Some (currently unsorted) pics of my LED lamps
LED lighting is usually done in what I consider to be a very poorly-engineered way. I have written many posts about this in various places, and have finally got round to collecting my thoughts and details of my efforts to do it properly on this page. This should save writing the same rant over and over - I can just point people at this page.
The standard LED lamp in the UK currently is the MR16 or GU10 downlighter as a direct halogen replacement. This is convenient if you already have a load of these fittings, although often you will still need to change the driver unit because it won't be able to drive the factor-of-10 lower power LED you have just replaced the Halogens with. However these are pretty-much the worst form-factor you could choose for LED lamps because the bulb is designed to be kept hot (that's good for halogens), and heat is the enemy of LEDs - it makes them fade and die quickly. So sticking them in a tiny housing, in a hole in the ceiling to collect heat, often with no ventilation, is really bad for them.
Downlighters-in-the-ceiling are bad for other reasons in energy-efficient homes too. They make holes in the ceiling which breaks airtightness and also can allow a lot of water vapour into the loft (e.g. from a bathroom). It also has fire-reg implications and you _should_ have an intumescent cover over each fitting. Now, despite all those caveats, because halogens are barely any more efficient than incandescents at room-lighting power levels, it's clearly a great idea to replace them with LEDs using 1/10th the power. My point is that if you are doing any new-build this type of lighting should be avoided, and even for refurb there are much better ways to do LED lighting.
The other thing that annoys me about LED lights is that nearly all are sold as being '12V' and driven with 12V constant-voltage supplies, or 240V AC with a little (usually cheap and nasty) switch mode PSU in the back of the lamp to generate the (typically) 700mA, 3.6V to drive the LEDs. This is daft: LEDs are current-controlled devices and so to drive them with 12V supplies needs either a series resistor or a switch-mode supply to generate the correct current. Both of these waste power for no good reason, sometimes an embarassingly large fraction of it. Driving them with mains directly needs a switch-mode converter in every lamp.
If you just connect bare LEDs in series to a suitable constant current supply then no power is wasted at all, and everything is dimmable without having to spend on anything extra because LEDs are instrinsically dimmable by controlling the current level. The only reason you have to pay extra for 'dimmable' LEDs is because some idiot put voltage-to-current conversion electrionics in the way in order that they could be run by a '12V' or '240V' supply. It's all nuts.
So I've explained above why I don't like 'LEDs in holes'. The right way to do it is LEDs mounted on aluminium plates or housings to act as heat-sinks. There are a hundred and one ways to actually do this, which could look like designer lighting, or discreet glowing panels, or strips, or little lamps.
One thing I do think is a good idea is to have a quite a few smaller lamps, rather than one huge one. One big one in the middle is like a pendant lamp. Straightforward, but boring and often with unhelpful shadows. LEDs make it easy to have a lot of little ones, and a smaller lamp is easier to heat-sink. Sadly the people who make lamps first just try to sell you MR16s, or if you insist on surface-mount lamps they want to sell you very powerful 17W and 30W lamps. That is an awful lot of light in a domestic setting. A selection of 1-3W (70-400 lumens) is much more versatile.
There is an enormous number of ways of lighting a room with LEDs. Two which I find sensible, paractical and not unreasonably expensive are:
In both cases I reckon it is best to use one CC supply per switched segment. You could use a large whole-house supply but that would be on all the time so would need to have very low standby losses. It would also need to be sized for all the lights in the house, which would hardly ever all be on at once, so it will always be run at the low end of its output range, which is rarely efficient.
You could switch on the LV DC side of the PSU but now you need high-current DC switches to avoid spark erosion, and you will have standby losses because the PSU will be energised all the time. Much better to switch the AC side of the supply with standard wiring and switches, then the supply is only energised when in use. If you want to do dimming, get a supply which is dimmable rather than use some other item to do the dimming. I have not yet done this myself as I'm not much into dimmable lights.
