artificial lighting practical

7/31/2019 Artificial Lighting Practical

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ARTIFICIAL LIGHTING PRACTICALLEARNING OBJECTIVES:

UNDERSTAND THE CONCEPT OF EFFICACY UNDERSTAND INVERSE SQUARE LAW AND ITS IMPLICATIONS FOR ARTIFICIAL LIGHTING UNDERSTAND THE DIFFERENT TECHNOLOGIES THAT CAN PROVIDE ARTIFICIAL LIGHTING, THEIR

BENEFITS, CHARACTERISTICS AND LIMITATIONS. UNDERSTAND THE CONCEPT OF COLOUR RENDITION UNDERSTAND THE CONCEPT OF COLOUR TEMPERATURE UNDERSTAND HOW DIFFERENT LIGHTING TECHNOLOGIES GENERATE WHITE LIGHT

INTRODUCTION

From open fires, to earthenware pots full of oil with wicks through to the manufacture of

candles, gas lighting and more latterly electrical lighting; first arc lighting, then the

incandescent lamp tomorrow the L.E.D.? The human race has used all manner of

technologies to provide artificial illumination, and lengthen the working day.

Artificial lighting is any form of lighting which is not sunlight. Artificial lighting adds utility to

buildings, providing both aesthetic and practical improvements to architecture. Artificial

lighting represents a major component of building energy consumption and so we should

be aware of the different types of artificial lighting technologies. This practical workshop

aims to provide an introduction to different lighting technologies, their characteristics and

energy performance.

Artificial lighting also has energy implications beyond the energy consumed by the lights

themselves. The energy dissipated by lights is a contributing factor to space heat gain andspace cooling load in many commercial buildings. (Chantrasrisalai & Fisher) through

quantitative measurement of the heat and light produced by different technologies

INVESTIGATING INVERSE SQUARE LAW

YOU WILL NEED :

Optics Bench & Brackets To Support Components Bulb, Battery & Connecting Wire Sheet of Black Card Sheet of White Card Photometer

EXPERIMENTAL METHOD

The following needs to be carried out in a room that can be made dark. We are

going to experimentally evaluate the diagram below; which gives us a representation

of Inverse Square Law.

Inverse square law states that the light that can be measured at a given distance

from a bulb, is inversely proportional to the square of the distance from the source

of the luminous flux.


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First, set up the bulb at one end of the optics stand. Make the room dark, and

connect the bulb to the battery to illuminate it. We are going to measure the light

level at a variety of different distances from the bulb.

The photosensor of the photometer is unidirectional which means that it only

measures light hitting it from the distance it is facing. Therefore position it with the

sensor facing towards the bulb, and the soldered connections to the rear facing

away.

The photometer can be adjusted to operate in different light levels. The range

button can be used to adjust the sensitivity of the photometer. Move the sensor

from the photometer along the length of the optics stand, allowing a fair distance

from the bulb; and use the range control, to find a position and setting at which the

meter on the photometer reads 1. Measure the distance between the centre of the

bulb and the Photometer sensor using the scale on the optics bench. This will be

our 3xD position. Divide this measurement by 3 and using the scale on the bench,

make measurements at D and 2xD

Look at the relationship between the measurements at D, 2xD and 3xD.

The next stage of the experiment, is to take the black piece of card, and make a

shadow mask with a 1 centimetre square aperture in the middle of the card.

Position this aperture at the D measurement on the optics bench. Now hold the

white sheet of card at the 2xD and 3xD positions; and at each time look at the light

which is cast on the sheet, draw a line to mark the boundary between light and

darkness and measure the area of the light squares. (Note there is actually a bit of a

cheat here, in that the wavefront will spread spherically from a point source but

we are measuring a flat plane, just to keep the measurements simple!).

A

4A

9A

Illuminance (lux) LL

4

L

9


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INVESTIGATING L IGHT & COLOUR TEMPERATURE

YOU W ILL NEED

Spectrascopes Range of different artificial light sources

EXPERIMENTAL METHOD

We are going to use a spectroscope to evaluate the colour components of a range

of different light sources.

We know that white light is composed of a spectrum of different colours an

incandescent lamp produces light across the spectrum, as the white hot filament

releases thermal energy in the form of photons, when connected to a source of

energy. Conversely, other light sources, for example fluorescent lamps, produce

signatures in the spectra a purple line can be seen; this is the purple light

emitted by the mercury vapour as it is excited; however, this purple light then needsto hit phosphors; which vary depending on the type of lamp. These phosphors in

turn emit light, but rather than the uniform spectrum we observe with incandescent

lamps; we see a number of well defined colour bands often red, green and blue in

triphosphor lamps, with very little in-between.

By looking at the spectra emitted by different light sources, we can understand the

mechanisms used by different technologies to produce light. Furthermore, we can

also make judgements about how well these light sources are able to render othercolours.

WHAT IS A SPECTROSCOPE?

A spectroscope in essence consists of a slit through which light can pass and a

diffraction grating or prism. The diffraction grating or prism splits white light into its

constituent components. We are going to use a crude and simple spectroscope to

make a comparative analysis of a handful of different light sources. The spectroscope

will take the form of a tube which we look through and point towards the light.

Spectrascope

Light Source

Light SourceDifferent light sources producedifferent characteristic spectra.

There are clues about colour

rendition and how the light is

produced from these spectra.


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INVESTIGATING LAMP EFFICACY

YOU W ILL NEED :

Range of light bulbs

Mains lead with appropriate electrical fittings for bulbs Insulated Box With Reflective Interior Thermometer Photometer

EXPERIMENTAL METHOD

We will be appraising the efficacy of a range of different bulbs; We will be measuring

the energy that the bulbs consume using an energy meter; using a light meter, we

can then appraise the amount of light the bulb produces. Furthermore we can then

monitor the temperature inside the box and compare it to the outside temperature

(and for really advanced analyses; the box is of known construction and surfacearea). Using these measurements, we can look at how much of the electrical energy

is transformed into useful energy in the form of light emitted; and how much iswasted as heat.

LEVELS OF ANALYSIS

Using this simple apparatus we can make a number of different levels of analysis.

The simplest is just a comparison between different bulbs this could takethe form of a ranking this bulb experimentally proved to be more

efficient than this one.

A more sophisticated analysis might look at the heat loss through the box calculate or simulate this to work out how much heat the bulb is emitting

and construct a Sankey diagram, or similar to show how the electricalenergy is being transformed into heat and light.

Heat(Measured Using Thermometer)

Electricity

(Measured Using Energy Meter)

Light(Measured Using Photometer)

The inside of the box is

highly reflective to

ensure light from all

directions is reflected

towards the sensor.

The box is insulated

and of known

construction so that

the heat loss through

the walls can be

calculated.

The flow of electrons to the bulbs

will be measured using a plug-in

energy meter. This meter will give

an indication of the power (the

rate of doing work) and the

energy (the total amount of

work done).

Luminous Efficacy =Light (Lumens)

Power (Watts)

artificial lighting practical

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