Downlighter Spacings

I regularly get asked how far apart to put downlighters, so here’s a short article giving some information on light levels and spacings.

The spacing of light fittings has a dramatic effect on light levels. So first we must determine the light level we require. The CIBSE (Chatered Institute of Building Services Engineers) produce guidlines as to recommended lighting levels within buildings, it is summarised here – CIBSE code for interior lighting.

From this I recommend the following general levels

Kitchen and living areas 200 – 300lux

Bathrooms, tolilets 150lux

Bedrooms 150lux + local task liighting

Corridors, hallways 100lux

Let’s take a square area and try various spacings and see what light level we may achieve. For this I use a lighting simulation software called Relux, it can be downloaded free here. All plots are based on a 50w 35 degree GU10 halogen lamp.

Using 1M spacings gives 267lux average (click to enlarge thumbnail)


Using 1.2M spacings gives 171lux average


Using 1.5M sapacings gives 121lux average


Using 1.7M spacings gives 98 lux average


So as a rough rule of thumb we can say kitchens and living areas use 1M spacings. Bathrooms, toilets & bedrooms you can use 1.2M or possibly a bit more. And corridors, hallways etc. you can get away with 1.7M.

For guidance on using an LED GU10 lamp in place of a halogen see my test LED v halogen.


Are cheap SMD LED lamps any good?

Are Cheap SMD LED Lamps any good? Here we test a cheap SMD GU10 LED lamp against a more expensive Kosnic GU10 LED and a very expensive Phillips GU10 LED lamp.

Lamps tested

5050 24SMD 6400K daylight SMD LED lamp – retail price around £4.00

Kosnic KLED05PWR/GU10 5w LED 4000K cool white 36degree 320lumens – retails price around £8 -£9

Phillips MasterLED 6w GU10 2700K 40degree 2700K warm white retail price around £18

Readings Lux

Lamp 0 degrees 20 degrees 30 degrees
5050 24 SMD £4 30 21 15
Kosnic £8-£9 207 33 3
Phillips £18 231 55 19
The SMD lamps performs okay at 30 degrees but performance directly below the lamp is very poor in comparison to the two more expensive lamps. The Phillips perfoms best of all but you would expect that as it costs twice as much as the Kosnic and more than 4 times more than the SMD!
Although the SMD lamp performed reasonably at wider beam angles the fact that it produced such little output directly beneath the lamp would mean it would perform very poorly if used as a replacement for a halogen. My post here explains about lamp spacings and why output between 0 and 20 degrees is the most important. Of the other two the Phillips is arguably 30 – 40 % better than the Kosnic but at 100% more expensive the Kosnic is probably better value.

GU10 LED lamps v 50w GU10 halogen test

LED v halogen, are GU10 LED lamps any good? Here we test two LED GU10 lamps against a standard 50w GU10 halogen. The results are quite suprising.

Lamps tested

Phillips Essential 50w GU10 240v 40degree halogen aluminium reflector

Megaman LR1206dDGv2-WFL 6w dimmable LED 4000K cool white 35degree 410lumen

Kosnic KLED05PWR/GU10 5w LED 4000K cool white 36degree 320lumens

Readings Lux

Lamp 0 degrees 20 degrees 30 degrees
Phillips Halogen 180 219 58
Megaman LED 186 52 37
Kosnic LED 236 42 9
Both the Megaman and Kosnic lamps perform very well when measured directly below the lamp. However, there was a dramatic difference with both at a 20 degree beam angle with the Megaman performing best, but still less than 25% of the output of the halogen lamp. At 30 degrees the output of the Phillips lamp drops considerably, the Megaman gets to within 60% but the performance of the Kosnic is poor.
These lamps would make excellent replacements for a halogen used as an accent lighting source, for example in a spot light. I don’t think I could recommend either of these lamps as a direct replacement for a 50w GU10 in a downlighter. The performance of the Kosnic was especially disappointing when considering it claims on the packaging to be an equivilent for a 50w. If either of these lamps were to be employed as replacements for existing 50 watts in downlighters you would need more of them at much closer spacing to achieve a similar light level.



LED Lamp Test Lab

Here is a drawing showing the lighting test rig, this is what I use to carry out LED lamp tests.



I have tried to recreate a typical lighting situation. The lamps or light fittings are mounted at 2.15M from the floor. (This is a bit lower than a standard ceiling which is usually about 2.4M, but allows space to install and remove the testing equipment). My readings are taken on a working plane 1.4M below the light source. This would be typical of the height of a desk or seated reading position.

Readings are taken directly below the lamp, then at various distances away from this position, at a 20 degree angle from the vertical and a 30 degree angel from vertical.

