Category Archives: Lighting Design

Informtaion of lighting schemes and architectural lighting together with details of how energy saving light bulbs can contribute to interior design.

How to calculate the LUX level in a Room

Basis of LUX and Lumens

The measurement for the light level encountered in a room or for an exterior space is LUX. The measurement of the light output from a lamp is lumens. Although 1 lumen will theoretically produce 1 LUX of light over an area of 1 square metre this is only in the perfect world as there are other factors to consider. For instance the decor and colouring in the space will undoubtedly result  in some loss of light unless the room was had perfectly reflecting mirrored walls.

The Calculation of LUX level in a room

The LUX level in a room is calculated from the following formula

E(LUX) = F(lm) x UF x MF / A


E is the the LUX level achieved

F is the average lumens value form the light source

UF is the utilisation factor for the space which takes into account the colouring of the surfaces in the space together with the geometry

MF is the maintenance factor for the lamp which allows for a level of light depreciation over time.

It is clear to see from this formula that the light level experienced is reduced by the 2 factors which are the maintenance factor of the lamp and the utilisation factor of the space.

Clearly these values are situation dependent but typical values for these would be 0.4 for the utilisation factor and 0.9 for the maintenance  factor. This means that in a real situation you would achieve typically 35% of the light level that could theoretically be achieved in an optically perfect space.

 What LUX levels are needed in a Room?

The level of LUX needed in a space is obviously subjective but here are some examples to provide some indication of what is needed.

Areas for relaxation for instance lounge or TV rooms would typically have 120 LUX. For an area which where it is necessary to read in it would be advisable to increase this to 200LUX. A domestic office environment of office for occasional use could be illuminated to a level of 250 LUX. It would be advisable to illuminate a commercial office area to a level of 400-500 LUX but where the majority of work is computer based a lower level is acceptable.  For a retail environment where people are purchasing goods then a level of around 500 LUX is typically used. In a work shop area or area where detail work is undertaken then a LUX level of between 500 and 700 is desirable. Within an operating theatre in a hospital a LUX level or around 1000 would typically be used.

Calculation of how many lights are needed in a room?

Simply by turning the formula around it is possible to work out how many lights are needed for a room. This is particularly useful when working our how many spot lights or ceiling lights are needed in a space.

N = Ex A/(FxUFxMF)

So be example for a large space which is 10x 10m with 700 lumens ceiling lights , taking a maintenance factor of 0.9 and a utilisation factor of 0.7 then 45 lights would be needed to provide a LUX level of 200.

For a Kitchen which is 5 x 3 metre and using downlighters which produce 430 lumens output then for 180LUX you would need 14 downlighters taking the same factors as before.

I do hope that helps but of you have any questions please feel free to get in touch with us at SLB for some advise.


This entry was posted in Lighting Design on April 25, 2014 by .

Advise on LED Strip and Fitting It

I have been asked to put together some general advise on LED strip so if you are interested please read on.

LED Tape
Voltage Selection

The first thing to consider is the length of the runs that you are planning to use and the wattage of the LED tape. As a rule of thumb if you are using 14.4W/m strip then it if you go above 5m runs then it is always best to use 24 volt strip. The reason for using 24 volt over 12 volt is quite simply because the current is halved and as a consequence the voltage drop along the strip is reduced. The net benefit is that the strip will be brighter.

Joining LED Strip

LED strip can be cut to almost any length by cutting through the strip at the marked points with a sharp pair of cutters or knife. Once cut if you want to join to pieces together then you can either use the connectors for IP20 strip or solder on short linkage wires. If you want a 100 percent  reliable connection then I would always recommend soldering. now when connecting there is a note of caution that you connect the correct wires together. This means that you have to ensure that you cut the strip at the correct end otherwise your linkage wires will need crossing. This methodology applies to both single colour 2 wire strip and RGB 4 wire.


RGB Strip connection wire colour convention

An easy mistake to make with RGB tape is to connect up the wires incorrectly. So the black is positive or live and then the 3 additional wires are Red, Green and Blue. Do not mix up the Blue and Black!


Sticking Down LED Strip

LED strip does come with a sticky back but this cannot relied on in all situations. For example is you are sticking strip upside down on a horizontal surface then always use some clear silicon to bond the strip to the surface. This will avoid the strip falling off a few days or week later. The other good tip is say you are putting LED strip in the groove around the underside of a kitchen work surface then do not stick the strip to the top of the groove stick it to the outside vertical surface and this means it will hold better and also that it will wash light rays effectively down the cabinet doors.

Dimming  and Colour Control of Long Lengths of Strip or 

If you have a long length of strip which is say single colour which you need to dim and too long for a single driver then the best way to join it is using data repeaters. By using the data repeater you can use an additional driver at the junction point and also ensure that the identical signal in the first length is passed to the second length. This means that when you dim the tape the whole length will dim together. The other useful tip here is that if you are using a 4 channel data repeater then you can link together the RGB outputs and this will mean that the data repeater can take 3 times the load.

