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April 13

Objective

The objective of the experiment is to determine the reflectance and transmittance of

various materials at different incidence angles.

Introduction

Light has two paths when its directed to any surface. When light hit a surface,

reflection is one possible path. Reflection of light can beat an angle or straight. This is

due to translucency and opaqueness of the material tested. The second possibility is

when light passes through or being absorbed by the surface. Many surfaces gain heat

after absorption of light for a period of time. How a surfaces reacts towards light depends

on the light frequency and the geometric distribution of the light itself.

In addition, reflection is defined as the percentage of light that bounces off a surface at an

angle from the surface. It can be measured using the following formula:

Ρ=Er/Ei = Lr/Li

Where

Lr: Luminance reading for incidence light at different angles.

Li: Luminance reading when light source 45 degrees to panel

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In addition, Transmittance is the passage of light through and across a given medium. The

following equations are used to find the transmittance coefficient.

1) τn= Εn/Ε

2) τθ=Lθ/Ln x τn

Where,

Lθ : Measured luminance when plat is at an angle from light source.

Ln : Measured luminance when light is normal to surface

Εn : Measured illuminance when light is normal to panel.

E : Measured illuminance at a known distance from the light.

Equation 1, is used when incident light being directed normal to the surface.

Equation 2, is used when incident light directed at an angle to the surface.

Equipment used

- Optical bench set up

- Incadesent lightbulb

- Normal light bulb

- Luminance meter

- Illuminance meter

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Procedures

In order to determine the reflectance of opaque materials we alternatively mount

the white and grey panels onto the holder and measure the luminance perpendicularly at

the centre of the panels. To get the reflectance of a glass material, the following steps

should be followed. Setting the light source and the luminance meter at a known angle to

the panel. When the angle of incident reach 45 degrees we start recording data. We place

another glass panel and start recording data by changing the angle from 10 degrees to 80

degrees. Moreover, Transmittance is also recorded using the illuminance meter. First

setting the light source at a known distance to the surface. Then we record the

illuminance at 45 degrees. Next we rotate the panel from 10 degrees to 80 degrees and

record reading.

Data & Results Part 1

Reflection for different panels: (45degrees perpendicular to light source) @ 54 cm;

Material Luminance (Lw) cu/m3 Reflectance

Gray Panel 235.35 0.214

Black Panel 44 0.040

White Panel 1096

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As a result, it is clear that tinted glass reflect much more light than the clear glass does.

From the graph in figure 1, there is a clear gap between curve 1 (red) and curve 2(blue).

Curve one represent the reflection line of the tinted panel, and curve 2 is the clear panel

with respect to different angle of incidence. We can conclude that the tinted panel reflect

most of the light being pointed at and the reflection decreases as the angle of incidence

increase. On the other hand, curve two represent the reflection of clear glass plate, which

clearly shows that light pass through the glass almost completely. This experiment shows

how two types of glass can change in reflection of light by changing its color and

orientation.

Part 3 Data:

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Transparent Panel

Degree 10 20 30 40 50 60 70 80

L (cd/ m^2) 1090 318 161.3 79.8 42.5 35.5 36.6 46.1

Ln (cd/ m^2) 50200 50200 50200 50200 50200 50200 50200 50200

L/Ln (cd/ m^2) 0.0217 0.00633 0.003213 0.001589 0.000846 0.000707 0.00073 0.000918

E (lux) 1324

En (lux) 1095

tn 0.827 0.827 0.827 0.827 0.827 0.827 0.827 0.827

Transmit tance 0.0179 0.00523 0.00265 0.001314 0.0007 0.00058

0.00060 3 0.00076

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Discusion

The Transmittance values of the two glasses panels where close. From the graph plotted

above we can say that when light hit the surface at 45 degree its gets the maximum

transmittance value and maximum reflection. The orientation of the light source to the

glass panel affect the transmittance values. The bigger the angle gets the lower the

transmittance value for both samples. In addition, at angle of 10 degrees, the

transmittance was maximum for both samples. The transmittance values are very close to

each other in both sample for angles bigger than 5o. before 50 degrees the tinted glass

showed much lower than the clear glass.