A simple lightmeter is used to record the light levels in lux. I use a Martindale LM90. For more information on lux and light output see my posts on lumens per watt, candella and lux and LED light output




LED Lamp Replacement Buying Guide

LED Lamp Replacement Buying Guide – How to buy and what to look out for

In a large house converting every lamp to LED will be a similar cost to purchasing a new widescreen TV, considerably more in a commercial premises  The lamps could, indeed should last for 10 years or more so it’s a different type of purchase from a traditional consumable light bulb that may be with you for just a few months and cost pennies. You will very quickly get your investment back of course. My post Energy saving Led lighting, how much can you save? will give you an idea of pay back.

You get what you pay for. All lamps are not equal. Check the rated life and the guarantee. You should expect a life of 25,000 hours or more and light output of in excess of 45 lumens per watt. A 3 year guarantee should be the minimum.

Know who you’re buying from, check out the manufacturer of the product. The overriding factor in the purchase of any lighting product is its light output performance. Be cautious of vauge statements or if no data at all is provided. Look at the leading lighting manufacturer’s products (the likes of Osram, Toshiba & Phillips) and use these as a yardstick for comparison.

The usual rules of any purchase apply. Keep a record of your purchase and the receipt. I have a small permanent black marker that I write on the lamp or fitting when it was installed. Consider the benefits of paying a little more for a well known brand. You can get some reassurance from being able to approach the manufacturer if you have a problem as well as the supplier you originally bought it from. In my experience manufacturers have been very good at dealing with any issues I’ve had. (please comment if you have good or bad experiences).

Most importantly of all make sure you’re getting a light output close to the lamp you are replacing. Less so now, but there have been many LED products marketed as equivalents that are no where near the performance of the lamp they claim to replace. My post on LED light output and lumens per watt, candella and lux explain how to interpret the commonly used figures. There is also a list here of GU10 LED lamps manufacturers performance figures listed alongside data of the lamp they are to replace.

Before you replace lamps or install new fittings in a whole area consider trying 2 or 3 first as a test area. You may be surprised that the light distribution is different. Also, make sure you’re happy with the colour and most importantly (again) that the light level is sufficient.

Be aware that the colour of the light may be different from what you’re used to. See my post here which looks at the difference between cool white and warm white LED lighting.

Cool White or Warm White LED Lighting

Cool White or Warm White LED lamp colour, why it’s important and why you should consider “cooler” colours

Visible light can be many different colours, red, green, violet and so on. White light also has shades within it, indeed daylight has significant variations. The physics of the colour of light is a subject on its own, if you’re having difficulty getting off to sleep one night you can read the wiki article here. We grade the colour of light using a measure called correlated colour temperature (CCT) and assign various gradients with a colour in Kelvin (K). Here’s a chart.


Now here’s a key point, Incandescent (old fashioned light bulbs) and Halogen (GU10 etc.) lamps emit light at a fixed temperature range around 2700K. So toward the left of our chart and it’s a yellowish light. You can’t easily change this so we’ve become used to electric lights producing a warm yellowish light.

Yellow is described as a warm light as opposed to blueish light (at the right end of the chart) that we describe as cold. Even though the hotter you go in Kelvin the Colder the light colour. Confused yet? Just think 3000K = yellow light, 4000K + = bluer light. But it’s all white.

Using flourcescent and LED technology it is possible to control and vary the colour of the light produced. Traditionally flourescent tubes have been produce in 2700K, 3000k, 4000K and 6500K colours, and LED lamps have followed suit.

The main thing you need to know is that LEDs producing cooler colours (4000K plus) are more efficient, and therefore produce more light (lumens). So if you go for a cooler coloured lamp you will get more light for your money.

Some people are very fussy and say things like “I don’t like that harsh white light, I’ve got to have the warm white”. I’ve also seen different coloured lamps being recommend depending on what the room is used for. My own view having experimented with various colours of both fluorescent and LED lamps over the years is that most of the issues with light colour are in the mind. It’s just what people have become accustomed to and they don’t like change. For me the ideal colour is 4000K or even higher as it’s the nearest to natural daylight.

There is in fact a growing view that higher colour temperature lamps can improve the living environment and be of benefit to human health. Conditions such as SAD have been linked with poor artificial lighting.



LED Light Output

LED Light Output – Why It’s Not All About Watts And Why You Need To Know About Lumens

When you buy an LED lamp (light bulb) or light fitting one consideration over rides all others, how much light is going to give out? That is after all the reason you’re buying the thing.

Back in the old days when we only had a single technology for each light source this was a simple matter of knowing the wattage of the lamp (this is the amount of power the lamp consumes).

