Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

The Effect of Using LED Lighting on Future Vessels O J Simmonds*, MEng; Lt F W J de Wildt†, MSc RNLN †

*BMT Defence Services Ltd, Bath, UK MOD, Defence Equipment and Support, Bristol, UK

SYNOPSIS On modern vessels, both naval and commercial, lighting accounts for a significant use of energy. This paper investigates the benefits and savings that can be had from using modern LED (Light Emitting Diode) lighting to replacing conventional fluorescent, tungsten and halogen bulbs. Over the last ten years there have been significant advances in LED emitter technology; their light output now rivals halogen bulbs at a third of the energy usage. This can result in significant through life savings as less fuel has to be used to produce energy to meet the lighting demands.

INTRODUCTION Light Emitting Diodes (LEDs) will soon be the future of maritime lighting on board all types of vessel. They are already widely used on commercial cruise liners for decorative effects; however this paper serves to prove that LEDs offer substantial through life cost savings and will reduce vessel fuel consumption. To date LEDs are seen as novel and expensive forms of lighting, however the efficiency and through life cost effectiveness of LED lighting systems will drive demand for more affordable LED lights. The aim of this paper is to present a high level analysis of the comparison between different light types that could be used on marine vessels. The model presented is only simple and was produced to enable a quantitative assessment of the required number of lights to be installed in a given ship space.

HISTORIC LIGHT TYPES Three types of historic lighting have been considered in this paper to serve as the benchmarks to which Light Emitting Diodes (LEDs) can be compared. Tungsten Incandescent Historically Tungsten Incandescent light bulbs have been used extensively on board maritime vessels for many years. The light bulb works by heating a thin filament to produce light by passing an electric current through it. The filament is enclosed in a glass bulb that contains either a vacuum or an inert gas to prevent oxidation and failure of the hot filament. Halogen A halogen lamp is an incandescent lamp with the tungsten filament enclosed in a glass bulb containing a small amount of halogen gas such as iodine or bromine. The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle that increases the lifetime of the bulb and prevents its darkening. The halogen lamp can operate its filament at a higher temperature, thus increasing its luminous efficacy compared to a standard gas filled lamp of similar power without loss of operating life. Authors biography

Oliver Simmonds joined BMT Defence Services in September 2008 having completed a Masters degree in Mechanical Engineering at the University of Bath. He is currently working towards an MSc in Electrical Power Systems. Since joining BMT he has been the lead in several projects ranging from the investigation into future power distribution systems to arc flash studies. Lt Frans de Wildt earned an MSc in Mechanical Engineering at Delft University of Technology. He served in two engineering posts at sea in the RNLN and briefly worked for the Defence Materiel Organisation of the Ministry of Defence of The Netherlands before he got posted in the UK. He is currently project manager in the Programmes and Technology Group of Defence Equipment and Support in the UK in which he manages R&D projects on integrated electric propulsion, power system architectures and automation.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. Fluorescent A fluorescent tube is a type of gas-discharge lamp that uses electricity to excite mercury vapour. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. They produce light much more efficiently than incandescent bulbs, however they are more complicated as they require a starter ballast to provide the initial striking voltage required to start the arc discharge and therefore usually have a higher initial procurement cost.

ADVANTAGES OF LED LIGHTING LEDs are solid state semiconductor devices and the illumination is achieved when a semiconductor crystal is excited so that it directly produces visible light. This section discusses some of the main advantages that LED lights offer over the other types of lighting available. Energy Efficient LEDs are much more energy efficient than other types of lights as can be seen in Table I. It should be noted that despite the differing light output and power consumption values presented, the resultant efficiency values are fairly constant for each light type throughout the lumens range. This provides the opportunity to not only reduce energy bills but also provide a greener source of lighting. Typical Output (lumens)

Power Consumption (watts)

Efficiency (lumens/watt)

Tungsten Incandescent

800

60

13.3

Halogen

1430

50

28.6

Fluorescent

1150

18

63.9

Light Emitting Diode (LED)

