Operating hours befor replacement
(this will depend on the survival characteristics of the particular lamp,
usually 90% or greater, this is determined from manufacturers data (e.g. for
triphosphor lamps this would be over 12,000 hours).Group replacement should usually be
recommended at these hours as this is likely to maintain the quality of the
scheme rather than just spot replacement carried out when a lamp fails as
this is often negelcted.

Determine number
of hours before lamp replacement =

(H1)

Calculate the Total hours per
year:

(H2)

Hours/Day x
Days/Week x Weeks/Year

Number of years before
replacement will be:

H1

H2

years

Lamp Lumen Maintenance Factor (LLMF) and Lamp Survival Factor
(LSF)

LLMF

=

Determined from manufacturers data

LSF

=

Determined
from manufacturers data

(= 1.0 if * applied)

* NB if a combination of Group
Replacement and Spot Replacement is carried out so as soon as a lamp fails
inside the Group Replacement interval it is replaced immediately then LSF =
1.0.This is recommended as not only
is the quality of the scheme protected but also a higher Maintenance Factor
will be realised which is likely to mean fewer luminaires and the potential
for a commercial advantage.

NB. For a
luminaire to be classed as Direct/indirect at least 20% of the output must be
upward light.

TYPE (A+ to E):

CLEANING INTERVAL:

years

ENVIRONMENT:

C = CLEAN / N = NORMAL / D = DIRTY

For luminaire classification (A
to E) use manufacturer's data or SLL code table 3.5 and 3.6.For definitions of Clean (C), Normal (N),
or Dirty (D) see SLL code table 3.5

*NB Correction Factor CFF needed for 0% or 10% floor

CEILING:

WALLS:

FLOOR:

*

Utilisation Factor UF(F)

From manufacturer's table

UF(F)
=

if CFF is required…

UF(F)a

=

x

=

UF(F)a

=

Initial Lamp Lumens (per lamp)

From manufacturer's data

F =

lumens

TOTAL LAMP LUMENS REQUIRED

You will need to
enter UF(F) or the adjusted value (UF(F)a) if CFF is required

UF(F)

=

UF(F)a

=

Enter UF(F) or
UF(F)a value

Maintained Illuminance

x

Working Plane Area (L x W)

Utilisation Factor (UF or UF(F)a)

x

Maintenance Factor (MF)

x

x

TOTAL LAMP LUMENS
REQUIRED:

lumens

NUMBER OF LAMPS
REQUIRED = N =

TOTAL LAMP LUMENS REQUIRED

INITIAL LAMP LUMENS PER LAMP

N =

N =

lamps

Rounded up

N =

lamps

NUMBER OF LUMINAIRES REQUIRED (N2)

N2 =

NUMBER OF LAMPS

N2 =

NUMBER OF LAMPS PER LUMINAIRE

N2 =

luminaires

Rounded up

N2 =

luminaires

Spacing Requirements

N2 (

) is the number of luminaires to
provide the required design illuminance.

However
the spacing requirements also need to be satisfied.This is determined by checking against

the SHR MAX (

).To find S, complete the following.

S =

SHR MAX

x

Hm

S =

x

S =

meters

S is the
maximum distance in both the Transverse and Axial planes of the luminaire,
which is applied to the room to ensure good uniformity.To find the number of rows and columns of
luminaires in the room determine N3 and N4 by completing the following...

N3 =

LENGTH OF ROOM

S

N3 =

Rounded up

N3 =

N4 =

WIDTH OF ROOM

S

N4 =

Rounded up

N4 =

NB. N3 and N4 must always be rounded up!

The total number of
luminaires N5 to satisfy the uniformity requirements is…

N3

x

N4

x

N5 =

As both the spacing AND design
illuminance requirements must be satisfied, the number for the scheme (N6)
must be the greater of N2 or N5

N2 =

N5 =

N6 =

luminaires

...AS THIS IS THE GREATER
OF N2 AND N5

THESE MUST BE
ARRANGED AS AN ARRAY:

x

These become your Revised N3 and N4

Revised

N3 =

Revised

N4 =

Possible Arrays: N6
(

) is the total number of luminaires required for the scheme.

