Lux Contour Office Analysis Tutorial

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bentleykf
Posts: 85
Joined: Wed Jun 03, 2009 11:09 am

Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 8:25 am

Introduction
I'm currently using LightUp's Lux Contour feature to test good(read as efficient) office lighting design, so I thought I should fill in some info on this process using LightUp. First I'll go through the basic methods of choosing appropriate luminaires given the data available for the room intended for lighting, then I'll go onto specific lighting evaluation using LightUp's Lux Contour feature. Sorry if this bores the pants off some people, but it can be helpful to know for the early stages of modelling your building.

For an analysis of the feature, I've used a testing room similar to the Classroom in LightUp's gallery. The room has no windows and is totally reliant on direct, artificial sources of lighting. The grid layout shown is 1m x 1m for every thick black line.

Brief
  • Room Shape: The room has a length of 13000mm, a width of 9000mm and a height of 2700mm.
  • Working Plane: 700mm above FFL (Finished Floor Level) - typical.
  • Mounting Height: 2400mm above FFL - typical.
  • Lamp Type: T5 flourescent lamp - typical.
lightup_office-space-01.jpg
Office dimensions and set out.
lightup_office-space-01.jpg (140.44 KiB) Viewed 20420 times
Interpretting Manufacturer's Data
As you probably know manufacturers provide data on the performance of their luminaires on their website. If the manufacturer is considerate enough to provide the appropriate data we can determine the effectiveness of certain luminaire types based on the proportions of our room, but what we first need to do is determine a Room Index (K) value.

Room Index (K) value
A Room Index value is a number that describes the ratios of the rooms length, width and height. These dimensions directly effect the performance of a specific luminaire, so determining your Room Index value is very important when considering luminaires for your room. The Room Index (K) value is determined by this formula;

K = [L x W] / [[L + W] x Hm]

where:
  • K = Room Index Value
  • L = Room Length in Metres
  • W = Room Width in Metres
  • Hm = Distance between Mounting Height of luminaire and the Working Plane in Metres
NOTE #1: As a simple rule of thumb, a space with a K value greater than 3 is a very efficient space to light, and a space with a K value less than three is considerably less efficient to light.

So using this equation for the office space we get a value of 3.13 ([13x9]/[[13+9]x1.7]=3.128...), which is pretty good for office lighting. The next step is to choose an appropriate luminaire to light our room, and determine how many luminaires we will need. This can be done using the Utilisation Factor (F) for the luminaire to give a rough estimate of the effectiveness of the luminaire to light the working place, and the Lumen Method Caculation to determine how many luminaires we will need to light the workplane to a specific lux value.

Utilisation Factor (UF)
http://www.ndlight.com.au/lighting_calculations.htm wrote:This is a value between 0 and 1 that represents the percentage of total lamp lumens in the room that fall on the work plane. It takes into account the room reflectances, room shape, polar distribution and light output ratio of the fitting.
Considerate manufacturers provide this data so you can appropriately assess their products efficiency in your room. So from the Thorn Lighting US Indoor Catalogues CalcExpress feature for specific Luminaires (CalcExpress calculates your room index from the values you input for length, width, height) we can get a utilisation factor (UF) of 78% (or 0.78) for the Luminaire QUATTRO M 2x14w T16 HF L840 in the office space. This means that 78% of the light produced by the lamp will be useful on the workplane, and 22% will be lighting some other surfaces, which is pretty good imo.
lightup_thorn-calcexpress-01.jpg
Thorn's CalcExpress data and the Utilisation Factor
lightup_thorn-calcexpress-01.jpg (112.96 KiB) Viewed 20421 times
This utilisation factor is also determined by the reflectances of your rooms walls, ceiling and floor (noted sometimes as W, C and F respectively). Typical reflectance values are 0.7 (70%) for the ceiling, 0.5 (50%) for the walls and 0.2 (20%) for the floor. I would suggest hunting down the reflectance values of highly reflective materials from the manufacturers website if you intend to use them, but the typical values are often the best to go with if you haven't yet decided on materials.

Interpretting Manufacturer's Data
There are a few calculations that you can make using data direct from the manufacturer which help in designing your luminaire layout on the ceiling grid, but the first calculation you should consider is the Lumen Method Calculation.

