Choosing which light bulb for which job is no longer a simple affair. With a wall of bulbs to choose from it can be a daunting task. We asked John Butterworth to cut through the hype and shed light on which bulb for which job and what the blurb on the box means.
I could have called this article ‘Low-energy Lighting’, because that’s what we think we’re after, but when you pause for a moment, what we’d really like is the same amount of light we’ve got now, in most cases, but to use less power to produce it.
It’s a crucial difference when you start trying to replace your current lighting, as you’ll all too often find that the Light Emitting Diode (LED) and Compact Fluorescent Lamps (CFLs) very often don’t quite live up to the hype. It’s not that they don’t work, more that they don’t always offer as much light as you were ‘LED’ (ha! ha!) to believe.
When we first came across CFLs, they were sold as the answer, but if you tried using one to light your stairway, you’d find they took so long to reach full brightness that you’d either already fumbled your way along, or fallen downstairs by the time they lit it up. Then there was the ‘dull’ light you got – a sort of sickly white rather than the nice, warm, pale-yellow we’d all got used to from the old-fashioned tungsten filament light bulbs.
LEDs came along, full of Eastern promise (most are made in China), and the light was a jewellery-shop bright white, and equally unacceptable for domestic lighting. Then there was the plethora of fittings, and some worked with dimmers, but most didn’t – so what should you do?
Well, here’s a simple checklist of what to look for, and what’s available now. We’ll look at internal lights here as that’s where most of your lighting energy is likely to be expended. In a nutshell, things are better now, but we’re a long way from lighting Utopia yet.
Remember, it’s how much light you get for your money that’s important, and we measure that in ‘lumens per watt’, as you’ll see. If you get 10 lumens per watt from a filament lamp, but 100 from an LED, the LED uses one-tenth of the electricity, so costs one-tenth of the price to run.
THE DIFFERENT TYPES OF LIGHTBULB
With domestic bulbs (or lamps – it means the same thing), we’ve been used to buying 40W, 60W and 100W bulbs, and knowing fairly accurately how much light we’d get. These were ‘tungsten filament’ lamps, where tungsten was the metal used as the element that lit up when power (and the ‘watt’ is our measure of power) passed through it. The trouble was, and is, that more than 90% of the electricity was used to create heat, and less than 10% turned into light – in other words, they are very inefficient, and a colossal waste of electricity when you think how many lamps we jointly have, and that’s the reason that they are now banned from sale in the EU.
Halogen lamps are a bit of a stopgap between the tungsten filament and the much lower power CFL and LED lamps. They use less power, but not a lot less, for the same output – for example, a 40W tungsten spotlight can be replaced with a 28W halogen, and still be as bright. The power savings quoted are ‘up to 30%’. Here’s what’s inside the outer glass case when you accidentally drop one on the floor and break it.
Inside a halogen bulb
There’s still a tungsten element inside, but it’s encased in a tough little glass envelope filled with halogen gas under high pressure. The gas doesn’t glow like in the CFL (below), but it allows the element to run more efficiently at a higher temperature and give off more light, without burning out.
The CFL (see main feature picture) is a lot more efficient in converting power to light than the lamps with elements; electrical current is passed through a gas in a glass tube, mostly argon gas with a dash of mercury vapour, and this generates ultraviolet (UV) light. We can’t see UV, but the inside of the glass tube is coated with phosphor, and UV makes phosphor glow with visible light.
Screw-in CFL in a wall fitting
They use about 75% less energy than tungsten filament lamps. There’s an electronic circuit inside called a ‘ballast’, which kick-starts the process, and there’s a time of between 30 seconds and a few minutes for the whole thing to settle down and become stable. That’s why they appear to take a while to warm up to full brightness.
LED spotlights
LEDs are very different again. There’s no gas involved, and no element; the light comes from an electronic ‘junction’ between two types of material in a device called a diode (a sort of electronic one-way valve). When current is passed through the junction, it gives off light. Early ones were all red (remember those cool LED watches?), but further development came up with a range of colours – blue was tricky, but now they’ve managed it, so our fairy lights were suddenly blue in 2013. There is no white LED, but a range of colours can be added together to illuminate a yellowish-looking phosphor coat, which in turn gives off a white light. These are slightly more efficient than CFLs, but not much more – as yet.
Here’s a table showing typical replacement bulbs for your current tungsten filament or halogen bulbs, both of which are being phased out by the EU. If I couldn’t find a replacement, there’s a question mark.
Filament Bulb
Halogen Bulb
LED
CFL
LUMENS (typical quotes)
?
500W
?
?
8500
?
300W
30W
65W
5100
100W
80W
?
23W
1300–1600
60W
45W
12W
12W
720–800
40W
30W
8W
8W
420–450
COLOUR OF LIGHT
Here’s an important thing to look out for – what’s the colour of the resultant light? We’re used to the slightly yellowish light of filament lamps and tend to dislike the whiter light from fluorescent tubes, possibly because it reminds us of school, but maybe that’s just me.
Manufacturers have finally reacted to this, and now advertise a range of ‘colours of white’. The kelvin scale of temperature is used to define this colour range – for a ‘warm white’ like tungsten bulbs, look for 2700–3000K; for a ‘cooler light’ (sort of ‘hospital corridor’) 3500–4100K, and for a blue-white (‘jeweller’s display cabinet’!) 5000–6500K.
