One significant limitation on LED lighting at the moment is power (ie the amount of light produced). As of 2007 I liked my lighting bright, so for example my then desk lamp in my study was a 20W 1200 lumen mains CFL. As of 2009 I'm cutting my suit to fit my cloth, and generally working by a 3W cool-white LED driven by off-grid solar, or go wild and use my 9W warm-white LED. The brightest LED bulb that I had been able to find with any sort of standard fitting circa end of 2007 was a cool white 5W 300 lumen 240V AC mains LED (from ultraleds.co.uk) with a spotlight (screw) cap. (Note: this bulb seems to cause significant interference on a VHF FM radio about 2m away, unlike the CFLs in the same spotlight lighting strip.) We didn't much like it to start with, but in conjunction with warm CFLs, and illuminating our blue countertops, it is growing on us.
Note that although the latest round of off-the-shelf LED technology in 2007 is passing the efficiency of CFL at 60lm/W, the theoretical maximum efficiency of lighting is over ten times this, so we have along way to go still! The batch of LED technology in the labs as of mid-2006 is passing 130lm/W, so we can hope for a doubling of light output for the same input power soon for roughly ten times the efficiency of incandescent! And note that LED lamps have no 'warm-up' time, which even new CFLs exhibit.
LED lights, often as drop-in replacements for miniature halogen display lamps, are becoming widely available in the high-street as well as over the Internet, and are passing the efficiency of the best widespread alternative, so we could be on the cusp of a small but well-lit revolution! The main barriers to household use that remain are cost (around 5x/10x that of CFL) and maximum light output (about that of a 25W incandescent for a 5W LED).
The relative cost of LED compared to CFL is probably not as bad as it looks, because the very long lifetime of LED bulbs may well compensate (at several years of continuous operation for LEDs vs maybe 1 or 2 for CFL).
And maximum power? Osram has developed an LED spotlight with output greater than 1000 lumens at about 75lm/W (March 2007), thus competing well with standard domestic incandescents (~60W) and CFL (~17W) in light output, and significantly more efficient than CFL.
Mains LED Lighting: REVIEWS
I'm trying to test out a wide variety of retail LED lamps for acceptability, power, etc (up to 2009 available Wattage and lumens has been limited per bulb), so see my mini reviews below...
Children's Nightlights
Both our children's nightlights as of 2009 are (0.5W) LED mains socket plug-ins, a tiny 1/10th the consumption of the incandescent type that we used before. Note that they don't actually seem to draw less power when they turn off due to the room being bright, but we turn them off manually anyway.
3W GU10 6000K 'Cool' White as Child's Bedside Light
Our toddler's bedside light is now a 3W mains gooseneck "cool" (6000K) LED directed up at the ceiling as indirect lighting, and works well for her (purchased circa 2008). (It's meant officially to be my soldering/closework desk/work spotlight, but I don't need it most of the time and it works well in this alternate role.) When I was young my bedside light was a 60W incandescent; this is safer and cooler and probably represents a distinct energy saving, and should last a long time. (My daughter is also tester for other GU10/240V lights that cross my path!)
5W ES27 (screw) Spotlight 'Cool' White in Kitchen
We eventually found a good site in our kitchen for the 5W LED "cool" (6000K) spot from UltraLeds.co.uk (which was the highest power available ~2007), and though it is a little weak/watery, it works fine with the blue elements of the decor. (One issue with a light that is going to last many many years and cost lots is that we'll have to think about and plan more carefully what we buy, whereas before we knew we'd be buying a new bulb inside a year anyway, and didn't have much choice in light colour nor CRI/rendering issues.)
2W ES14 (small screw) Candle 'Warm' White as Child's Reading Light
As of the end of January 2010 the 20W halogen lamp that we were reading to younger child by physically broke and was unsafe, so we spent £4 on a small simple bedside E14/ES14 (14mm Edison Screw) lamp and although it won't be on much and we have spare ES14 incandescents I thought I'd see what LED lights were available retail in our local shops. At least two shops had 2W-rated candle-style lights available for ~£9, so I bought the Philips "AccentWhite" warm white from John Lewis. (Actual consumption seems to be 1.6W, with a power factor of ~0.4.) Nothing of a higher rating was (yet) available in that fitting in LED, though 7W/8W CFLs such as the one in my own bedside light are. Nominally it has 20 years' life (20,000h) though I suspect it might outlast me!
LightPlanet EQ60
Preliminary testing of a pre-production 'warm white' EQ60 (in an anglepoise ES27 fitting) is very satisfactory; pleasant solid light, though consumption >7.5W.
More soon, including the Light Planet EQ60 at up to 80lm/W, in a variety of locations, see updates below...
Cautionary Tale from Yesteryear
A real-life story from 2005 as related by a friend:
An electrician I know was working on a huge house in [the UK] and building control wanted to see x percent of low energy lamps as required by law. The owner then decided to replace all the lamps in the house with LED ones. Apparently it looked good.
For me the problem with them is that the light seems bright, but the light that falls on the surface isn't as bright as you think it is. One of the local wholesalers has a demo of various lighting methods, and they have LED downlighters alongside conventional GU10 lamps. The LED looks bright in comparison to GU10, but the light at the source just isn't.