900

10

90.0

Light Type

Table I Comparison of Lighting Efficiency

Long Life LED can last up to 25 times longer than incandescent light bulbs (LEDs have an estimated life of 30,000-50,000 hours, compared to 1,000-2,000 hours for standard incandescent bulbs). This not only greatly reduces the maintenance burden, both in costs and man-hours, especially where bulbs or fittings are in difficult to reach places but also reduces the amount of spares required to be stored onboard. Additionally LEDs slowly fade over time rather than suddenly burning out like tungsten sources, therefore allowing maintenance to be planned in advance. Durable LEDs are highly rugged solid state devices with no filament that can be damaged due to shock and vibrations. In a maritime platform, especially a warship, this is a significant advantage. Compact Especially compared to fluorescent tubes, LEDs are very small and so can be installed in areas of limited accessibility. Combined with their ability to produce very directional light output compared to incandescent or fluorescent bulbs if required, means light can be directed exactly where required. Instant Light Unlike fluorescent bulbs, which can take up to several minutes to reach full brightness, LEDs light instantly and have no warm-up time.

MODELLING APPROACH To be able to make a cost comparison of the different types of lighting, power consumption and efficiency alone is not sufficient. The number of light fittings to meet the required Illuminance of each compartment is essential as well. To establish the number of light fittings a MATLAB model has been produced.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. The model used for this analysis has been built up in two parts; firstly a model of a single light fitting, and secondly a model of a room with multiple light fittings. Within the model the lights have been defined as having a set value of Luminous Flux (Unit: lumen, Symbol: lm) and the rooms have been modelled with a requirement for a certain value of Illuminance (Unit: lux, Symbol: lx). One lux is equal to one lumen per square metre. Single Light Model The single light model has made a number of key assumptions listed as follows: The model assumed that the light modelled was a point source. The light fitting reflector is assumed to be a perfect reflector and so all the light produced by the light emitter is reflected out of the fitting. Taking account of these assumptions a model of the single light fitting could be produced over a number of steps. A point light source in free space will emit light in all directions in a spherical pattern. At a distance of 1m from the light (i.e. r = 1) the area covered by the light is equal to 4π, shown as follows:

4 r 2 ; If r 1, then surface area

Surface Area of Sphere

4

If the light source is initially assumed to output 1000 lumens, at a distance of 1 meter from the light the level of lux will equal:

Lux

Lumens Area m 2

1000 4 12

1000 4

79.6lx

From these two equations it can be seen that Illuminance is effectively inversely proportional to the square of the distance:

Lux

A

Lumens r2

120º

A

Figure 1 Output from a Single Light Fitting

A simple point light source with a 120º reflector was then modelled, as shown in Figure 1. All of the light is now emitted over a smaller area that can be shown to equal πr2, using the solid angle formula.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

Figure 2 Pictorial representation of the Solid Angle in a Sphere

The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point and its formula for a sphere is as follows, where = the half angle of the resultant cone, in this case 60º. Figure 2 shows a pictorial representation of the solid angle in a sphere.

2 1 cos If a 1000 lumen light source is again assumed and a distance of 1 meter then the lux level along the curved path (A-A) will be equal to:

Lux

1000 12

1000

318.3lx

120º A

60º

A

B

B Figure 3 Total Coverage from a Single Light Fitting

However the majority of this area is in free space and not on the flat plane (B-B) that the light would cover as shown in Figure 3. The Illuminance on the flat surface at point B can be calculated as follows using Figure 4 for clarity:

O

60º

A

B

A Figure 4 Calculation of Total Light Coverage

Using simple trigonometry the distance OB is equal to:

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

cos 60

OA OB

OB

OA cos 60

OA 0.5

OB

2OA

The distance OB is twice that of OA, and therefore the Illuminance at point B will be a quarter of that at point A because Illuminance has been shown to be inversely proportional to the square of the distance. The final step of the single light model is to calculate the resultant lux level acting perpendicular to the flat surface as shown in Figure 5.