All light “bulbs” were incandescent and all tubes were fluorescent. So if we knew the power consumed by say a candle lamp we could compare it with power consumed by a standard “100w bulb” and, because they work off the same technology, we can make a rough judgement about how much light we’d get. Same for a 2ft 18w florescent tube in comparison with an 8ft 125w tube. Everyone was happy and knew where they were.

The problems started when we began to mix up the technologies. All of a sudden we were trying to compare a “100w bulb” with a fluorescent product that did the same job, or a 60w incandescent with a 50w halogen. The reason of course is that light is not measured in wattage ( the wattage is the power the lamp consumes, very different to what we get out). Light is measured in lumens.

Okay, so that should be simple then, let’s just start telling everyone how many lumens our lamp produces and everyone will know where they are. Well, that will certainly help but there’s still a problem. Oh, what’s that? I here you ask. The problem is that you can have a lamp that throws out a lot of lumens in an inefficient way. Let me give you a quick example: You are sitting at home reading the newspaper or surfing the web, the lighting in the room is just right (neither too bright nor too dark). The critical light level in this scenario is how many lumens there are on the surface of what you are reading. This is very different from how many lumens are present at the front of lamp on the ceiling.

Where we have lamps (like the old fashioned “100w bulb”) that are non directional and may be covered by a shade or go into a light fitting with some sort of a directional device like a reflector or cowl this is less of a problem. But, when we look at lamps that have built in reflectors it becomes very important.

When we try to compare directional lamps we need to use other units of measurement, candella and lux. I talk about these in a separate post lumens per watt, candella and lux.

Lumens Per Watt, Candella and Lux

What you need to know about lumens per watt, candella and lux when selecting LED lamps

As I explained in my post about LED light output, we have to take care when selecting and comparing directional lamps, that is lamps that have an in built reflector, such as GU10s.

The lumens of a lamp tell you how much light it produces, but when we look at directional lamps we need to know how much light will be cast onto the working plane. If we are reading a book, for example, it’s the amount of light on the page that matters not how much is coming out of the lamp.

To help us measure this we need to know about two units of measurement, candella and lux.

Starting with candella, this is a measure of the intensity of light at a given point. It’s useful because you can have two lamps both with same lumen output that disperse the light differently and so give different readings of candella.

The best lamps are the ones that focus the intensity of light in the areas where it will be of most use. But be careful, simply narrowing the beam of a lamp will greatly increase the candella. So when you compare candella make sure the beam angel is appropriate and the same. Candella is a favourite item of data for lamp manufacturers to provide but in my opinion it is not nearly as useful as lux.

Lux is the measure of light at a given point, so in our example earlier of you at home reading, we could measure the level of light falling on the surface of your reading material and we would do it in lux. Lux is related to our friend lumens in that it is define as the numbers of lumens per square meter at a given point.

So after all that we could say lux is the best way to determine the effectiveness of a given lamp so why don’t we use that. Well, a problem exists because the lux will change depending on where you measure it relative to the lamp. I think the argument goes that if you don’t know how and where the lamp is going to mounted it’s unhelpful to give out data based on that. Certain manufacturers provide data along the lines of this lamp produces x lux at 2 meters (a mention to Kosnic for being very good at this). Personally I wish they all would because it then tells you all you need to know. Unfortunately it appears that we’re stuck with lumens that tell us only part of what we need to know.

I have produced a comparison table that compares Gu10 LED lamps from a number of manufacturers and the data they provide including lux at 2 meters for those who measure it.

Energy Saving LED Lighting How Much Can You Save?

How much could an average household save by changing to energy saving LED lighting?


So you’ve heard about LED, maybe even bought one or two for use at home or work, but do you know if they’re really worth it? Well I’m going to take a look at an imaginary dwelling and see exactly what the savings and return on an investment in energy saving LED lighting would be.

.Let’s imagine we have a modest three bedroomed semi. It could just as well be a large detached property or commercial premises, simply scale up the results. From the table below you will see we have listed the rooms and the existing lighting used. I have assumed that at present all the lamps are a mixture of incandescent, halogen and compact fluorescent. I guess this is typical of most homes in the UK, but the exact mix is difficult to estimate.


The “piece of string” (how long do you want to make it) in this calculation is the amount of time the lighting is used. I have invented a family of 4 who are all out for most of day and children who occupy their bedrooms for a good deal of the evening (probably teenagers). The figures would be very different if our family had a stay at home Mum or was occupied by a home worker. I guess there’s no such thing as typical but I think this serves as a reasonable model.