For RGB the principle is identical and the data repeater will ensure that the same signal is passed between the strip lengths and what ever shade or colour sequence you have on the first length will be repeated for the next. This principle applies to whatever control method you are using for the RGB tape whether that is simple colour wheel control or DMX.

This entry was posted in Lighting Design on April 8, 2014 by .

The LED Panel

The Rationale behind the LED Panel

In commercial buildings there is no doubt that fluorescent tubes have been an excellent solution.  If you tuck four 600mm tubes behind a 600x600mm ceiling panel you can get good lighting with fair economy and additionally the look is pleasing to the eye. However the look is not perfect because when you look straight up at them you can see the individual tubes which can be slightly disconcerting if you want that very clean consistent contemporary commercial look. Now you can take the obvious step forward by replacing the 4 fluorescent tubes with LED tubes and this will for sure give some significant benefits. The LED tubes are typically 55% more efficient so you will save a significant amount in electricity but additionally  the longer life which is typically 30-50000 hours means they will last around 25 times longer than traditional fluorescent tubes. Also if you are repeatably turning the tubes on and off by for example a motion sensor then this life time difference will be even more because the fluorescent tube life time is significantly shortened by repeated switching. This means that the best way forward is to go for the LED Panel.

The advantages of the LED Panel

AR111 LED lamp
The LED panel is a thin light fitting typically 600x600mm and normally just around 35mm thick. It is illuminated by a vast array of individual LEDs normally of the SMD technology which are hidden behind a frosted front panel. This means that the look is slick with clean visual lines and additionally when turned on you get a nice even consistent radiation of light. This provides a very modern and up to date aesthetic appearance for the 21st century office. Th alternative would be to use four LED tubes but the additional benefit of the LED panel is that the commercials are improved because an LED panel is more cost effective that 4 individual LED tubes. For this reason we are seeing a gradually migration to the LED panel in offices, hospitals, retail outlets and the multitude of commercial buildings that use this form of lighting. The LED panel is not restricted to 600mm square and units are also available in the larger 600x1200mm size which means that the panels can span 2 ceiling tiles. This means that the scale of the economy is even greater then using multiple LED tubes.

Emergency Back up LED Panels

In most commercial buildings then a percentage of your lights will need emergency back up. This means that in the eventuality of a power failure then you do not loose all light which would clearly by a hazard particularly in places like hospitals or nursing homes. The normal requirement is to have a 3 hour emergency backup solution so that light can be preserved at a reduced but acceptable light level for over 180 minutes. The benefit if the LED solution here is that because the LED has a lower power consumption then the size of emergency backup battery is considerably reduce compared to fluorescent light sources. However you will need to ensure that the backup solution has the correct driver for the Emergency LED panel.

This entry was posted in Lighting Design on July 22, 2012 by .

The Premier Chandelier LED Bulb

The Issue with  LED Bulbs and Chandeliers

It is not an easy task finding good LED Bulbs for Chandeliers. The fundamental issue is that Energy Saving Light Bulbs by their very nature are not good looking and LED bulbs as the ultimate classification of energy saving light bulbs are no exception. Chandeliers were originally designed for candles which were lit when it went dark and to reproduce this authentic look candle light bulbs were introduced to have similar aesthetics. With the traditional filament bulb then the light is radiated from the brightly glowing filament and this is cast through a clear glass casing and onto the chandelier crystals. This has the effect of maximising the sparkle from the crystals and produces a very pleasing overall effect.

The issue arrives when this effect is replicated with  LED bulbs . The LED bulb can either be made as a multiple LED candle bulb or a high powered LED bulb which will have one two or three single LED’s. The multiple LED candle bulbs are cost effective and they do produce a good light output and they are pretty compact in size so from a functional perpective they are ideal. However there are 2 dissadvantage. Firstly, the technology does not allow them normally to be dimmable and secondly, the look is very high tech and accordingly does not complement traditional chandeliers well.

Manufacturers then tried to disguise the multiple LED usage whether that be 40 LED’s or just 3 LED’s by making a frosted casing which then does not work well with chandeliers because the frosted casing means that you do not get the enhancement in sparkle from the crystals. Then to top it all some manufacturers produce the flame tip LED candle bulb but they are so bulky and large that the effect does not sit well with the aesthetics of the chandelier.