FITTINGS
Here’s a common range of interior lamp bases – there are many more. On the left is the commonest, the ‘bayonet cap’ or BC. Next is the ‘Edison Screw’ or ES, referred to as an ‘E27’, as it’s 27mm in diameter. In the centre is the ‘Small Edison Screw’, SES, or E14, as it’s 14mm in diameter. Second right is an ‘MR16’ or GU5.3 (5.3mm) spotlight, and on the right a GU10 (10mm, of course) spotlight. The last two are typically LED or halogen lamps.
TRANSFORMERS AND DIMMERS
Most lamps in domestic premises tend to be 240V a.c. – the mains voltage. Some fittings are 12V a.c.; the ‘track-type’ spotlights like these virtually always are, because they’re safer: the track can be ‘live’ to slide the lamps to different positions without killing the householder – always an advantage. One downside is that there is often a visible transformer, like this one, to transform the voltage from 240V to 12V. The other is that they can’t be dimmed from the normal light switch, as that’s switching 240V.
Likewise, most CFLs are not dimmable, which may be a major downside for you. I’ve got round it by having one wall fitting in the living room switched separately, with a CFC, and the others on a dimmer switch with halogen lamps in them.
If you have tungsten filament bulbs on a dimmer switch, the chances are it’s a ‘leading edge’ dimmer, as they are cheaper to produce. It won’t work with 240V LEDs, so will have to be changed for a ‘trailing edge’ dimmer, and here’s what’s inside one.
Inside a dimmer switch
It’s a very simple job to replace an on–off switch with a dimmer switch, or an old-fashioned dimmer with a new trailing edge dimmer, but if you are in any doubt, get an electrician. This dimmer works with halogen and filament bulbs too, by the way.
POWER AND LUMENS
Watts are a measure of power, and the watt-hour, or more commonly the kilowatt-hour, is a measure of energy, that is, the power used over time. When a low-energy lamp said on the box ‘equivalent to a 60W bulb’ (or 100W, 40W, etc.), the manufacturer was mixing up his units: not to confuse us punters, but because we’d got used to judging roughly how bright a 40W, 60W or 100W tungsten filament bulb would look in our living rooms.
It worked at first, but once people had already changed to halogen, or CFL or LED bulbs, it became pretty useless. There is a measure of light though, the lumen, which is a lot more useful, as it works for any type of bulb. For example, a bulb that gives off 500 lumens is exactly as bright, whether it’s tungsten, halogen, fluorescent or LED.
Here’s a little table giving the equivalents. The numbers are not fixed, as the low-energy bulbs are getting better as new developments come on the market, so if last year a 22W LED bulb gave off 1600 lumens, the 2014 model is likely to be more efficient, and maybe needs only 20 watts to give off 1600 lumens.
Type of Lamp
Lumens per Watt (typical claims)
Tungsten Filament
10–15
LED
70–100
CFL
50–80
Halogen
8–17
Sodium
85–200
There is a theoretical limit though – a 100% efficient LED could produce 683 lumens per watt, and they’ll never reach 100% efficiency. Also, the quality of light that we demand – called ‘polychromatic’ light, i.e. multiple wavelengths that make up ‘warm white’ – has the theoretical limit of about 250–300 lumens per watt. To nitpick further, we have to talk about ‘efficacy’ rather than efficiency – see Further Info.
Regarding COST: if a 100W bulb runs for 100 hours, that’s 10 kilowatt-hours, which costs about £1.50. If you could get the same light using a 10W LED, it’s 1 kilowatt-hour, so only costs about 15p.
AND FINALLY…
What manufacturers claim and what you get don’t always tally (who’d have thought it!), so the tables don’t quite line up with each other, or reality. LEDs are improving fast, but still have a way to go; the dimmable spots, for example, are still pretty awful in my experience, so I’ll wait before I replace my halogens in the kitchen. CFLs have improved, so they come up to full brightness much faster now, and as regards ‘light per watt’, hence, how cheap they are to run, there’s not much to choose between a CFL and an LED, yet.
Don’t pay a lot for a ‘super-efficient’ bulb just yet; wait until the price comes down. I’ve seen some LED lamps priced at £30+; that price will drop soon.
Often the box says ‘replaces a 40W filament lamp’, but the lamp is simply not as bright, for example a 28W halogen. So in truth, it’s not a direct replacement – beware.
For outbuildings and yards, the old fluorescent strip lights and sodium lights still compare favourably with newer stuff, so if you have them, I’d stick with them!
Further Info
* Lumens vs watts explained: http://www.carbonlighthouse.com/2014/02/13/683-lumens-per-watt/
* Trailing edge dimmers – I got mine from myswitchshop2011 on eBay. It’s a Varilight 1 Gang and cost £13.85. It’s highly recommended.
* The ‘snubber’ is a 0.47 uF 100 ohm AMPOHM from Amazon and costs £7.59.
* 30W LED floodlights for your yard/drive are about £25 on eBay, or just over £30 with a built-in PIR.
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