Difference between revisions of "Halogen Lighting"
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Revision as of 13:49, 4 May 2007
A halogen lamp is a type of filament lamp with slightly higher efficacy than standard GLS filament lamps. Halogen lighting is popular but suffers a number of drawbacks compared to other types of lighting.
To those who have not heard of the various issues before, the sheer number of issues may come as a surprise.
Halogen capsules run extremely hot. Contact with paper or plastic quickly causes ignition.
- This is not a problem with downlighters using reflector lamps, as these have lower surface temps and gravity normally keeps flammables away.
- However it is a serious shortcoming of halogen uplighters.
Halogen downlighters are usually mounted in holes in the ceiling. They pierce the plasterboard fire & smoke barrier, permitting quicker spread of fire and lethal smoke in house fires.
Approx 500 people die in house fires per year. 40,000 will die in house fires in one 80 year lifetime. How many of those would have survived if not for a compromised ceiling fire & smoke break I have no idea. I guess it would be a large number of fire deaths multiplied by small odds, but what number this comes out to I don't know.
So installing halogen downlighting is a small risk to life for you and your family.
The solution to this problem is intumescent fire hoods. These are floppy hoods that fit over the light fitting, and in a fire they will swell up and block the hole. However they are usually not fitted, and they're not much help when you don't have them.
Upturned clay flowerpots are also occasionally found used as fire hoods.
Of all the filament bulb technologies commonly in use, halogen bulbs are amoung the most efficent. With low voltage halogens being better than mains voltage ones. However it has to be remembered that the energy efficiency of any filament lamp will be poor compared to alternative technologies if all you are interested in is the most light per watt of power consumed.
Careful choice of light fittings will make a big difference to the overall practical and energy efficiency of the lighting. For example, attempting to cover large floor areas using nothing but downlighters will not only prove to be an expensive to run solution, but will also tend to give uneven lighting. The use of "wall washer" fittings will tend to give a much more effective and aesthetically pleasing general lighting coverage than downlighters. Using concealed linear fluorescent lighting to provide general background illumination, and then using halogen spotlights for feature lighting or task lighting will often give far more effective and attractive lighting in a room. Note that poor choice of lamp fitting also translates into
- energy & money waste
- higher indoor temperatures
- increased aircon running costs when aircon is used.
Don't worry about the cost of the light fittings, you'll pay 4 figures extra to run them.
2 rooms with 5x 50w halogen bulbs each is 500w of halogen lighting, versus 200w of filament or 50w of CFL.
If these are on 6 hours a day, annual energy run cost = 6*365*0.5*10 = £110 at 10p per unit.
Compare this with GLS at £44 a year, or CFL at £11 a year.
So the extra electricity cost over CFL is £99 a year for just 2 rooms. Per 25 year product life that's £2,475. For 2 rooms only. Light your whole house in halogen and it'll be a fair whack more.
And the extra electricity cost over GLS is £66 a year for just 2 rooms. Per 25 year product life that's £1,650 extra for 2 rooms only. Again, light your whole house in halogen and its more.
Then there's the cost of the bulbs. For 2 rooms with 10 bulbs total, with 1500hr low voltage bulbs @ 75p each thats 6*365*10 = 21,900 hours of bulb operation per year, or 14.6 bulbs. @75p each that's £11. Not much. Over 25 years its £275.
Compare with GLS 1000hr bulbs @ 20p each, 4380 bulb hours = 4.4 bulbs = 88p
Compare with CFL, 4380 bulb hours is apx 1 bulb per year @ apx £2.
Total extra cost of halogens for only 2 rooms over 25 year product life is:
- compared to GLS: £1650 + £274 = an extra £1,900 per 2 rooms.
- compared to CFL: £2475 + £273 = an extra £2,750 per 2 rooms.
The one thing I like least about halogen downlighters is that they make it impossible to lean back comfortably in your own home. Lean back, face upwards, and you're looking into a very intense light source that contains UV. This means pain.
On a lesser level, halogen downlights bouncing off glossy surfaces such as kitcen worktops cause a dimmed reflection of the high intensity light bulb, meaning more discomfort and glare. Bouncing off stainless steel utensiles its worse. Much worse.
Glare impacts visibility. Its harder to see things properly when you've got a high light level shining into your eyes.
Halogen downlighters are spotlights. They need to be, as seeing such an intense bulb in the line of vision would be intolerable.
Spotlights give uneven illumination, halogens more so than most because they're such small light sources. Uneven illumination means dark underlit areas. To make up for this one has to use many lights scattered round the room, and raise the overall lighting level so that the dimmer areas are adequately lit.
The result is uneven illumination, which does not aid clear vision, and over intense illumination, which is wasteful as well as uncomfortable.
Relamping (replacing light bulbs) is a normal inconvenience of any lighting. But halogen downlighters are unusually poor in this respect.
For low voltage halogens, a set of 5x 1500hr (mean life) bulbs means 5 are replaced per 1500 hrs of operation, which is one per 300 hours on average. 3 rooms with 5 in each means a bulb for each 100 hours of use.
Compare this with a single GLS lamp at one per 1000 hours, or CFL at one per (typically) 5,000-8,000 hrs.
Mains voltage halogens have a second problem. As well as needing lots of bulbs they have fragile filaments prone to premature failure. This often increases bulb consumption further.