Lumen Method Calculation
The Lumen Method Calculation is an equation used to determine how many luminaires are required. It functions by first deciding on an appropriate level of illumination required for the working plane, and then using data obtained from the luminaire manufacturer, estimates an appropriate number of luminaires required to achieve this level of illumination. The equation is as follows;
http://www.ndlight.com.au/lighting_calculations.htm wrote:N = [E x A] / [[F x UF x LLF]

where:
  • N = Number of Fittings
  • E = Lux Level Required on Working Plane (Maintenance Illuminance)
  • A = Area of Room (L x W)
  • F = Total Flux (Lumens) from all the Lamps in one Fitting
  • UF = Utilisation Factor from the Table for the Fitting to be Used
  • LLF = Light Loss Factor. This takes account of the depreciation over time of lamp output and dirt accumulation on the fitting and walls of the building.
So we've already worked out our Ultilisation Factor (UF) from calculating our room index (K) and obtaining the appropriate UF for our luminaire relative to our room index from the manufacturer. What is required is the Maintenance Illuminance (E), the Total Flux in Lumens (F), and the Light Loss Factor (LLF), so lets talk a bit about those;

Maintenance Illuminance (E)
The first is the illumination required for the working plane. A good starting point to defining this value is to check with your local or regional (state/country) building codes for recommended maintenance illuminances for various types of tasks. The Australian Standards set out maintenance illuminance values similar to this;
  • 40 lux: Movement and Orientation, areas where visual tasks are rare
  • 80 lux: Rough Intermittent, areas where visual tasks involve movement, orientation and coarse detail
  • 160 lux: Simple workplace tasks, continuously occupied area where tasks include occasional reading for short periods
  • 240 lux: Ordinary/Easy workplace tasks, continuously occupied area where tasks have high contrast or large detail
  • 320-400 lux: Moderately Difficult, continuously occupied area where tasks are moderate and have low contrasts
  • 600 lux: Difficult, continuously occupied area where tasks have small detail
  • 800 lux: Very Difficult, very small detail tasks
  • 1200 lux: Extremely Difficult
  • etc.
So for a typical office space, the illumination required for the working plane is between 320 and 400 lux.

Also I should mention that some Green Accreditation orginisations such as Green Star here in Australia assess light levels provided by luminaires on the working plane. In Green Star - Office Design v3:
Green Star - Office Design v3 wrote:One point is awarded where:
The office lighting design has a maintained illuminance level of no more than 400 lux for 95% of the Class 5 Commercial Office NLA [Net Lettable Area] as measured at the working plane (720mm AFFL).
So for our office space, we'll be aiming for an average of 320 lux of illumination on the working plane, and i'll talk a little about achieving a uniformly lit working plane a little later.

Total Flux in lumens (F) of all Lamps per Fitting
Rather than bore you to death with further calculations and definitions, the total Flux in lumens (F) for a luminaire is fancy way of saying the value for the initial lamp lumens multiplied by the number of lamps in a luminaire. For instance, our previous example from the Thorn Lighting website, the 'QUATTRO M 2x14w T16 HF L840' uses two T16/14W lamps ('2x14w T16'). Each of these lamps outputs 1200 initial lamp lumens, so the Total Flux in lumens (F) for the luminaire is 2400 lumens. This represents the initial output in lumens of the luminaire.Some manufacturers provide this data, some don't. For the manufacturers that don't publish the flux in lumens, try tracking down lamp manufacturers that make the lamp that your luminaire uses. For our luminaire, this would be a 14 watt T16(or T5) flourescent lamp. An example is from the osram site;
lightup_osram-technical-data-01.jpg
Osram technical data for a 14W T5 High Efficiency lamp
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Now its quite easy to assume that this value 2400 lumens for each luminaire won't be achieved for the entire life-span of the luminaire, so the Lumen Method Calculation features the Light Loss Factor (LLF) to ensure that at the time when this luminaire outputs the lowest amount of light (just before cleaning/replacement of the lamps), the required Maintenance Illuminance level of the working plane is still achieved.

Light Loss Factor (LLF)
To put it simply, as the hours of use a particular lamp increases, its lumen output decreases. This is due to the accumulation of dirt and the general reduction in efficiency and functionality of the lamp. So how do you determine your light loss factor? Well as a rule of thumb for dirt accumulation, the following factors can be used;
http://www.ndlight.com.au/lighting_calculations.htm wrote:Air Conditioned Office: 0.8
Clean Industrial: 0.7
Dirty Industrial: 0.6
So our Light Loss Factor (LLF) for our office is 0.8.

