GU10 LED

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Traditionally halogen GU10 bulbs came in 3 standard wattages: 20W, 30W and 50W; whilst the LED alternatives typically vary from 3W - 6W. It doesn’t need a mathematics degree to see that the LEDs are using roughly 10% of the electricity of the bulbs they are replacing.

The lighting industry assumes an average light bulb is used for 1000 hours a year, so a 10W bulb will use 10,000Whour in a year, or 10kWh/yr, a 20W bulb will use double this, 20kWh and a 50W bulb 50kWh.

Of course not all light bulbs are used for 1000hrs/yr, some are likely to be used much more such as those in hallways, landings and kitchens. Just the places where GU10s are most likely to have been installed in UK homes.

Electricity is usually priced in terms of pence per kWh (or c per kWh if in the €-zone). Assuming a typical domestic price of 15.5p/kWh then a standard 50W GU10 halogen bulb will cost £7.75/year (€9.30) in electricity costs.

In addition most halogens have a rated life of 1000 hours, with better quality branded products rated at 2000 hours. So in addition to the electricity running costs consumers should budget to replace their GU10 halogens roughly once per year at a cost of say £1.50 per bulb.

Adding the running costs to the replacement cost gives a total of around £9.25 (€11.10) per year per 50W halogen. And this assumes just 1000 hours/year usage. Lights in kitchens, hallways etc. may be on for many more hours.

A quick look at the products listed for sale on this page shows that the vast majority cost less than £9 each and they come with a two year replacement warranty - so most customers are guaranteed to recover their investment, up to twice over within the warranty period alone!

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There is considerable confusion about the lifespan of GU10 and other LED bulbs with manufacturers and retailers offering confusing information and in some cases credulity stretching claims.

Customers are used to seeing claims of a life of many tens of thousands of hours, but what do these figures actually mean?

An LED is a solid state electronic component (a chip in the jargon). LED stands for Light Emitting Diode. There is not much that can go wrong with the LEDs themselves but they do emit less light energy per unit of current over time, which is to say they lose brightness over time. A very long time.

A very long time indeed.

CREE, a large USA manufacturer of LEDs claim a useful life of 50,000 hours for many of their high power LEDs, which is nearly 6 years of non-stop use. Clearly, CREE (and the other manufacturers of LED chips) haven’t spent 6 years testing their LEDs in order to work out their useful life. Instead they measure the performance in test conditions when subjected to extreme environmental conditions, especially heat, to simulate a longer operating life.

A quoted useful life of 50,000 hours (or some other figure) doesn’t mean that the LED will last only 50,000 hours. It is the estimated time that the LED can be operated before it loses 30% of its original brightness. That’s right, in our example the LED will still produce 70% of its original brightness after nearly 6 years of constant use.

But, and it’s a very big BUT, GU10 LED bulbs consist of many more components than just the LED chips. There are capacitors, resistors, fuses, transformers and other electrical and electronic components in the bulbs in what is known as the driver circuit.

The job of the driver circuit is to convert the domestic voltage AC supply from the lighting circuit (~230V AC in Europe) to a constant voltage or constant current supply across the LEDs. The driver circuit in a GU10 (and all other domestic lamps) has to do this irrespective of which connector is attached to the live supply and which to the neutral or return.

Each of of the components in the driver also has a life expectancy so the actual operating life of a GU10 LED bulb is the time for the first component to fail…

As it happens the lifespans of the components in a GU10 LED are affected by much the same factors as influence the lifespan of GU10 halogens:

  • voltage (levels and fluctuations)
  • heat

and in addition, as with all electronics, the quality of the electrical supply i.e. the amount of noise on the circuit.

There is considerably more that can be said on the life of GU10 LEDs and other LED bulbs and check out our Info and Articles for more if you are interested.

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Much nonsense has been written about the comparative brightness of GU10 LEDs and GU10 halogens. And a few years ago there was much exaggeration of brightness levels by some of the less reputable retailers, many of whom seemed to unquestionably believe the claims of their less reputable suppliers, without it seemed ever getting independent test reports.

As brightness levels and efficiency have increased there is less need to exaggerate and even the cheapest bulbs are likely to offer acceptable levels of brightness to most customers.

A good quality, branded 50W halogen GU10 when new, run at its rated voltage, will deliver 350~400 lumens. Unbranded bulbs are likely to be less bright than this, but still probably over 300 lumens.

A lumen is a raw measure of light emitted, unlike lux which measures the amount of light at a particular point away from the the light source. You may see claimed figures much higher than this, in the order of 750 lumens, but these relate to low voltage DC halogens not the mains voltage AC GU10 bulbs. (Even more confusingly both are technically MR16 lamps but in the UK the mains voltage GU10 variety are known as GU10 LEDs whilst the DC low voltage GX5.3 lamps seem to have become known by the generic MR16 moniker - we go with the flow here at Homewatt with apologies to the specialists reading this).

An average person is incapable of distinguishing levels of brightness that vary gradually by up to 30%. Changing a light bulb is a gradual change in brightness levels and we have found that anything over 300 lumens seems to deliver acceptable brightness for the overwhelming majority of customers and the Astralumen™ range which starts at 400 lumens, a better brightness than most GU10 halogens.

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GU10 halogens and their low voltage siblings were originally conceived as display lighting and produced with narrow beam angles: 10º~15º not being unusual. As they have become widely adopted for general lighting in domestic use, the industry has standardised on a wide flood beam of precisely 38º.

A narrow beam does create pools of light, an effect appreciated by lighting designers and architects but in practice it means that much of the light emitted goes to illuminate the floor, your shoes, or at best a work surface.