But also no fewer
than N3 (

) or N4 (

) across the length and
width of the room

must be selected or the scheme
will fail the uniformity requirements.Also, as you cannot have a fraction of a row or column of luminaires,
the number is quite likely to be rounded up.

Spacing of Luminaires in the Room

After rounding, the spacing for the scheme (m) will
then be….

S1 =

LENGTH OF ROOM

=

REVISED N3

round this down

S1 =

S2 =

WIDTH OF ROOM

=

REVISED N4

round this down

S2 =

For aesthetic reasons, with non
square luminaires the longest side of the luminaire is often selected to be
parallel to the length of the room, however in some circumstances the reverse
may be selected (e.g. to direct light onto a particular wall)

Modular Ceiling Systems

Modular ceiling grid is 300mm, 400mm, 500mm, 600mm,
1200mm

600mm ceiling grids are by far the most common, but
always check!

For these, N3 and N4 (which may
have been adjusted as above) must be used to check / amend the modular
spacing to ensure that they fit with the modular ceiling grid as follows…

Revised

N3 =

Revised

N4 =

S1mod =

LENGTH OF ROOM

=

REVISED N3

adjust this
for grid spacing and enter below

Before you enter
the S1mod, make sure you do not exceed the SHR MAX:

S1mod =

...manually adjusted for
grid spacing

S2mod =

WIDTH OF ROOM

=

REVISED N4

adjust this
for grid spacing and enter below

Before you enter
the S2mod, make sure you do not exceed the SHR MAX:

S2mod =

...manually adjusted for
grid spacing

E.g.
If the length of the room was 10m and 5 luminaires were to be used, spacing
would be 10 divided by 5 which is 2 meters; for a 600mm ceiling grid this
could be 1.8 or 2.4 meters ect.However, the SHR MAX must not be exceeded so a spacing check should be
carried out.

Checking for Compliance with SHR Criteria

For these calcs you will need to
enter, in the grey cell, the correct spacing values depending on whether you
have used S1 and S2 or S1mod and S2mod (if you are planning for modular
ceiling grids).

S1 =

S2=

S1mod =

S2mod=

Y =

S1 or S1mod

=

Hm

Y =

Rounded down

Z =

S2 or S2mod

=

Hm

Z =

Rounded down

Checking for Actual Illuminance of the Scheme

You will need to enter in the grey box the UF(F) or the
adjusted value (UF(F)a) if CFF is required.

UF(F)

=

UF(F)a

=

if CFF is required.

Number of Luminaires x Lamps per Luminaire x Lumens per Lamp
x (UF(F) or UF(F)a) x MF

Note: The above number of luminaires and spacings must now be
transferred to the plan drawing of the room.

Remember that the spacing is the distance between the centres of the luminaires, and that the spacing between the
last luminaire of a row and the adjacent wall (known as the end spacing) must not be more than one half of the spacing between the
luminaires in that particular direction.That is, the 'transverse end spacing' must not be more than half of the
'transverse spacing' and the 'axial end spacing' must
not be more than half of the 'axial spacing'

This may be difficult or
impossible with modular ceiling systems, here the 'best fit' must be applied.

The above method should ensure that in all cases the spacing is
within acceptable limits, in any case it is good practice to space within the
limits of the SHR MAX to reduce the likelihood of shadows.The lumen method assumes that the working
environment, including the working plane, is flat and horizontal with no
obstructions, clearly this is the exception raher than the rule.

DISCALIMER - This Lighting Design Worksheet
is based on the LIF Certificate Course Lighting Design Worksheet (JRH
20/9/2007) and it intended to be used as a guide only.The spreadsheet, and all subsequent
versions of it are provided without guarentee and are used at your own
risk.Follow me on Twitter Username MrMoaks

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