Calculating the Amount of Luminaires Required
So with the above information we can get an approximate estimate of how many luminaires we should need to light our working plane to the appropriate maintenance illuminance;

N = [E x A] / [[F x UF x LLF]
  • N = [320lux x 117msq] / [2400 lumens x 78% x 0.8]
  • N = 25 luminaires
Obviously this equation doesn't always put out rounded integers, so in situations where you get something like 25.25 luminaires you should always round up so you get a value just above what you require. So how do you determine the grid layout for these 25 odd luminaires?

Determining the Grid Layout
There are two simple equations for determining the grid layout of your luminaires. They are;

NL = Sq Root[N x [L/W]]
NW = Sq Root[N x [W/L]]

where:
  • NL = Number of Fittings required for the length of the room
  • NW = Number of Fittings required for the width of the room
  • N = Total Number of Fittings
  • L = Length of Room
  • W = Width of Room
So from these equations we get an NL of 6.1 (Sq Root[25 x [13/9]]) and an NW of 4.16. Obviously we can't have 0.16 or 0.1 of a luminaire, so round these numbers to the closest integer (6 and 4). When rounding these numbers also be cautious of the total number of luminaires, with 6 and 4 we get 24 total luminaires, which is one off of the 25 luminaires determined by the Lumen Method Calculation. You'll also notice that the longer dimension (the length in this example) has more luminaires. This is just because one dimension is longer than the other. These equations give a luminaire to luminaire spacing for both dimensions that are as close square as possible. What determines the luminaires orientation (ie. Parallel to the width dimension or parallel to the length dimension) is the luminaires distribution of light, but i'll talk more about this in the revision section.
Last edited by bentleykf on Sun Jul 05, 2009 9:07 am, edited 1 time in total.

bentleykf
Posts: 85
Joined: Wed Jun 03, 2009 11:09 am

Re: Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 8:39 am

Modeling in Sketchup/Lightup
So from this data we can model our lighting grid in SketchUp and then (after applying IES files) render in LightUp. To achieve the best spacing for your grid, your luminaires should have a distance from their centre to an adjacent wall of: half the distance from the luminaires centre to centre value. There is a method to do this with ease in sketchup (see note #2 below before doing this);
  1. Position a LightUp PointLightSource to the intersection of one top corner of your room.
  2. Conditional: Position the corner of a small box (or a 3d model of your light) on the same top corner of your room.
  3. Conditional: Select both your PointLightSource and your small box and right-click and make them a component. (steps 2 & 3 make it easier for you to [later] modify all your PointLightSources in your grid easier)
  4. Then copy the PointLightSource to the opposite top corner of your room along the width dimension.
  5. Then divide the copy command by double the NW result (in this case 8 for our NW value of 4, you can divide by typing the number to divide the copy command by, followed by a forward slash, and then hit enter. You must do this directly after the copy command)
  6. Then delete the odd instances of your copy command (starting with your original light source, delete every second copy of the light source)
You can do the same along the length dimension, but this time select all the copys of the PointLightSource that result from following these steps for the width dimension and make them into a group. Then copy from one top corner of your room to the opposite top corner along the length dimension and divide.

NOTE #2: By default, LightUp's PointLightSource components are set to automatically face the camera, like in the render below. If you're intending to use IES luminaires that aren't axially symmetric (such as most rectangular flourescent office luminaires) you should turn this off. To do this go into components->In Model and right-click LightUp's PointLightSource component, select properties and un-tick the checkbox next to 'Always Face Camera'. Next drag in your PointLightSource to your model and orient. Use LightUp's query tool to show the photometric web to determine if its orientation is correct.

So here's the resulting grid layout with spacings and the small boxes hidden (of course we have to move our PointLightSources down to our Mounting Height of 2.4 metres after this.
lightup_office-space-02.jpg
Ideal lighting grid dimensions for our office space
lightup_office-space-02.jpg (123.04 KiB) Viewed 20420 times
After you've modelled your lighting grid in SketchUp, first you need to apply IES files to all your lights before producing a lux contour render in lightup. For this you'll need the IES file from the manufacturer, and they're often hiding in obscure places. On Thorn's US website you can access them through their electronic catalogue (Products->Electronic Catalogue), then navigate your way to the specific product page and click the 'Downloads' tab at the top of the products page. The IES file is normally under the 'Design Data' section of the downloads page. Now once the file has downloaded you'll need to add the file to an existing point light. Adam has done a quick video tutorial on loading in the IES files to your point lights so please take a look at it if you haven't already. I'd recommend having your luminaire model/point lights in your array as a component together, then you won't need to go to each point light to load in the IES file. Just create a box and make the box and PointLightSource a component then hide the box if you don't have a luminaire model.