120º 60º B

B Figure 5 Total Coverage from a Single Light Fitting Perpendicular to Working Plane

Using simple trigonometry of vectors it can be seen that at point B the Illuminance perpendicular to the surface is equal to the Illuminance direct from the light source multiplied by the cosine of the angle (for point B this is 60º) Therefore at any point along the flat surface (B-B) the Illuminance has been shown to equal:

Lux Where

Solid Angle

2 1 cos

and

Lumens cos 3 2 r = half angle of the resultant cone.

Putting all these equations into a MATLAB model produces the output as shown in Figure 6. This shows the light output from a single fitting of 1000 lumens and a 90º reflector angle. The working plane is at 1.5m and initially outside the reflector the lux level is modelled to be zero.

Figure 6 MATLAB Lighting Model Output for One Light Fitting

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

Multi Light Model Once a single light has been modelled, in order to find out how well this light provides lumination for a room, a model had to be created. The purpose was to calculate the number of lights that were required to light a room to a sufficient Illuminance value, for different types of lights. As multiple lights are placed into a virtual room, the areas that are luminated by the lights will overlap. Luminance values can be linearly added together, to find an overall value. In reality there is reflection of light off all of the surfaces of the room, which contributes to the luminance at any position in the room. Multiple light models of rooms can vary greatly in complexity from simple spreadsheets to complicated 3D graphics engines used in computer games and animation. This program was designed to be accurate enough to draw some useful conclusions with graphical solutions, but without the expense of the other options. In order to do this several assumptions had to be made. To keep the rendering time of the model down, outside the direct rays of the light the room is assumed to be completely dark. In order to better approach reality, two factors within the model were created to expand the overall spread of the light; an inner spill factor and an outer spill factor. Taking these two factors into account produces a new output curve for the light emitted from a single fitting. It is effectively the original curve produced and shown in Figure 6, with two additional ‘spill’ zones added. The inner and outer ‘spill’ zones were assumed to be an extra 20% and 40% respectively of the reflector angle, however with a 30% and 60% reduction in light output respectively. Figure 7 shows this pictorially and the new curve produced can be seen in Figure 8.

+20% +20%

Outer ‘Spill’

Inner ‘Spill’

αº

+20% +20%

Main ‘Hotspot’

Inner ‘Spill’

Outer ‘Spill’

Figure 7 Additional Spread of Light from a Single Fitting

Figure 8 MATLAB Lighting Model Output for a Single Fitting with the Light Spill Factors Included

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. The program does model reflections off the walls of the room; however there are some assumptions that are made in the calculations. As the walls are not mirrors and are rough surfaces there will be a reduction in the strength of the light that is reflected. In reality rough surfaces reflect light off walls in random and non-uniform ways, however in this program this has been simplified. For any point in the room the corresponding indirect illuminance for the reflected light is multiplied by a reflection factor. This is then added to the direct illuminance from the light fitting. This is shown in Figure 9. Light Source Direct Illuminance (lux)

Pixel

Indirect Illuminance (lux)

The indirect illuminance is the illuminance resulting from the indirect path distance multiplied by the reflection factor

Figure 9 Effect of Direct and Indirect Light on a Single Area

As is stated above the reflection off the walls has been taken into account, with certain assumptions. However in certain conditions the light from a source could reflect off several walls and still have some relevance. This program however does not take this into account. In some circumstances this could have an impact, such as modelling a corridor where the walls are quite close together. The program does not do this in order to keep the speed of rendering down. Using these assumptions a useful and generally accurate program can be produced, to create a lighting arrangement to fill a room to a certain level of luminance. The model can be changed in several ways so that the room and the individual lights can be customised to individual requirements. These are: Room Width Room Length Room Height Reflection Factor Lumens Value Reflector Angle Inner & Outer Spill Factors

- Width of the room in metres - Length of the room in metres - Height of the room above the working plane of interest in metres - Of the Walls of the room - Of the light source - Of the light fitting in degrees - Percentage of reflector angle and Light output reduction factor

Using the method discussed a resultant matrix of the Illuminance values seen on the working plane could be produced, Figure 10 shows this graphically.