A typical 3x3m sitting room can be lit with one 100W or 150W incadescent bulb, or 4 30W halogens or one 20W CFL. Those are all in the 900-1200 lumens range of total light. To get that from power LEDs you want to find ones around 90lm/W or better and have about 10W of power. So 4 or 5 3W LEDs would do it.
Typcial 700mA or 350mA CC drivers will run 2-5 or 3-8 3W LEDs which is ideal for average-sized rooms. Use two for a large room.
One thing about bare power LEDs is that they are a very bright point source that you don't really want to look at directly (like most other lamps). A frosted cover is the simple solution to this, which just takes the glare off. You do lose some optical efficiency, but I'm not sure how much.
I haven't implemented any of this yet, except to install a few 6W LED strips (which are labelled '12V' but seem equally happy with 12V or 600mA). The trick for a room is to get the right lumens/m so that an even strip all round the edge will provide a sensible light level.
It is quite hard to find strips which are a) efficient, b) the right lm/m (I reckon about 120lm/m). Most strips are either decorative, with very low light output, and often shockingly poor efficiencies, or very high-power where a bit 1m long will light the whole damn room up.
I have found a few strips which look like they might do the job. I have not found any designed to be directly current-controlled, which is annoying. Further investigation is needed, as it is with which mounting methods will work best.
I will come back to this subject soon
So, having decided that I want bare power LEDs mounted on a heatsink, I just have to buy some. Guess what? No-one seems to sell such a simple thing. There are thousands of LED lamps and fittings out there, but I really struggled to find what I wanted. There are very nicely-engineered LED lamps for £100 each(!), and nice surface mount panels with huge wattages, inefficient LEDs, lots of '12V' LEDs, nice designer lights (all expensive), but just about no simple 'LED on a heatsink, with a cover, and no electronics', So I decided to make my own. It's cheap, fairly easy and I get what I want. It would be nice if someone would save me the trouble though; there is a market opportunity here.
The wooklight is very simple. An Aluminium plate about 10cmx10cm with a star LED attached and two wires coming out the back. A frosted acrylic sheet of the same size is put over the front, mounted on 6mm standoffs, to de-glare the LED. You can skip that bit if you won't end up looking at them (I have two in the kitchen without front plates and it's fine).
LED colour temperature, hue, and CRI (colour rendering index) vary a lot, as does whether people prefer the blueish 'cool white' or yellowish 'warm white'. In-between 'neutral white' is sometimes offered too. Buy a few LEDs to see which ones you like before getting a pile. The coolwhite ones are generally much more efficient than the warm white ones (up to nearly twice as good). I prefer the cool white colour anyway so it's easy to pick the most efficient ones. If you like warm white you have to tradoff efficiency against colour temp. The very latest super-efficient LED can also be quite expensive at around €8 each. Slightly less state-of-the-art can be a lot cheaper (€2.5)
These are simple to make if you have tools to cut, drill and solder (jigsaw, file, 2.5, 3, 5mm hss drill bits). You'll also need thermal paste and an M3 tap to have flush mounting (or have nuts on the back).
Once you've got the hang of it it's much more efficient to make these in batches. Getting the ali and acryliuc pre-cut is probably a good plan too. It's not hard to cut but it is hard to cut square and consistently sized.
I used clear acrylic and sanded it to get frosted effect. Apraently you can get frosting spray too.
All sorts of variations on this are possible. You can use unthreaded star-mounting holes and just have nuts on the back. You can use pan-head or CSK machines screws throughout again at expense of front and back not being flush. You could use nylon standoffs and/or front screws (less shadow). You can glue the LEDs with thermally-conductive glue instead of screw them down - then they don't have to be star-mounted and cheaper ceramic-mounted ones can be used. This has worked for me too.
You can also vary the shape of the luminaire and put more than one LED in. I decided that one LED per luminaire was good because you get more flexibility about where to fit them and thus more even lighting. Too many on one luminaire and the room is lit, but all from a central point, giving shadows when standing away from the room centre.
For some FAT star LEDs 6mm standaoffs are not quite enough - use 10mm ones - it really doesn;t matter much.