You can prepare a lighting scheme in one of three ways:
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DIY, following the steps below.
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Using your own lighting software loaded
with Illuma's photometric data.
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Using Illuma's lighting design team.
DIY lighting design
You can use the beam diagrams to produce a
simple lighting scheme. The lamp itself determines
the lighting performance of fittings that take
reflector lamps rather than the fitting. Illuma
publishes beam diagrams for these reflector
lamps based on manufacturers' data. With fittings
for other lamps, such as compact fluorescent
lamps, the lighting performance is determined
by the combined effect of the lamp and the
reflector within the fitting. Illuma publishes
photometric data, including beam diagrams.
The best way to explain how to use beam diagrams is to work through an example:
- First, measure the room; for this example,
it is assumed to be an office that is 4m long,
3m wide, 2.8m high, with a desk height of
0.8m. From these dimensions work out the distance
from the ceiling / fitting to the desktop
/ worksurface, which in this example is 2m
(i.e. ceiling height minus desk height).
- From Table 1 you can see that the required
light level for an office is 500 lux.
- Beam diagrams give the'spot diameter' (which
is the diameter of the spot or circle of light)
in metres at one, two, three and four metres
from the lamp/fitting. The spot diameter is
equivalent to the maximum distance between
fittings to provide even illumination.
In this example, the distance from the fitting
is 2m, so you need to find a lamp that will provide
500 lux or more at a distance of 2m from the
fitting. From the beam diagrams. you can see
that a 12V, 5OW, 38o beam reflector
lamp will give you the required light level,
with a spot diameter of 1.38m.
- From the 'lndex by Lamp Type', you can see
that there is a wide range of fittings that
will take this lamp. For this example, assume
that you chose a 12V Baffle Downlight (D257X)
because the lamp is set back inside the fitting,
minimising the angle from which you can see
the lamp, thereby reducing glare.
- You now need to calculate the number
of fittings that you require. To calculate
the number in each row, divide the length
of the room by the spot diameter (4 ÷ 1.38 = 2.9).
Then round up to the nearest fitting and add
one to allow for half-spacing adjacent to
the walls (2.9 > 3 + 1 = 4). Thus 4 fittings
per row are required.
To calculate the number of rows, first
divide the width of the room by the spot
diameter (3
÷ 1.38 = 2.2). Then round up to the nearest
fitting and add one to allow for half-spacing
adjacent to the walls (e.g. 2.2 > 3 + 1
= 4). Thus 4 rows of fittings are required.
So altogether you require 4 rows x 4 fittings
= 16 fittings.
- To work out the position of the fittings,
divide the length of the room by the number
of fittings (4÷ 4 = 1.0). Thus the lengthways spacing between
fittings should be 1.0m, with 0.5m between
the last fitting in the row and the wall.
Then do the same for the spacing across the
room, dividing the width of the room by the
number of fittings (3 ÷ 4 = 0.75).
Thus the widthways spacing between fittings
should be 0.75m, with 0.38m between the
last fitting in the row and the wall.
- Now draw a floor plan and mark the position
of the fittings on it using the measurements
calculated above, so that the electrical
contractor can carry out the installation.
You may have to adjust the plan to cater
for joists and other services that make
it impossible to install the downlights at
the exact points marked on the drawing. If
so, try to maintain the symmetry of the layout
and always install too many rather than
too few fittings to ensure you achieve the
minimum recommended light level.
This
example assumes that you require even lighting
over the whole room, and does rot take account
of windows or of surface reflectances of walls,
floor and ceiling. Different colours and
different materials absorb or reflect varying
amounts of light.
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You
should only use this method to work out the
simplest of lighting schemes. If you have
pictures on the wall or other items of interest
to highlight, you will need to make sure that
you have enough fittings to cater for these
additional requirements and may need to add a
further row of fittings. It is always better to have too many fittings and then use dimmers to change light levels, than it is to have too few fittings. You need to be particularly careful when planning lighting designs for
downlights. because adding downlights to a regular layout after the installation has been finished is always expensive and disruptive, and it is almost impossible to do without compromising the appearance of the installation.
Note: Interim values other than those shown in the beam diagrams can be easily calculated using the following formula:
lux at any given distance in metres = lux at one metre
÷ distance squared
For example, the lux at 2.5 metres equals lux at one metre divided by
2.52.
The diameter in mattes of the spot or circle of light (at the circumference of which lux values are half that at the centre) can be calculated thus:
diameter in metres = tan
y°÷ height
where y is half the beam angle of the lamp.
To assist with the preparation of simple lighting schemes, Illuma has produced a handy, credit-card sized pocket guide, the
LuxPlan© Ready
Reckoner, which covers five commonly-used reflector lamps, and five of Illuma's most popular compact-fluorescent
downlights.
Or,
create your own Lighting Scheme using the
Relux
Lighting Design Software. You can prepare
your own computer generated lighting schemes.
Please
call us on 0845 6060414 for
your free CD-Rom.
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