Figure 10 Compartment Model with One Light Fitting

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. LIGHTING MODEL Input Data Two generic ship spaces were modelled using the techniques described earlier. The details of these are given in Table II. One was a long and thin space to represent a typical passageway, and the other was larger and represented a typical compartment.

Space Modelled

Length (metres)

Width (metres)

Height (metres above working plane)

Required Illuminance (lux)

10

1.5

2.5

75

8

6

1.5

150

Passageway Compartment

Table II Details of Compartments Modelled

The height used in the model is the height of the space above the working plane of interest in metres. In the passageway this was the floor and so was 2.5m, and in the compartment it was assumed that there was a typical desk height of 1m and so the height was 1.5m. The value for the required illuminance was taken from a Ministry of Defence published standard for the lighting requirements of surface ships [1]. It should be noted that the values given are the same as those for Commercial vessels [2] and as published for NATO vessels [3]. The reflection value used for both spaces was 20% which is at the lower end of the range of values for a dark grey matt surface. The lower end of the range was used to take into account items of equipment on the walls and a general build up of contaminates through life further reducing the reflectivity. [4] For the two generic spaces modelled, five lighting types were considered covering the four main types of light previously discussed. The details of these are given in Table III. The data has come from an average of several different manufacturers’ data in order to produce a generic light model of each type. Light Output (lumens)

Reflector Angle (degrees)

Electrical Power (watts)

Efficiency (lumens per watt)

Typical Light Cost (GBP)

Lifetime (hours)

Tungsten Incandescent

800

120

60

13.3

0.50

1000

Halogen

1430

60

50

28.6

2.00

5000

Fluorescent

1150

120

18

63.9

1.00

20000

Multi-LED (Five x 1 watt) Single LED (One x 10 watt)

500

80

5

83.3

10.00

35000

900

130

10

90.0

15.00

50000

Light Modelled

Table III Details of Light Types Modelled

Once the required number of lights for each generic space is known a cost model can be developed to calculate the potential savings that could be had for switching to LED light fittings. Assumptions were made for the cost of fuel at sea (£430/tonne [5]) and the specific fuel consumption of a generator (220g/kWh). This value is representative of current diesel generators, with a slight margin added to cover performance degradation. Using these values a cost model could be created, which gives a representative cost of £0.10 per kWh.

Light Model Output The modelling approach previously discussed was used to model the two different generic spaces for each of the five types of light. The model was run until the minimum lux level across the entire working plane of the space (i.e. the floor of the passageway and the worktops in the compartment) was met with the minimum number of evenly spaced light fittings. The model assumes that the lights on the vessel are on 24 hours a day and 365 days a year and the Tungsten Incandescent light bulb was used as the baseline for the comparison of both generic spaces. Table IV shows the model output for the Passageway. There is no difference in the number of lights required because the shape of the space modelled is long and thin, and the model developed does not take into account

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. light reflected off more than one surface. However this does allow a direct comparison between the different types of light fitting if they were replaced in a space on a one-for-one basis.

Space Modelled

Light Modelled

Number of Light Fittings

Total Electrical Power (watts)

Total Cost of Luminaires (per Year)

Running Cost of Luminaires (per Year)

Total Cost (per Year)

Per Year Cost Saving (%)

5

300

£21.90

£260.17

£282.07

0.0%

5

250

£17.52

£216.81

£234.33

16.9%

Passageway

Tungsten Incandescent Halogen

Passageway

Fluorescent

5

90

£2.19

£78.05

£80.24

71.6%

Passageway

Multi-LED

5

30

£12.51

£26.02

£38.53

86.3%

Passageway

Single LED

5

50

£13.14

£43.36

£56.50

80.0%

Passageway

Table IV Output of Light Model for the Passageway

As can be seen in Table IV there is a significant saving to be had from using LEDs compared to Tungsten Incandescent and even Florescent for a direct one-for-one replacement. The graphical output of the passageway model using five single LED light fittings can be seen in Figure 11.

Figure 11 Graphical output of the Passageway Lighting Model

Table V shows the model output for the Compartment, and it can be seen that there is quite a difference in how many lights are required in the space to light it sufficiently.

