Illumination

Example 1. Light from a Helium-Neon laser has a wavelength of 632 nm. What is the frequency of this wave?

8

-9

3 x 10 m/s

632 x 10 m

cc f f

f = 4.75 x 1014 Hzf = 4.75 x 1014 Hz Red light

The Helium Neon Laser Wavelengthl = 632 nm

Laser

Example 3. What solid angle is subtended at the center of a sphere by an area of 1.6 m2? The radius of the sphere is

5 m.

W

A 1.6 m2

R 5 m

The Steradian

2

A

R

2

2

1.60 m

(5.00 m)

2

A

R

W = 0.00640 srW = 0.00640 sr

Example 4. A 30 cd spotlight is located 3 m above a table. The beam is focused on a surface area of 0.4 m2. Find the intensity

of the beam.

Total flux: F = 4pITotal flux: F = 4pI

FT = 4p(30 cd) = 377 lm W R 3 m

The luminous intensity of the beam depends on .W

2

2 2

0.4 m; 0.0444 sr

(3 m)

A

R

754 lm

0.0444 sr

FI

Beam Intensity:

I = 8490 cdI = 8490 cd

Example 5. A 400-cd light is located 2.4 m from a tabletop of area 1.2 m2. What is the illumination and what flux F falls on

the table?

WR2 2

400 cd

(2.40 m)

IE

R

E = 69.4 lxIllumination:

Now, recalling that E = F/A, we find F from:

F = EA = (69.4 lx)(1.20 m2) F = 93.3 lm

CRITERIA IN MANUAL CALCULATIONCalculation by Lumen Method:

The average illuminance produced by a lighting installation or the number of luminaires required to achieve a specific average illuminance, can be calculated by means of utilization factors. The average illuminance Es over a reference surface s can be calculated from the “lumen method” formula.

F x n x N x MF x UFs

Es = ------------------------------

area of surface s

where: F is the initial bare lamp flux (lumens, lm)

n is the number of lamps per luminaire

N is the number of luminaires

Ufs is the utilization factor for the reference surface s

MF is the maintenance factor (dirty: 0.7, normal: 0.8, clean: 0.9)

CRITERIA IN MANUAL CALCULATION

Sample Problem:

Mr. Cruz wants to light up his new warehouse in Laguna. The warehouse measures 20m x 30m. He wants to mount his luminaires on the trusses 8m above finish floor line. What type of luminaire will he use and how many of those will he purchase?

Given: L = 20m, W= 30m, H = 8m, MF = use 0.8Reflectances (use default) : C = 0.7 W = 0.5 F = 0.2

Solution: To obtain UF, solve for Room Index (RI) = A/(L+W)Hw, RI = 1.5

Required Average Illuminance (Eave) for warehouse as per standard is 100 lux

Solution (cont.):

Since mounting height is 8m, use high bay fixture.From UF table of Thorn High Bay, UF = 0.78

Substituting to equation: F x n x N x MF x UFsE = ------------------------------

A (100)(600)

N = ------------------------------- (27500)(1)(0.8)(0.78)

N = 3.49, use 4 sets 250W SON-T high bay lighting fixtureChecking the lighting level, E = 114.4 lux