GU10 LEDs come in a wide variety of beam angles and we have found that the wider angles make much more sense for general purpose lighting. LEDs by themselves don’t focus their light, but unlike filament bulbs, including halogens, they do emit light directionally.

The beam angle of a GU10 without any lens is described by convention as 120º and we have found this is an ideal beam angle for general purpose lighting. Bulbs with a 120º beam tend to have the LEDs mounted on the face of the bulb or possibly slightly recessed which can create a dazzling light, especially if the ceiling is very low. That said we use this style of bulb at Homewatt Cottage in surface mounted fittings on very low ceilings and we adjusted almost immediately to the effect.

Where the LED is mounted within the bulb casing then the casing itself will create some beam and usually a polycarbonate lens is also present allowing a more tailored beam angle. So for example the Astralumen™ GU10 bulbs have a 60º beam angle which combined with their high brightness means they offer the perfect combination of general purpose lighting whilst still creating enough beam to illuminate worksurfaces brightly or for use in high ceilings.

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Colour temperature for our purposes is usually measured in Kelvin as shown on the chart:

colour temperature chart in Kelvin

Domestic incandescent bulbs, including halogens, have a colour temperature of around 2700K. Which is a soft warm, yellow/orange colour. There is a UK standard (courtesy of the Energy Saving Trust) for describing warm white which specifies a range of colours between 2700K~3500K. There is a noticeable difference in colour and effect between the upper and lower end of this range and we have found that 3500K is often unacceptable for customers looking for a warm white. Our maximum is 3000K for warm white with many such as the Astralumen™ range having a warm white colour of ~2800K.

At Homewatt we offer our GU10 LED bulbs in both warm white and daylight white. We define daylight white as having a colour temperature of around 6400K, which as the chart shows is a white white.

Daylight white bulbs may output very slightly more light but usually the difference is too small to notice. The light is crisper and offers better contrast but it is also colder, making it more suitable for work areas than relaxing.

Our general advice is choose colour above brightness and if in doubt choose warm white. We list the different colours of each bulb separately making it easy to choose.

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Colour Rendering Index is an indication of how a light source (such as a GU10 LED or halogen bulb) shows colours in comparison to a reference source. The reference source being a black body radiator will have a CRI of 100.

Halogen and other incandescent lamps, as black body radiators, have a CRI of 100. A good quality domestic LED such as the Astralumen™ range will have a CRI of 80~90 meaning they render colours similarly to incandescent bulbs.

Lower cost LEDs have lower CRI values.

In reality, although CRI is an objective measure, it is an imperfect guide to how LEDs will work in a particular room. In part this is because it ignores the effect of colour temperature on colour rendering but mainly because LEDs (especially the lower cost chips) have specific peaks in their spectral output which has different effects according to the colours being rendered.

We only use good quality chips from Tier 1 and 2 manufacturers and colour rendering is important to us regardless of the tested CRI value. Our experience is that most customers are happy with the colour rendering from all the varieties of LED we offer but if you have particularly chosen subtle shades of colour and need them to look the same after swapping to GU10 LEDs then we advise spending a little more and buying higher CRI bulbs such as the Astralumen™ range.

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All our GU10 LEDs have an efficacy in excess of 40lm/W and meet the requirements of Part L of the Building Regulations.

There have been instances where building inspectors have questions the use of GU10 fittings as they can be retrofitted with halogens, which do not meet the requirements. Our experience is that fitting with LEDs and explaining the investment cost made (we can provide copy invoices if required) is enough for the inspector to allow the fittings - as after all why would anybody then switch back to halogens?

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All GU10 halogen bulbs come in a standard size of diameter 50mm (Ø50mm) and a length of L55mm. Some old recessed fittings relied on these de facto standard dimensions and fixed the lamp holder to the base of the fitting. This meant that when longer bulbs were used they protruded.

Similarly, some surface mounted fittings have a shroud that hides the lamp holder and is designed to exactly match the edge of the lamp. Again, longer bulbs will protrude.

Diameter is not a problem: all GU10 LED bulbs are Ø50mm.

For the vast majority of modern recessed fittings there is no problem. The lamp holder is usually floating inside the fitting or the ceiling void and will accommodate all lengths of lamp. If you have a surface fitting with a shroud it may be worth checking the length of the lamp. Most of our GU10 LEDs are L55mm and will fit exactly; but some, especially the more powerful bulbs, may be 1mm~2mm longer and you will have to decide whether this is acceptable.

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Dimming driver circuits have evolved very quickly over the last few years and it is now possible to buy reliable, long lasting dimmable GU10 LED bulbs that perform every bit as well as their non-dimming equivalents. We also offer a range of dimmer switches especially designed to work with the low loads and internal electronics of LED bulbs.

The two golden rules of dimmable LEDs are:
1. only use LED bulbs sold as dimmable on dimming circuits;
2. Don’t use dimmable LEDs on non-dimming circuits

Breaking either rule risks early life failure of your expensive bulbs and possibly your dimmer switch as well and you may well invalidate your warranty. The second rule is perhaps less crucial than it used to be as the electronics have become more tolerant with evolved designs, but we advise following it.

There are some other things to be aware of with dimmable GU10 LEDs. The dimming range can vary from 0%-100% with some bulbs (and switches) to 30%-100% for others. Ours will dim to 0%, in the case of the Astralumen™ range, or 10% for others when used with suitable dimmer switches.

Be mindful that LEDs will draw 90% less power than the halogens they replace and dimmer switches are designed to work with a minimum and maximum load and additionally should specifically say they are designed to dim LEDs.

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