Space Modelled

Light Modelled

Number of Light Fittings

Total Electrical Power (watts)

Total Cost of Luminaires (per Year)

Running Cost of Luminaires (per Year)

Total Cost (per Year)

Per Year Cost Saving (%)

16

960

£70.08

£832.55

£902.63

0.0%

16

800

£56.06

£693.79

£749.86

16.9%

Compartment

Tungsten Incandescent Halogen

Compartment

Fluorescent

9

162

£3.94

£140.49

£144.43

84.0%

Compartment

Multi-LED

18

108

£45.05

£93.66

£138.71

84.6%

Compartment

Single LED

12

120

£31.54

£104.07

£135.60

85.0%

Compartment

Table V Output of Light Model for the Compartment

This shows a less obvious advantage of LED over Fluorescent, however both types show clear benefits compared to Tungsten Incandescent. The graphical output of the compartment model using twelve single LED light fittings can be seen in Figure 12. In this figure the interaction between light fittings can be clearly seen on the working plane.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

Figure 12 Graphical output of the Compartment Lighting Model

MARITIME APPLICABILTY In the previous sections four different types of lights are discussed and modelled. Nowadays most maritime vessels already use fluorescent lighting as standard and incandescent light types are being phased out. Traditionally LEDs have not been used on Maritime vessels to date due to their associated high cost which drives up the Ultimate Purchase Cost (UPC) of the vessel. Additionally LEDs have historically not been able to reproduce a similar colour of light to fluorescent and so their use has been avoided. Developments in current technology mean that LEDs can be manufactured to produce colour temperatures close to that of natural daylight (around 6500K) [6], however they are more expensive. Furthermore LEDs are currently only manufactured in relatively small quantities compared to Fluorescent tubes and so cost of manufacturing is relatively high, but manufacturers claim production will increase considerably in the near future, further lowering prices. Light Model Output To be able to make a more fair cost comparison for the maritime sector, Fluorescent lights being the current standard has to be taken into account. Table VI and Table VII show the results of the modelling approach as described in previous sections, but with Fluorescent lights as the baseline for comparison. Number of Light Fittings

Total Cost (per Year)

Per Year Cost Saving (%)

Fluorescent

5

£80.24

0.0%

Passageway

Multi-LED

5

£38.53

52.0%

Passageway

Single LED

5

£56.50

29.6%

Space Modelled

Light Modelled

Passageway

Table VI Output of Light Model for the Passageway with Fluorescent Lights as a Baseline

As can be seen in Table VI, replacing Fluorescent lights by LEDs offer significant annual cost savings of 30% to 50%. Due to the characteristics of a passageway the number of light fittings is equal in all cases, making passageways ideal candidates for refitting LED lighting into legacy ships as well.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May. Number of Light Fittings

Total Cost (per Year)

Per Year Cost Saving (%)

Fluorescent

9

£144.43

0.0%

Compartment

Multi-LED

18

£138.71

4.0%

Compartment

Single LED

12

£135.60

6.1%

Space Modelled

Light Modelled

Compartment

Table VII Output of Light Model for the Compartment with Fluorescent Lights as a Baseline