Sample calculations:

Part 1:

235.5/1096= 0.214

Part 2:

Reflectance: @ 80 degrees = 231/1500= 0.154

Part 3:

Transmittance: @ 80 degrees = L/Ln x tn = 0.0217 x 0.827 = 0.0179

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Conclusion

In conclusion three parts in this experiment where performed, the first part related to the

reflectance of opaque materials. Second part related to the reflectance values of glass

materials and finally last part is related to the light transmission through glass materials at

different angles. Graphs of the results were plotted and showed the different of light

transmittance and reflectance of the various materials.

References

- Bldg 366 lab manual winter 2015.

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Objective

The main objective of this experiment is to measure the direct horizontal and vertical

illuminance from the sun during different times of the day and various times of the year.

Introduction

In the designing phase of buildings, urban and rural areas, special consideration

should be given to the motion and position of the sun in relation to that of a building area.

The earth orbits around the sun at an axis. And it takes 365 days for the earth to make a

full round around the sun.These considerations that should be made constitute and make

up the design tools needed. In this experiment some of these design tools are to be

studied and noted by observing and using the sun’s position and the availability of

sunlight at certain times and days of the month of the year where within the scope of our

experiment we shall be using a simulated model.

The position of the sun seen from a particular place’s surface varies from hour to

hour and season to season as well. Some of the experimental observations we are to take

are the following: solar declination, solar altitude, vertical and horizontal illumination.

Solar declination is the angular distance between the earths equator and the sun, and it’s a

function of the time of the year where n in the following equation represents any day of

the year e.g. n=1=jan 1

δ = 23.45 sin((360/365)*(n +284))

Solar altitude, on the other hand, is a means to describe the position of the sun at any

instant angularly and it is defined by the following equation:

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sinα = sinL sinδ + cosL cosδcosH

where

L = Latitude( Montreals is 45.3 ⁰) and H= Hour angle = 15 *Solar time

Equipment used

- Model 126 Helidon - Light Meter

Procedures

The procedure of the experiment is simple. To start, a light meter is placed on the

surface of a Model 126 Helidon (a model that portrays the sun set and sunrise in different

months of the year and on different times of the day at different latitudes). Then a light

source at a specific angle that represents the latitude (45 degrees of Montreal) and month

of the year and time of the day is turned on. The light meter then measures the

corresponding illuminance level for that particular light configuration that represents the

actual sunlight hitting the earth on that 21st of the month. The procedure of all parts of the

experiment is almost the same. The light meter placement is changed to measure the

vertical and horizontal illuminance. 


Note: All the measurements are assumed to be taken on the 21st day of each month. 





Equations used:

1) Solar Altitude (sin α) = sinL sinδ – cosL cosδ cosH

2) δ = 23.45sin [ 360/365 ( n +284 ) ]

3) H = 15 * solar time

n = number of the day in the year, L = latitude, H= Hour angle

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Discussion

looking at graph 4, we can note that the vertical illuminance for December 21st is

greater than the vertical illuminance for june 21st. this is due to the difference in the solar

altitude. As it was shown in part 1, the solar altitude for 21st June is 67.9 degrees and on

21st December is 21.05 degrees. Therefore, the lower the angle of solar altitude, the

higher the illuminance in the vertical directions. However, the horizontal illuminance for

both months will have opposite affect. Meaning that in June 21st the horizontal

illuminance will be higher than the horizontal illuminance of December 21st. this is

because the angle from the horizontal view for June will be lower than the angle view of

December.

Conclusion

Its concluded from this experiment that the orientation of the sun and the

time of the day as will as the month of the year, can affect the lighting of a building and

any ways. One-way is to increase or decrease heat gain or loss of a building. If we

oriented the windows of a building to the range of solar altitude angles between 21 to 56

(Des - Apr) degrees, the building will gain more heat from the sun during the winter

season, which can reduce the cost of heating. On the contrary, if we want to cool a

building in hot climate, we can orient the windows of the building in lower range of

angles, so that the sun will not face the building. Thus, heat gain from the sun will be

reduced which can will result in lower energy cost.

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