So for all your hard work here's the LightUp Lux Contour render of your lighting grid (with a little post-processing to show the PointLightSources);
lightup_office-space-03.jpg
LightUp Lux Contour render of our lighting grid with 2x14W QUATTRO M luminaires
lightup_office-space-03.jpg (176.96 KiB) Viewed 20420 times
As you can see there's a fairly even distribution of light over the working plane, though as shown theres a variation of 60 lux (which is significant) in areas that would be commonly used by the occupants. This is a little bit inconsistent with our Lumen Method Calculation, which estimated the number of luminaires for a minimum of 320 lux on the workplane. So what are the ways in which you can revise this design?

NOTE #3: LightUp's accuracy in determining lux levels in lux contours is directly reliant on the resolution you set in the preferences pane. For more accurate lux readings, set your resolution higher and in your models units. In the previous render the resolution was set to 1cm (which is quite insane for complex models, but ideal for a simple lux level analysis). Be wary at first as your render time will increase significantly if you increase the resolution.

Revising the Lighting Design: Less Luminaires
25 luminaires seems like a lot, and it is quite a large amount for a space thats only 117 metres squared. Even though our luminaire is quite efficient at lighting the working plane (78%), it isn't supplying enough light to the working plane. So what can we do in this situation?

Reducing the amount of Luminaires Required
Ideally, we would choose a similar luminaire that was more efficient at lighting the working plane, as this would reduce the number of luminaires required, and thus reduce the amount of power used in lighting. But normally this isn't possible, as you may have wisely chosen the most efficient luminaire to light your working plane in the first place. So what other options are there?

Bar reducing your minimum maintenance illuminance level (which I wouldn't recommend) and reducing/changing the width and length of the space (modifying A in the Lumen Method Calculation, and ideally giving you a better Room Index (K) which modifies the UF value in the Lumen Method Calculation), you can change the lamps to ones that produce more light. So lets choose another luminaire from the 'Quattro M' line and run the calculation again.

The 'QUATTROM 2x28w T16 HFD L840' is the highest lumen producing luminaire from the 'Quattro M' line. Its total flux is 5200 lumens (2x2600 lumens), and its Utilisation Factor is 78% (the same as the previous model, yet we should recalculate the UF everytime we change the luminaire/lamp). So for the Lumen Method Calculation we get;
  • N = [320lux x 117msq] / [5200 lumens x 78% x 0.8]
  • N = 11.54 luminaires (12 luminaires)
Here's the resulting LightUp render;
lightup_office-space-04.jpg
LightUp Lux Contour render of of our lighting grid with 2x28W QUATTRO M luminaires
lightup_office-space-04.jpg (162.73 KiB) Viewed 20420 times
You'll notice in the render that reducing the amount of luminaires and increasing their output has severely decreased the uniformity of light on the workplane. The illumination on the workplane ranges a full 700 lux, and considering that we were designing for a minimum of 320 lux, the Lumen Method Calculation isn't the ideal method for detemining a uniformly lit working plane. Its obvious that there are more factors at play here than that are considered in the Lumen Method Calculation, so lets talk more on those.

NOTE #4: I should also mention that reducing the number of luminaires in a room and increasing their light output increases the chances of glare occurring in the workplace. Certain green certification methods might assess the glare created in the workplace, so be careful. As a general rule, more luminaires with less output means less chance of glare.
Last edited by bentleykf on Mon Jul 13, 2009 2:54 pm, edited 2 times in total.

bentleykf
Posts: 85
Joined: Wed Jun 03, 2009 11:09 am

Re: Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 8:57 am

Revising the Lighting Design: Uniformity

As I've said, the Lumen Method Calculation has its drawbacks, but I should say this: the Lumen Method Calculation's accuracy in determining uniformity is initially dependant on an appropriate luminous flux from a lamp relative to the desired illumination required. In other words, the higher the luminous flux from a lamp and the lower the desired illumination required, the less accurate this calculation is. I should also say that the Lumen Method Calculation is particularly blind to the distribution of lux levels. The utilisation factor used in the calculation merely estimates the proportion of light hitting the workplane, it doesn't consider the distribution of this light across this workplane. You can see this uneven distribution of light in the previous LightUp render. Some problems with non-uniform light distribution are pretty apparent, and some are a little more abstract;
  • there is inefficiency as you may only require 320 lux for ambient maintenance light, and any higher light levels in your design might be provided by desk lamps/luminaires that the inhabitant switches on and off when required
  • higher light levels may produce glare from reflective surfaces on your working plane which can be pretty distractive, hazardous and even debilitating
  • your green certification organisation may require that light on the working plane should not exceed a certain lux level
  • your green certification organisation may require a uniformly lit proportion of the working plane (ie. 80% of the working plane should not exceed the designed illumination level)
So lets go back to the drawing board and try to work out a better solution.

