 7

what are three things that can happen to light when it hots a surface?

Answer 7

Transmitted (glass), Reflected (mirror) or absorbed (concrete).

Question 8

what is the transmittance or coefficient of transmission?

Answer 8

its expressed as a %, its the ratio of the total transmitted light to the total incident light.

Question 9

what are the two types of glare?

Answer 9

DIRECT: as result when a light source in the field of vision causes discomfort & interference with a visual task. Typ 45deg from the ceiling and the light fixture.

REFLECTED: occurs when a light source is reflected from a viewed surface into the eye.

Question 10

what is lighting efficiency?

Answer 10

the ratio of luminous flux emitted ti the total power input to the source.

Question 11

what is the approx color temp of a mercury vapor lamp?

Answer 11

5500k

Question 12

what is the approx color temp of a metal halide lamp?

Answer 12

3000k to 4500k

Question 13

what is the approx color temp of a high pressure sodium lamp?

Answer 13

2800k

Question 14

in a ‘A’ lamp designation what does the number following the ‘A’ stand for?

Answer 14

the diameter of the bulb at the widest point in 8th of an inch. A-20 = A base & 20/8ths of an inch

Question 15

what types of lamps are HID (High Intensity Discharge)

Answer 15

mercury vapor, metal halide & haigh/ low pressure sodium

Question 16

what is the color temperature of daylighting?

Answer 16

6500k

Question 17

what is the Coefficient of Utilization? (CU)

Answer 17

it represents the fact that not all of the lumens produced by the lamps reache the work surface. the CU is a number from .1 to 1.0 that depends upon the design of the fixture and the characteristics of the room

Question 18

what is the zonal cavity method?

Answer 18

# of fixtures x lamps per fixture
Footcandles = x lumens per lamp x CU x LLF/
(maintained) area in square feet

Question 19

What is luminous flux?

Answer 19

All the radiated power emitted by a light source and perceived by the eye is called luminous flux. The unit of measurement is the lumen (lm).
The visible radiated power of a light source is not expressed in watts but in lumens since the sensitivity of the human eye differs according to the particular wavelength.

Question 20

what is the daylight factor?

Answer 20

0.2 x (window area / floor area)