The New Invention in LED Candle Bulbs

However now there is a hot new product which can be seen on this candelabra. It is the LED bulb with the gold casing at the front.
LED Candle Bulb

This lamp has a single high powered LED and utilises a revolutionary light tube which channels and radiates the light producing an effect very much like a traditional filament light bulb. Additionally the bulb utilises the CREE chip which means that the LED does produce a very consistent colour temperature unlike some of the cheaper alternatives and the icing on the cake is that the LED bulb is dimmable. The CREE chip is also very reliable so you can realistically expect to get the 30000 hour life expectancy fro this light bulb unlike with many lamps which are rated with a high life but you still get some early failures. For bulbs which are easily accessible this is normally acceptable but a chandelier can be hung high above a staircase or in a gable roof which means that getting access to change a light bulb can be a problem!

Clearly this LED candle bulb is not for everybody because of the high investment cost and if you have a chandelier with 30 bulbs then the investment is certainly significant. However, if you want top quality combined with good aesthetics then this LED lamp is certainly worth serious consideration.

This entry was posted in Lighting Design on July 6, 2011 by .

How many downlighters should I use?

If you currently have standard pendant lighting or wall lights and are converting to downlighters then it is important to get the right amount of spot lights so that the space has the correct light level. It is especially critical with the recessed spot lights for instance halogen MR16 bulbs as these involve cutting round holes in your plasterboard ceiling and this means that relocating them would be a major job. So make some calculations and get it right first time! The other consideration is that if you are starting with say 50W halogen downlighters and planning to migrate to LED Bulbs for energy efficiency reasons, then the LED bulbs are generally not as bright so you will invariably need to use more.

Downlighter Spacing Calculations

If a lighting architect was  to do a true theoretical calculation then he would start with the LUX level required for the room and from this work out the lumen’s value needed from the luminaires. This is quite complex because you need to take into account a whole range of factors like wall colours and  the directional aspects of the lighting. Then after deducing the lumen’s needed  the specific light bulbs can be selected. This may sound great but the issue is that most of the variability comes with deducing the lighting level variation caused by factors such as the wall, work surface and flooring colours which means that as a result the calculation is only an indication. Accordingly  I would propose that you use some rule of thumb indicators to work out how many downlighter are needed.

The first rule of thumb is that for a normal living area you need approximately 1 watt of light per square foot and for a work area where clarity of illumination is important,  for instance a kitchen, them it is best to have between 1.5 and 2 watts per square foot. Now this wattage is assuming that you use the normal halogen downlighters and not low energy halogens or CFL or indeed LED bulbs. Clearly if you had 1 watt per square metre of LED light then the room would be dazzlingly bright!

Calculation of the number of lights needed  for a Living Area

If we take a large kitchen, breakfast room area of size 5 by 7 metres then at 1 watt per square foot this would mean that you need 377 watts of lighting. This could be accommodated by using different configurations.

1. Use 8 x 50watt dowlighter in 2 rows of 4 giving 400 watts of lighting.

2. Use 12 x  35 watt downlighter in 3 rows of 4 giving 420 watts of lighting.

3. Use 15 x 25 watt downlighters in 3 rows of 5 to give 375 watts of lighting.

This gives you a starting point but then you need to take into account other factors to tune the number.

If you have a higher than average ceiling height then it is best to increase the number slightly as downlighters illuminate best at a height of about 1.5-2 meters. The other important consideration is what other lighting you have in the space. For example if you have under cupboard lighting and a cooker hood light then you can reduce the number slightly. Also as discussed earlier then the wall, floor and work surface colour will make a significant difference so if you have darker mat  colours in your design scheme then you will need to increase the illumination level.

The  other rule of thumb cross check is that the saving will typically be  between 1.4 and 1.6 meters for the 50watt equivalent downlighters which should enable a cross check to be performed before those holes are made in your plasterboard. So that is it,  but as a closing remark with my eco hat on then you need to convert the halogen wattage levels to LED or CFL equivalents. So a 25watt halogen is broadly equivalent to a 3 watt LED and a 7watt CFL MR16 is broadly equivalent to a 35watt halogen.


Calculation of the number of lights needed  for a Kitchen Area

So if we take the kitchen areas then it would be appropriate to use the equivalent of 15 x 50w halogen downlighters. This means that for the size of 5 x 7 m then 3 rows of 5 would give a high level of illumination suitable for a work area.

This equates to a closer spacing of between 1.2 and 1.25m.

Now is you are using a good quality high output 5w COB GU10 then then these can generally replace a 50w halogen on a 1:1 basis.

How many  Lumens Output per Square Metre are needed.

With the complication of LED technology always improving and the lumens output per watt going up with the new COB LEDs it is often more meaningful to use lumens as the base measure for light output. Using the calculation from before with our 5 x 7m room we get the following results:-

For a living area level illumination then approx 4000 lumens for 35 square metres which is 115 lumens/ metre.

For a work area level illumination which requires very bright light then this should be increased to 7500 lumens which equates to 215 lumens/metre.



This entry was posted in Lighting Design on September 6, 2010 by .