First we'll need a measurement from the luminaire manufacturer that assesses the uniformity of light created by the luminaire. For this we're going to use the Spacing Height Ratio (SHR).

Spacing Height Ratio (SHR)
The spacing height ratio determines the maximum spacing between each luminaire to achieve a relatively uniform lighting condition on the working plane by using the distance between the luminaire mounting height and the working plane. The spacing height ratio value comes in different forms, those being: SHR nom, SHR max, SHR tansverse, and SHR axial. I should define each;
  • SHR nom: This is the rounded (to 0.25 increments) spacing ratio between each luminaire that achieves an acceptable uniform lighting condition. It is the nearest multiple of 0.25 that is below SHR max.
  • SHR max: This is the maximum spacing ratio between each luminaire which achieves an acceptable uniform lighting condition.
  • SHR trans: This value defines the spacing ratio for a linear luminaire, it is the ratio between: 'the distance of its mounting height above the working plane' and 'the distance between the centres of each luminaire perpendicular to its axis (ie. perpendicular to the direction of the lamp)' This is given because the light distribution along the transverse axis differs from the light distribution along the axial axis.
  • SHR axial: This value defines the spacing ratio for a linear luminaire, it is the ratio between: 'the distance of its mounting height above the working plane' and 'the distance between the centres of each luminaire along its axis (ie. in the direction of the lamp)' As shorthand, it is often referred to as SHR max when SHR trans is used.
A uniform lighting condition defined by the SHR max, trans and axial values represents a difference in average illuminance of no less than 30% of the maximum average illuminance. Considering that for our office space we want a minimum illuminance value of 320 lux, using together the Lumen Method Calculation and the luminaires SHR values, we can achieve a workplane that has a maximum lux level of roughly 457 lux. This is a bit above our maximum design lux level of 400 lux, so what we need is luminaires with particularly high SHR values, and a Total Flux of below 5000 lumens (so we can have more luminaires without significantly increasing the minimum illunumance on the workplane).

NOTE #5: From our first LightUp render you can see that our maximum is 370 lux, and our minimum is 310 lux. From this render interpret that the distance between our luminaires is considerably less than the luminaires SHR value, as the variation in light levels is less than 30%. LightUp's Lux Contours is a very effective way of assessing the distribution of light from a specific luminaire, however, understanding the SHR value can save you a considerable amount of time when assessing the manufacturers data before modeling your luminaire grid in LightUp.

NOTE #6: Thorn provide SHR's in their product brochures with their photometric data, but not on their product page through their website. Go to Resources->Download Product Brochures to access them. Most luminaires aren't available this way however. If you need SHR values I'd suggest contacting the manufacturer directly, as they are often in printed media, rather than freely available on the web. If anyone has any other methods of obtaining SHR values please let me know.

So lets choose a luminaire that uses a better parabolic diffuser (generally speaking, parabolic diffusers have a better distribution of light). We'll use a different manufacturer, a luminaire from the H. E. Williams catalog should suit. The 'U4 2x4 2 LAMP' with 4" parabolic louvre is ideal.
lightup_hewilliams-data-01.jpg
H.E. Williams technical data for a U4 2x4 2 LAMP with 4" parabolic louvre
lightup_hewilliams-data-01.jpg (101.05 KiB) Viewed 20420 times
You'll notice, however, something unusual about the data on this product. Instead of a Utilisation Factor we have something called 'zonal cavity coefficients', instead of a Room Index we have an RCR (Room Cavity Index), and instead of a Spacing Height Ratio we have Spacing criteria. Two of these are simple to explain, and the other not so simple. Zonal Cavity Coefficients are equivalent to the Utilisation factor, so you can use it in place of the Utilisation factor. The Spacing Criteria is the equivalent of a Spacing Height Ratio (SHR), you can use it exactly how you would use a SHR. The RCR is not so easy to explain, so lets talk about this;

Room Cavity Index (RCR)
This Index differs from the Room Index (K) in that it uses the equation RCR = 5H [L+W] / L x W, (or, alternately, RCR = (2.5) Total Wall Area / Floor Area) where H = Height, L = Length and W = Width of the room. RCR values range from 0-10. Rooms with a lower RCR value are easier (more efficient) to light, which is unlike the room index value, where rooms with a higher Room Index value are easier (more efficient) to light. Generally speaking, a room with an RCR value below 3 are quite easy to light, and a room with an RCR value above 3 are considerably harder to light.