Kitchen / Diner 50w GU10 12 50 600 2280 1368
60w GLS 3 60 180 2280 410
Dining Room 50w GU10 9 50 450 960 432
Lounge 15w CFL 4 15 60 1680 101
Hall, Stairs & Landing 60w GLS 3 60 180 2280 410
Bathroom 35w MR16 12v 4 35 140 740 104
Bedroom 1 60w GLS 1 60 60 740 44
25w Candle 2 25 80 740 59
Bedroom 2 50w GU10 4 50 200 1460 292
Bedroom 3 15w CFL 1 15 15 1460 22
Ensuite 35w MR16 12v 3 35 105 740 78
Utility 15w CFL 2 15 30 370 11
Garage 58w 5ft tube 1 58 58 100 6
External1 300w T/H Flood 1 300 300 100 30
60w Lantern 1 60 60 1100 66
Total Annual Usage 3433 Kwh

We find that we have an annual lighting energy useage of 3,433 Kw hours which at around .11p per Kwh is an annual spend of £377 (The Energy Saving Trust quote a figure of 15.32p / Kwhr, but I think that’s a bit high, I pay nearer .11p so will use that). Now let’s take a look at our costs if we change every lamp for an LED equivilent.

Kitchen / Diner 6w 400lm 36D 4000K 12 £12.00 £144 72 2280 164
8w 630lm 4000K 3 £18.80 £56 24 2280 55
Dining Room 5w 400lm 36D 4000K 9 £12.00 £108 45 960 43
Lounge 8w 630lm 4000K 4 £18.80 £75 32 1680 54
Hall, Stairs & Landing 8w 630lm 4000K 3 £18.80 £56 24 2280 55
Bathroom 6w 330lm 4000K 4 £12.00 £48 24 740 18
Bedroom 1 8w 630lm 4000K 1 £18.80 £19 8 740 6
4w 240lm 4000K 2 £12.20 £24 8 740 6
Bedroom 2 5w 400lm 36D 4000K 4 £12.00 £48 20 1460 29
Bedroom 3 8w 630lm 4000K 1 £18.80 £19 8 1460 12
Ensuite 6w 330lm 4000K 3 £12.00 £36 18 740 13
Utility 8w 630lm 4000K 2 £18.80 £38 16 370 6
Garage no change 1 58 100 6
External 10w Floodlight 4000K 1 £30.00 £30 10 100 1
8w 630lm 4000K 1 £18.80 £19 8 1100 9
Totals £720 477 Kwh

With the new lighting we use 477 KWh which, at .11p / Kwh is £57 so a saving of £320 or 85%.

The lamps would have cost around £720 including VAT. (cheaper for commercial users who can claim VAT back, and indeed put the capital cost against tax. Perhaps energy saving lamps should be free of VAT Mr Osborne?)


We would get our £720 back in just a whisker over 2 years and from then on save a lovely 320 quid a year. So an annual return on investment of over 44%, not bad! (try getting that at your local Barclays).


I have produced two spread sheets you can download here energy survey and energy saving calculator. If anyone did want to survey their own house, work, club etc. a bit of the work is already done. You can see an equivalent chart here if you need to identify replacement lamps or fittings.


LED or Halogen Lighting?

LED or Halogen – Why LED is so much better than traditional halogen or incandescent lighting?

Let’s have a look at a comparison with old fashioned incandescent bulbs and more modern halogen GU10 or MR16 lamps.

LED has all of the advantages of traditional lamps. You get instant light when you turn on the switch and full light output straight away.

LED is on average around 8-10 times more efficient.

LED will last up to 30 times longer.

Light from an LED source is not hot so LEDs can be used in situations where incandescents and halogens are unsuitable.

LED can be purchased in specific colour temperatures to better simulate real daylight or natural light.

LEDs are very much more robust with no delicate glass and fragile filaments. Drop an old fashioned light bulb and it’s likely you’ve done some damage, where as LED lamps will withstand most typical accidental impacts.

LEDs can be switched frequently with no ill effects. Halogens and incandescent lamps suffer wear each time they are energised and regular switching will shorten their life.

And disadvantages?

Non really, if you wanted to be really picky you could say traditional lamps are better for dimming. Whilst you can dim LEDs, dimmable lamps are more expensive and you may need a special dimmer.

It is worth noting that some of the earlier LED lamps did not live up to the manufacturers claims on equivalence and light output (see GU10 LED lamp comparison table) but now there are many replacements that get close to being like for like.

Finally it is worth considering two other factors we sometimes forget about disposable products. Firstly the energy involved in production, you have to produce 10 halogen lamps for each LED. And in volume terms you create 10 times as much waste when the products life is over.