Table VII shows that due to the higher number of light fittings to meet the required Illuminance in the Compartment, LEDs offer much less of a saving compared to Fluorescent Lighting, typically 4-6%. However, in equal costing scores, LEDs offer additional benefits which could shift the balance in favour of LED lighting. Advantages in the Maritime Environment As discussed earlier in this paper, LEDs are highly rugged solid state devices. This has the advantage of being highly resilient against shock and vibrations, which makes it an exceptional suitable candidate for the maritime (and naval) environment. The inherent longer life of LEDs, in combination with the higher resilience against shock and vibration, offers other benefits besides the obvious cost savings for replacement of the lights as taken into account in the modelling section. Changing a light on a ship can be a very time consuming and tedious task, especially since light fittings are often not within reach or in a watertight enclosure. LEDs last 2 to 3 times longer than Fluorescent lights, which directly results in man-hour savings, but also reducing the amount of spares required to store onboard (resulting in space and weight savings). Another advantage of LED lighting is the small amount of generated heat. Generating as little heat as possible on ships is important to reduce both the required installed cooling capacity as well as the fire hazard which coincide with installing a heat source in false ceilings. As can be seen in Table I, LEDs not only use less energy to achieve comparable Illuminance, they are more efficient as well. Both characteristics of LED lighting contribute to a minimal production of heat. Ships compartments are often full of clutter and have limited spaces to fit lighting. Due to its compact build, LED lighting not only occupies little space and keeps the overall weight to a minimum, but it also allows for installing it in more places compared to Fluorescent lights and with its capability to produce very directional light, LEDs can provide the required lighting within the entire compartment. Overall it can be stated that the introduction of LEDs leads to a reduction of carbon footprint. With ‘Green Ship’ being very topical, LED lighting reduces the carbon footprint by its low energy consumption, high efficiency, low weight (both installed and spare lights) and reduced cooling requirements compared to currently used lights. Applicability Options For all of the reasons discussed in this paper LEDs would be suitable and of benefit for the lighting requirements of future maritime vessels. However LEDs aren’t only applicable to new-build vessels, but are a suitable candidate for refit as well. In order to maximise the benefits offered by LEDs and simplify the refit, ideally LEDs would replace Fluorescent lights on a one-to-one basis. However the model has already shown that for a generic ship compartment 12 LEDs would be required compared to 9 Fluorescent light fittings. If fewer LEDs were used, then the minimum required value of Illumination, in this case 150 lux, could not be met.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

Figure 13 Area of Refit Compartment that Meets Minimum Illuminance Level (150 Lux)

Figure 13 shows the areas of the compartment that would receive 150 lux or over, highlighted green. If the minimum required value of Illuminance for the compartment was reduced to 115 lux, then 9 LEDs would in fact be sufficient. This compromise would be something that would need to be considered when looking at a refit to legacy vessels; however it should be noted that the use of LEDs for a legacy vessel would still provide all of the other benefits discussed previously.

CONCLUSIONS The paper has presented a high level analysis of the comparison between different light types that could be used on marine vessels. It has highlighted the benefits to be had from using LEDs for lighting on maritime vessels and from the investigation carried out the following conclusions can be made: 1.

The LED technology has developed significantly in recent years and is almost at the stage where conventional lights could be replaced on a like-for-like basis with LEDs.

2.

There is a notable through life cost benefit to be had from using LED lights compared to other tradition light types.

3.

In addition to the cost benefit, there are several other benefits (none the least being a reduced carbon footprint) to be had from using LEDs in maritime vessels, with some especially suitable for naval vessels.

RECOMMENDATION It is the recommendation of the authors that LEDs should be adopted for the future lighting requirements of maritime vessels and considered as a refit to legacy fleet. It is felt that the further developments of LEDs will seek to improve their light output and that the increased usage of LEDs will lead to reduced initial costs, therefore making them the obvious choice to replace Fluorescent light fittings.

ACKNOLWEDGEMENTS The authors would like to thank Matt Edgar of BMT Defence Services for his help developing the MATLAB code for the modelling approach using in this study.

Paper presented at the IMAREST's 10th International Naval Engineering Conference and Exhibition entitled `The Affordable Future Fleet' in May.

REFERENCES [1] MoD Defence Standard 02-587, Requirements for Lighting Systems Part 1: Surface Ships, Issue 3 Publication Date 19 December 2008. [2] Lloyd’s Register Rules and Regulations for the Classification of Naval Ships, Vol.2, Part 10, Chapter 1, Section 12. Publication Date May 2008 [3] ANEP 77 – NAVAL SHIP CODE – Chapter V Electrical systems – Regulation 9 Lighting System. Publication Date December 2009 [4] LuxRender Manual, Commercial (www.luxrender.net/v/manual)

Lighting

Rendering

Software.

Available

Online

[5] Data provided by the Ministry of Defence Cost Assurance Services Forecast Group, January 2009 [6] Boyd, J., Let There Be (a New Kind of) Light, IEEE Spectrum News Article, July 2007

at