So using this equation we get an RCR value of 2.26, which again is quite good. This gives us a Utilization Factor for our luminaire of roughly 70%. Our SHR trans is 1.9 (Across value for Spacing Criteria), our SHR axial value is 1.2 (Along value for Spacing Criteria), and our luminaire can use 2 T5 14W lamps (2400 lumens of initial output). So lets do the calculations for this luminaire;
  • N = [320lux x 117msq] / [2400 lumens x 70% x 0.8]
  • N = 27.85 (28 luminaires)
So we're using 4 more luminaires than in our first example, which is roughly a 56W increase in power. Lets determine our grid, however this time we're also going to assess our grid spacings and determine an appropriate orientation for this linear luminaire before modeling it in Sketchup/LightUp. Using our grid layout calculation we get;
  • NL = Sq Root[28 x [13/9]]
  • NL = 6.36
  • Therefore: NL Spacing = 2.044m (13/6.36)
  • NW = Sq Root[28 x [9/13]]
  • NW = 4.40
  • Therefore: NW Spacing = 2.045m (9/4.40)
As you've noticed, the equations to determine grid layout attempt to evenly distribute the luminaire positions in equal distances in both directions. But given our SHR trans is 1.9, and our SHR axial is 1.2, and our mounting height is 1.7, our luminaires should be spaced no more than 2.040m by 3.230m, so we need to modify our grid to get one dimensions spacing a little under 2.040m, and the other dimensions spacing a little under 3.230m. To achieve a rough total of 28 luminaires there are really only two ideal options and one ok option;
  • Grid Dimensions: 7 by 4
  • Therefore: Grid Spacing = 1.860m by 2.250m
  • Grid Dimensions: 14 by 2
  • Therefore: Grid Spacing = 0.929m by 4.500m
  • Grid Dimensions: 9 by 3
  • Therefore: Grid Spacing = 1.444m by 3.000m
The grid layouts of 7 by 4 and 9 by 3 come the closest to our maximum spacings of 2.040m by 3.230m determined by the SHR values, so lets model up both in Sketchup and LightUp to determine the best solution (make sure you follow Note #2 as its quite important with linear luminaires and LightUp). You'll also notice from the results of these grid spacings that the axial dimension of the luminaire is best oriented parallel to the length of our room, as if it were oriented along the width dimension, the grid spacings would exceed the SHR axial proportion of 1.2.

NOTE #7: The IES files on the H.E. Williams website are for luminaires with specific lamps. They don't seem to provide IES files for the whole range of lamps that can work in their luminaires, so some editing of the IES file is required. I'll talk a little bit about how to do this in the Appendix.
lightup_office-space-05.jpg
LightUp results for our H.E. Williams U4 2x4 2 LAMP luminaire with a 4" parabolic louvre and 2x14W lamps. On the left is the 7 by 4 grid, on the right the 9 by 3 grid.
lightup_office-space-05.jpg (133.29 KiB) Viewed 20419 times
On the left is the render for a 7 by 4 grid, and on the right is a render for a 9 by 3 grid. You can see in both LightUp renders that the light distribution is very uniform. You'll also notice that the maximum illumination is occuring in between the luminaires, rather than directly underneath them. What is obviously different between the two is the axial distribution between the two (which can be easily seen by looking at the distribution of illumination in the far wall. In the 9 by 3 grid, the distribution is incredibly even, whilst in the 7 by 4 grid there is some uneven-ness. You can also see the variation in light distribution in the transverse direction on the side walls, though given light readings from LightUp's light meter query tool show not much difference in the variation of light on the workplane in this direction.

Its quite clear that both grid patterns effectively distribute light evenly over the workplane, but whats also apparent is the levels of light are significantly higher than our design intent of 320 lux, so as a final addenum, lets consider some options to reduce the lumen output of these luminaires.