Note the premature failure problem applies to mains halogen downlighters, but not to low voltage halogens, nor to high power mains halogens (300w,500w). The high relamping rate applies to all multi-bulb halogen lighting installations.
Halogen lamps run at high pressure when hot. Due to high pressure and high temperature, lamp envelopes do occasionally physically fail. Thankfully this isn't too common, but when it occurs you've got lots of pieces of quartz lamp envelope flying out at speed, all hot enough to set fire to things. If you're in the vicinity, you really have a problem.
The solution to this is a toughened glass guard. This prevents fragments of shattered bulb flying out of the fitting.
- Reflector bulbs have this built in, as the outer glass of the bulb is a separate item pre-fitted to the inner halogen capsule. So these are not an explosion risk.
- When using small capsule bulbs, all fittings should have a glass guard fitted.
- For high power linear halogens, often used outdoors, the fitting should always have a glass guard.
- Many fittings that need a glass guard have none. These are a known risk.
Unlike GLS lamps and CFLs, halogen capsules produce ultra violet. UVA, present in ordinary sunlight, is a known carcinogen.
Glass covers filter this out, and halogens require a glass cover for reasons in the section above. However not all fittings have glass covers. Those that don't will produce UV.
The level of UV produced is much lower than that in sunlight, so the risk will be very much lower too. On the other hand sunlight does cause a lot of cases of skin cancer.
When filament bulbs blow they sometimes trip the mcb, taking all the lights out. Mains halogens are worse at this for 3 reasons:
- Halogen lighting uses many more bulbs, which increases the odds of a trip by several times.
- Halogens have higher switch on surge than GLS filament bulbs, which adds to any arc current to give higher odds of the mcb tripping.
- Halogen capsules are small compared to GLS filaments, much increasing the odds of arc-over.
This problem does not apply to 12v halogens, which are normally soft started and current limited by electronic 12v transformers.
One of the advantages of halogen lighting is that it is dimmable and hence highly controllable. It is important to remember however that dimming is an aesthetic measure designed to controll illumination levels, and not is not an energy saving measure. (Dimming filament bulbs reduces can reduce their light output significantly, but this does not translate into an equal reduction in energy consumption. To take an extreme example, A 500w halogen spotlight dimmed such that it produces the same light output as a 40w GLS bulb, can still be consuming 300w).
An alternative way to effect dimming is using a switchbank (i.e. arranging multiple lamps into separately switchable groups such that groups of lamps may be switched on or off to change lighting level). To work well, the lighting layout and the choice of fitting needs to be carefully considered:
- For greeatest control with LV halogen lighting it is more useful to use one transformer per bulb (or one for two) rather than running multiple lamps from a single large transformer. (The extra cost of additional transformers will get saved many times over with a well implemented switchbank design).
- If directional halogen lighting has been used in inappropriate ways, then use of a switchbank may compound the uneven lighting problems.
Even on PIR lights, halogens come up short. The reason this time is not the fault of halogens, in fact halogen is a good choice for PIR use in principle, if not in practice. The problem is simply the popularity of excessively high power fittings. There is simply no reason to use 500w on most properties, doing so just wastes energy and dazzles people, so when the lamp turns off again they're left totally blind for a while. A 100w GLS lamp on the PIR is more sensible for most of us.
Advantages of halogen lighting
For all the limitations of halogen lighting (or any filament technology for that matter) there are many situations where this type of lighting has specific advantages. Careful lighting design can make for very effective "mood" lighting. Wall washers can provide a subtle indirect and diffuse light with more "interest" than the flat blanket illumination provided by big a central light fittings. Combined with dimmer switches, a very restful environment can be created with no direct light sources to catch your eye, and no strong shadows.
The narrow beam width of some halogen spotlights can make for very effective task lighting, directing light just where it is needed without too much overspill. Small halogen reading lights in a bedroom for example, can provide discrete illumination of a book for one person without disturbing another trying to sleep.
Halogen spots are also an effective safety measure for task lights in workshops and machine shops since they can direct bright light where needed to avoid the strobing problems associated with a standard fluorescent room lighting (where the 50Hz flicker produced can result in stop motion effects that may obscure movement of rotating or moving machinery).
LV halogens in particular produce a very white light, that gives good colour rendition. The small source of the light also produces more specular reflections. Hence halogen lighting can be very effective for display lighting, since it will add "sparkle" to ornaments, glassware, and other objet d'art. The use of dichroic lamps and fittings can enhance this effect, while at the same time reducing the heat radiated forward from the bulb, which can be valuable in confined display cases.
If you really want the style of halogen lighting but don't want all the problems, there is one way to do that. That is to use very much lower power downlights, eg 5w instead of 50w, using non-halogen uplighting to provide the bulk of the required lighting. The small downlighting bulbs can be CFL or filament.
Some 3w, 5w, 7w and 9w CFLs will fit into R80 spotlight fittings.
If you really want the filament look, another options is car lightbulbs. These provide various low wattage bulbs that will all run off a standard 12v halogen transformer, and some (eg double ended interior light bulbs) are small enough to be go in surface mounted fittings. You will however need to either take standard fittings and replace the bulbholder or produce your own fittings.
With non-halogen filament bulbs the bulbs are best mounted so the filament is more visible to give the impression of a brighter bulb. A semi-visible 5w filament bulb is a lot more comfortable than a 50w halogen reflector lamp!
Other than all those problems, I'm sure halogen downlighting is a great idea. I just can't think how.