12V DC Solar Power
The reason that I've taken a special interest in LED lighting is because I'm trying to find efficient low-voltage lighting for my solar power PV project, mainly for a decent desk lamp replacement. The initial light for this project was a 16W caravan-style CFL, which is a little bit flickery and blue for my liking, and which produces noticable heat from its built-in inverter. The initial LED lighting that I now supplement this with is a 3W 180° floodlight white LED meant for car 'modding' fancy lighting effects. It is tiny, but mounted behind my shoulder sheds a noticable light that fills in many dark corners and avoids the feeling of sitting in a candle-lit cave!
I'm looking for a 'warm' white LED next, and I have seen lamps rated up to 9W. However, it seems that the warm white is significantly less efficient than the cool white LED format for now, so I'm still looking...
Captain's Log
Update 2007/09/23: I stopped using the 3W LED 'car modding' light as backlighting some time ago, as my warm-white 13W CFL is very comfortable to work by. However, today I noticed that my local lighting shop had in stock on the shelf a 3W white LED MR16 spotlight/lamp and the base to plug it into. I was curious to try the MR16 format, since it seems to be very popular. The light (6000K) quality/colour is OK, though seems to be the same yellow-phosphor-over-blue-LED construction that we don't much like in our kitchen 5W LED spot. This doesn't feel as watery and weak somehow. (November 2009: we rearranged our kitchen lighting a little, and using the 5W LED as a spot for our blue countertops works well.) It does not not seem to provide enough general illumination to work by (ie the lighting angle/cone is very narrow) but in a pinch might do if for some reason I find myself very short of power or the CFL breaks! (On further fiddling to set it up as an indirect uplighter, I think this could just about do as a work light, as I'm using it right now.)
Update 2007/11/07: I have been using the 3W LED MR16 as an uplighter most of the time over the last month or so, particularly later in the evening. Earlier, when the sun has just gone done, I prefer the brighter CFL sometimes. But note that I'm still entirely on solar PV powered lighting, and have not once yet run out of juice!
Update 2008/02/17: I am still mainly using the 3W LED as I have since November, but there are times such as this evening when I go hog wild and use the CFL instead!
Update 2008/08/23: Yesterday I ordered from UltraLEDs one of these warm-white (3500K) 9W 500lm LED dome lamps and added to my RE system. It arrived today: very good service! The dome's light intensity and colour is very close to that of a similar wattage 'warm' (mains) CFL that I have in the same room, and should be a little less depressing to work by on a cold winter's evening than the cool-white... Having both the dome and the spot on at once is pleasing too. The 9W dome light cost £40 (~USD80) whereas a similar-rating CFL might cost 1/10th of that, so the technology is here but the price needs a little work for prime-time...
Update 2010/01/11: Thurmond in Texas very kindly sent me an assortment of power LEDs to play with! The very first thing I did was replace the incandescent bulb in my daughter's 2-cell (NiMH rechargeables) torch with one of the pieces Thurmond provided, and it gives a much brighter (and bluer) light and should proably last longer. Even better, those cells were charged in the summer from our PV I believe... (Just noticed in an ad the EQ60 60W replacement bulbs from Light Planet which is 7W/560lm, which is on a par with CFL if so, and these claim to be the same shape and size as an incandescent and at ~£15 could be a very good deal. I had a chat with Light Planet and I am buying one and borrowing another for eval for this page.)
Update 2010/01/14: The lights turned up today. Although the specs on the box are more modest than described on the phone to me (though this is from a pre-production sample/test batch), the ~7W ES27 (Edison Screw) spotlight is brighter and gives off significantly less heat than the (slightly aged) 12W "softone" CFLs next to it and is a really nice light, and is small (hardly anything will actually physically fit in that socket). If what's on the box is right then it's 7.5W/450lm (Cree LEDs), which is the same efficiency as a typical CFL. The cool/daylight version is 560lm it seems, so ~20% more photons for the buck. The box brand is 'tess' (from Taiwan), part T-67004, 200V-240V AC 50/60Hz, colour temperature 2700K ("warm white"), weight 125g, 108mm x 60mm, E27. I need to measure actual power consumption.
Update 2010/01/15: Swapped in the 7W/355lm "warm white" (2850K--3000K), CRI 70, 120° beam angle Aeon (Taiwan) ALTLED Aurora V3 M02GW007KC-90, -20°C--40°C ambient, 100V-240V AC, 50/60Hz GU10 spot/downlighter for my daughter's current bedside 3W 6000K LED, and it is as expected much brighter and warmer. It also looks a little more delicate (more fins at the front) and interestingly takes something like a second to switch on, and quite a few seconds to completely fade to off. (A quick test of the ES bulb in my desk reading lamp replacing a new 12W "softone" CFL seems satisfactory too, this evening.)
Update 2010/01/16: These new lights are going down well: we may well buy another couple of the EQ60s to replace failing or dead CFLs since we like the (warm) colour and haven't noticed any (eg RFI) problems... My power meter claims that the EQ60 draws 7.7W with a 0.45 power factor.
Update 2010/02/01: Waiting for 'production run' EQ60s warm and cool white for eval. Today bought 2W 'warm' Philips "AccentWhite" candle ES14 bulb for younger child's room as reading lamp for ~£9.