Reducing Lumen Output
It seems quite logical that from the last render that we're slightly over-lighting the workplane, and wasting energy by doing so, so what options are available to reduce the lumen output? Well the first one is quite obvious, that's choosing a new, lower wattage, lower luminous flux lamp, but in our model we're using the minimum 14W 1200 lumen lamps. Instead what we'll do is use 1 lamp per luminaire rather than two, and use a slightly higher wattage lamp. In comparison, here's our current energy usage;
  • 14Wx2x28 = 784W
  • 784W/117m sq = 6.7 watts per square metre.
Our lowest reading from the previous render in usable space was 390 lux, and we require a design lighting of around 320 lux, which is effectively an 18% reduction from what we have currently. We use a total of 2400 lumens per luminaire, yet to achieve the minimum of 320 lux we should be outputting around 1900 lumens per luminaire. A single, energy efficient 21W T5 flourescent lamp achieves this, so lets modify the previous 9 by 3 grid so that each luminaire outputs 1900 lumens. Here's the LightUp render;
lightup_office-space-06.jpg
LightUp results for our H.E. Williams U4 2x4 2 LAMP with a 4" parabolic louvre and 1x21W High Efficiency lamp.
lightup_office-space-06.jpg (156.5 KiB) Viewed 20419 times
As you can see, what results is a very even distribution of light with not much variation in illumination on the workplane. Our average illuminance doesn't vary much from 320 lux except at the very edges of our workplane, and our energy used in lighting the workplane has significantly reduced (even when compared to our very first luminaire grid design);
  • 21Wx28 = 588W
  • 588W/117m sq = 5.03 watts per square metre.
Last edited by bentleykf on Sun Jul 19, 2009 2:19 am, edited 2 times in total.

bentleykf
Posts: 85
Joined: Wed Jun 03, 2009 11:09 am

Re: Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 9:05 am

Appendices
If all this information wasn't enough there's a few conditional things I should talk about before you get a little frustrated with IES files and obscure manufacturer data. As you probably know IES files aren't supplied by all manufacturers, and although some manufacturers provide IES files for each product, they vary in their coverage of of certain custom options and variations in lamp choice.

Appendix A: Modifying IES Files
Currently LightUp doesn't provide an option to modify IES files, and quite wisely so. In Adam's own words:
AdamB wrote:...that runs totally against what IES files represent. They are a physical measurement of the luminaire output: if you changed this - rather than choose a different luminaire - you'd be invalidating that measurement...
So be wary of the following procedure, as modifying the IES file to reduce the luminous flux output to suit your lamp choice is intended as an approximation of the photometric data, and not an accurate physical measurement.

IES files are ASCII formatted files where each line of text refers to individual properties and variables of the specific luminaire. Some IES files use data that is relative to the initial rated lumens for the lamp used in the test of the luminaire, others use absolute photometry where the intensity and distribution of the light readings do not depend on a specific lamp. It is the former case where we can modify the IES file. An IES file dependent on the initial rated lumps for the lamp has a line formatted like this (the U4 2x4 2 LAMP' with 4" parabolic louver is used in this example);

2 2950. 1.000000 19 5 1 1 1.750 3.750 .000

where;
  • 2 refers to the number of lamps in the luminaire
  • 2950 refers to the initial lumen output for each lamp in the luminaire
  • 1.000000 is a candela multiplier which multiplies all light intensity readings in the photometric data
  • 19 refers to the number of vertical angles in the photometric data
  • 5 refers to the number of horizontal angles in the photometric data
  • 1 not sure what this refers to
  • 1 refers to the unit measurement used to measure the dimensions of the luminous opening (1=feet, 2=metres)
  • 1.750 refers to the width of the luminous opening
  • 3.750 refers to the length of the luminous opening
  • .000 refers to the height of the luminous opening
This line is normally just after the 'tilt=[some specific value]' line. The important information here is the number of lamps in the luminaire, the initial lumen output for each lamp in the luminaire, and the candela multiplier. So to change our IES file to 14W lamps, we change this line to;

2 1200. 0.406780 19 5 1 1 1.750 3.750 .000

So our 14W lamps each output 1200 lumens of light, and 2x1200 lumens is 40.678% of 2x2950 lumens (2400/5900), so our candela multiplier changes to 0.406780, which will reduce all the light intensity readings in the photometric data down to the approximate (very rough) output of two 1200 lumen lamps.

You can modify IES files by opening them in Notepad for Windows or TextEdit for Mac. Make sure you save the modified file in the original IES format.