Choosing the right light bulbs for your Chandelier

You have just purchased that fabulous chandelier that you have been mulling over for ages. The cost was high but you convinced yourself that it is a sound investment and you went for a high quality chandelier on the basis that it would be in the family for generations to come. The chandelier is grandiose and ornamented with a multitude of crystal trimmings that reflect light with all colours of the rainbow in a beautiful fashion around the hallway. You have the perfect position for the chandelier and you have carefully chosen your design scheme to complement the traditional elegance of the chandelier. The only issue is that it has 24 light bulbs which if you calculate the power consumption at 40 watts a light bulb is a massive 960 watts which is nearly a kilowatt. That is the power consumption of an electric heater which cannot be good for your electricity bills or indeed for the environment. So what do you do.?
Lets look at some of the choices.

Halogen Bulbs

Halogen Bulbs are definitely the perfect solution from an aesthetic perspective . halogen bulbs in chandelier. The simple clear lines and elegant flame tip of the candle bulb complement the chandelier and the clear bright light will ensure that you maximise the sparkle from the crystal. So now you have the perfect light bulb from visual point of view and the halogen bulb will save 30% in energy when compared to traditional incandescent bulbs. But that is still a lot of power so the answer here is to fit a dimmer switch and use dimmable halogen bulbs and this way you can not only adjust the light level to the perfect setting, but also you will save energy. Just a word of warning, make sure that the wattage rating of your dimmer switch is sufficient for all your halogen bulbs.


If your focus is to save more energy saving both in electircity costs and contributing further to environmental sustainability then you will need to move to CFL technology and go for a energy saving candle bulb with a flame tip. The looks are not as good as the halogen bulb but the CFL will save you a much greater 80% in energy costs against the traditional filament light bulb.

LED Bulbs

If you are looking for the ultimate in energy conservation then you need to go for a LED bulb and if you select the LED Candle Bulbs with a flame tip. Again the bulb is not quite so elegant as the halogen as is is slightly broader and these ones have a multitude of separate LED lights which give a high technology appearance but the environmental benefits are most impressive. These bulbs only consume 3 watts in power each and will produce the light output of a traditional 25 watt light bulb so for our 24 light chandelier example that is 72 watts consumption against 600 watts which is simply amazing.

This entry was posted in Lighting Design on July 6, 2010 by .

Choosing Energy Saving Bulbs for Interior Design

So you have created your fabulous interior design scheme with carefully chosen wall coverings, selected furniture and those most elegant lighting fixtures. Now you do not want to go and ruin it all by adding some ugly light bubs. There are certainly some most awful looking energy saving light bulbs on the market for instance the linear design CFL’s which have the straight fluorescent tubes which go up vertically and then simply loop back. These light bulbs are just perfect if they are hidden away in the depths of some lighting fixture and never to be seen by the naked eye, but to have them visible in any room apart from a garage or a work area has got to be forbidden.
Now the situation is still further complicated because there are different types of energy saving light bulbs , namely , CFL, Halogen Bulbs and LED Bulbs , each of which have different efficiency levels and different levels of environmental friendliness. So if the environment is on the agenda for your design scheme then the decision is far from simple.
So what are the choices?

Halogen Light Bulbs

Halogen Bulbs are the baseline for energy saving light bulbs offering a 30% saving in energy efficiency over the traditional incandescent filament bulb and very similar aesthetics. So if you need a light bulb of small proportions to fit into that elegant ceiling light then choose a halogen golf ball which will complement it. Or alternatively if you have spot lamps then a halogen spot is a good looking bulb with clean crisp lines.


The compact fluorescent lamp or CFL has far higher energy efficiency offering a 80% saving in energy over the traditional filament bulb. However the aesthetics and design looks can be questionable! The linear CFL is definitely ugly and has been improved by the full sprial bulb, which is an improvement but still not right where aesthetics are of key importance. The answer here is to go for the Globe Bulb which has an energy saving spiral inside and an aesthetic glass globe on the outside. This way you get the energy saving benefits of the CFL and will only lose a small amount of efficiency by light absorption in the glass globe. Then from an aesthetic perspective pick a light bulb with a nice big spherical shaped globe and you are onto a winner.

LED Bulbs

LED bulbs do offer the ultimate in energy savings, saving a massive 90% over the traditional incandescent filament light bulb and the aethetics can be quite good. The LED bulb does look more high tech, but this might be a good thing as long as you build it into your design theme. Here we will just look at spotlights which are the MR16 and GU10 specification light bulbs which fit ino a multitude of downlighters and directional spotlights. There are 2 different types of these LED Bulbs either with multiple LED’s typically 80 for a 3w bulb or ones with high powered LED’s typically 3 single 1w LED’s. The choice is largely an aesthetic one with the multiple LED lamps looking very futuristic and the high powered 3x1w LED’s giving a nice clean simplistic appearance.

This entry was posted in Lighting Design on July 6, 2010 by .