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    Lighting Design Calculator




    ROOM LOCATION:
    FUNCTION:
    ENVIRONMENT:
    C = CLEAN / N = NORMAL / D = DIRTY
    MAINTAINED ILLUMINANCE: lux
    LENGTH (L): meters
    WIDTH (W): meters
    HEIGHT (H): meters
    SUSPENSION (H1): meters
    WORKING PLANE HEIGHT (H2): meters
    MOUNTING HEIGHT (Hm) meters
    (Hm) = H - (H2) - (H1)
    ROOM INDEX K = L x W K =
    (L + W) x Hm
    K =
    LUMINAIRE SELECTED:
    MANUFACTURER:
    CAT No / REF:
    DESCRIPTION:
    TYPE of LAMP:
    INDIVIDUAL LAMP WATTAGE: watts
    NUMBER of LAMPS:
    TOTAL LAMP WATTS: watts
    LUMINAIRE LENGTH: mm
    SHR MAX:
    SHR MAX TR:
    SHR NOM:
    LAMP TYPE:
    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.
    Luminaire Classification
    Direct, Direct / Indirect, Indirect:
    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
    LMF =
    Room Surface Maintenance Factor (RSMF) - SLL Code Table 3.7
    ENVIRONMENT:
    C = CLEAN / N = NORMAL / D = DIRTY
    CLEANING INTERVAL: years
    ROOM INDEX K =
    Direct, Direct / Indirect, Indirect:
    RSMF =
    Maintenance Factor (MF)
    MF = LLMF x LSF x LMF x RSMF
    MF = x x x
    MF =
    Reflectances of Room
    *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
    Working plane Area (L x W)
    x x x x
    =
    ILLUMINANCE = lux
    TESTS
    Complies?
    Yes / No
    SHR for the length of the room (Y) must be less than SHR MAX
    SHR for the width of the room (Z) must be less than SHR MAX
    SHR if mounted end to end SHR must be less than SHR MAX TR (not typical)
    Actual illuminance should be within 10% of the design value
    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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