Appendix B: IES Alternatives
As you know LightUp uses IES files to load in photometric data, yet some manufacturers don't provide IES photometric files for their luminaires. Another format is IDT (or Eulumdat format file) which is used by programs like DIALux and Relux, and popular with European manufacturers. There are a few programs out there that convert Eulumdat files to IES files; Outro
Well that about wraps up the tutorial. I hope it helps you when you're aiming for efficient office lighting. When LightUp 1.6 comes around I'll write a 'brief' tutorial on daylighting and office lighting that should fill you in on the critical aspects of good and efficient daylighting design, and hopefully lead you to consider great PSALI methods of automated lighting.

I'd love to hear feedback, suggestions and maybe even insults if you're feeling spry.

Thanks for reading.

-Niall

sepo
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Re: Lux Contour Office Analysis Tutorial

Post by sepo » Sun Jul 05, 2009 9:28 am

Very detailed and useful tutorial. Thank you very much. I think you should convert it to PDF.
Saying that I am not quite sure if this is for gallery section. Maybe it is high time is that we get tutorial section on the forum.

bentleykf
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Re: Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 10:05 am

Thanks sepo :) will convert it into pdf.

I second your request for a tutorial section. I was a bit wary about putting it in the Gallery, the Miscellaneous section seems to be filled with bug reports, etc so the relevance isn't really there for a tutorial. Wishlist and announcements are what they are, the gallery is really the only place available for this imo.

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AdamB
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Re: Lux Contour Office Analysis Tutorial

Post by AdamB » Sun Jul 05, 2009 11:01 am

Incredible job there! Great seeing how you're using LightUp too.

As you can see I've moved this thread into the new Tutorials section.

Adam
Developer of LightUp http://www.light-up.co.uk

bentleykf
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Re: Lux Contour Office Analysis Tutorial

Post by bentleykf » Sun Jul 05, 2009 11:13 am

Heh, thanks adam, and thanks again for the tutorial section.

mpaplow
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Re: Lux Contour Office Analysis Tutorial

Post by mpaplow » Sun Feb 21, 2010 9:51 pm

Wonderful tutorial!

I am in the process of designing a school and would like to use Lightup to analyze different design options for optimizing daylighting with or without added light fixtures. While I understand how to use the Alt key to obtain lux readings in the space, which I can convert to footcandles, I do not know how to set up the model and, particulary, Lightup, so that the render will accurately reflect the real-world conditions and results- the various multipliers, screening with AO, etc. I do not want to produce a distorted result that may look attractive but not be physically accurate through ignorance of how to correctly use the application. Our project brief requires daylighting-only analysis to produce certain ranges of illuminance, and we are evaluting different combinations of window sizes and orientations, screening devices, roof monitors, etc, so accurate results are important in helping us make correct design decisions. You had mentioned in a previous post preparing a similar tutorial on daylighting; I would be very grateful for any advice or help anyone could offer!

Thank you in advance;

mp

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Re: Lux Contour Office Analysis Tutorial

Post by AdamB » Thu Feb 25, 2010 9:32 am

mpaplow wrote:Wonderful tutorial!

I am in the process of designing a school and would like to use Lightup to analyze different design options for optimizing daylighting with or without added light fixtures. While I understand how to use the Alt key to obtain lux readings in the space, which I can convert to footcandles, I do not know how to set up the model and, particulary, Lightup, so that the render will accurately reflect the real-world conditions and results- the various multipliers, screening with AO, etc. I do not want to produce a distorted result that may look attractive but not be physically accurate through ignorance of how to correctly use the application. Our project brief requires daylighting-only analysis to produce certain ranges of illuminance, and we are evaluting different combinations of window sizes and orientations, screening devices, roof monitors, etc, so accurate results are important in helping us make correct design decisions. You had mentioned in a previous post preparing a similar tutorial on daylighting; I would be very grateful for any advice or help anyone could offer!

Thank you in advance;

mp
One important thing to point out is that Direct light (Insolation/local lights) analysis is quite different from Daylight analysis.

Direct light analysis uses physically based formulae for calculating lux / Kwh at each point in the model based on the sources illuminating each sample point. Its just cranking the math.

Daylight analysis is a Statistical model of where daylight will bounce around in your model - less light in nooks and crannies further inside your rooms, more light closer to openings/outside. The results are then scaled by some nominal value (default 14000 lux) to give an estimate of how much daylight you'd actually get in your model at any sample point. So it will give you analysis that can help guide your design choices, but it will be conservative because of its simplifying assumptions.

Adam
Developer of LightUp http://www.light-up.co.uk

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