LED lighting

Advert

New Replies

Report Bug

Help/FAQs

LED lighting

This topic has 38 replies, 16 voices, and was last updated 2 September 2018 at 12:47 by Muzzer.

Viewing 25 posts - 1 through 25 (of 39 total)

1 2 →

Author

Posts
26 August 2016 at 17:23 #252385
Geoff Theasby
Participant
@geofftheasby
Can't find the recent discussion on this topic, but spurred on by it, I bought a reel of LEDs with adhesive backing, running off 12 volts and trimmable to length. This was because one of my basement fluorescents packed up, with a faulty fitting. A new one is £18 and tubes about £5. These LEDs cost £7 for 5 metres (600 in quantity, or about 1p each) I cut off 600mm to go under the shelf over my computer, fed it with 12 volts from a redundant 'wall wart', and Shazam! Let there be light, and there was light, and Lucifer was consigned to the outer darkness. Now, simple unrectified/unregulated power supplies may cause the LEDs to flicker when looking directly at them, but the reflected light appears steady. As LEDs are diodes, they only conduct every half-cycle of the mains, so appear to flicker at 25 Hz. Rectified power supplies, which provide DC, should not have this problem.

Geoff
Advert

26 August 2016 at 17:23 #31851
Geoff Theasby
Participant
@geofftheasby
26 August 2016 at 19:03 #252396
duncan webster 1
Participant
@duncanwebster1
I must be doinfg something wrong, so some clever bloke tell me what it is.

LED strip light on e-bay quotes 14.4 watt/metre consumption and 420 lumen/metre output. That is 29 lumens/watt. The wall wart will not be 100% efficient either, some are dreadful.

GE fluorescent tubes quote 2850 lumens for a 36watt tube. That is 79 lumens/watt. seems to me I'm better off sticking to tubes, but others rave about LED so where am I going wrong?
26 August 2016 at 19:20 #252403
Neil Wyatt
Moderator
@neilwyatt
Various reasons, some are:

The difference of about one stop is not huge (2:1 ratio) and the eye will probably adapt to the difference

LED 'white' light is very blue and all in the visible while some fluorescent light is in less efficiently detected parts of the spectrum.which can create the impression of greater visual brightness.

LEDs throw all their light down and out, while the tube sends half of it up to bounce off the luminaire or ceiling, losing a fair percentage in the process unless you have an expensive mirrored luminaire

Neil
26 August 2016 at 19:51 #252416
Geoff Theasby
Participant
@geofftheasby
What Neil said. It's like the difference between a plain bulb and a spotlight. Checking with my photographic lightmeter reveals an illumination difference of 4 x between the 4 foot fluorescent tube and the LED strip, with the tube light being brighter. However, the eye perceives little difference (on a logarithmic scale) the LEDs are mechanically robust, and consume far less energy, besides costing less in capital outlay. If you need more light, a second or third etc., parallel strip may be fitted for a few more pennies.

Geoff
26 August 2016 at 19:54 #252417
Geoff Theasby
Participant
@geofftheasby
Neil, do you mean these?

Geoff
26 August 2016 at 20:08 #252425
Michael Horner
Participant
@michaelhorner54327
Hi Geoff

Have you mounted your LEDs to a heat sink? I made some under cupboard lights out of LED strips and they deteriorated overtime which I put down to heat, The ones for my workshop I mounted on an aluminium stip and they seem to have lasted better.

Cheers Michael
26 August 2016 at 20:27 #252431
Muzzer
Participant
@muzzer
Indeed, heat (temperature) is the enemy of the LED, so most high power LEDs are mounted on IMS. And the general rule for electronic components is that every 10C rise halves the life and doubles the failure rate.
26 August 2016 at 20:34 #252432
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by Geoff Theasby on 26/08/2016 17:23:56:

As LEDs are diodes, they only conduct every half-cycle of the mains, so appear to flicker at 25 Hz. Rectified power supplies, which provide DC, should not have this problem.

The flicker will be at 50 Hz with half wave rectification. With full wave it will be 100 Hz but at a much lower level.

Russell.
26 August 2016 at 23:06 #252449
Geoff Theasby
Participant
@geofftheasby
Michael, no.

After being ON all day, they are still cool to touch (Stuck below a wooden shelf) whilst the supply is only warm. If it proves to be a problem, replacements are quick and cheap, or aluminium strip can easily be inserted.

Geoff
27 August 2016 at 00:07 #252452
Ajohnw
Participant
@ajohnw51620
I'm thinking of trying these for a machine light – on a mill. I'm happy with the one I've mentioned before on the lathe.

RwAAOSwe7BW0Blx”>http://www.ebay.co.uk/itm/Black-30W-1200LM-U2-Motorcycle-Car-Bike-Motorbike-LED-Laser-Fog-Spot-Headlight-/262308258436?hash=item3d12ca6284:gRwAAOSwe7BW0Blx

These because I know from others that the "glass" needs to be shaped in that sort of fashion to get an even pool of light and with luck they may have done it properly.

The box they come in states 12-60v AC or DC. Actual consumption 6 to 9w. Construction is interesting. The back screws off and it looks like the led is positioned somehow and the potted in clear epoxy also forming the lens. Then some black epoxy on top of that.

People often talk about lumens but there is a need to get one's head around these 2

**LINK**

**LINK**

and what we are really interested in is the illumination levels at the "surface" we want to light = lux. Frankly I don't think that a lot of Chinese led strips or leds are rated correctly. They put out a lot of blue and the eye sensitivity factor isn't accounted for which makes them sound brighter. The 3 colour output can make measurements difficult as well. A meter might record the blue completely where as out eyes are not very sensitive to it.

John

–
27 August 2016 at 07:26 #252460
Geoff Theasby
Participant
@geofftheasby
Sorry, Russell, yes.

John, white LEDs are actually three differently coloured devices in one package, possibly with two blues, since they need to seem brighter, as stated, making four. Then a phosphor is applied overall, which glows white. I will have a look at them using my photographic filters, to see if anything is revealed. NB, this is off the cuff, I haven't checked it for accuracy.

Geoff
27 August 2016 at 08:30 #252465
Les Jones 1
Participant
@lesjones1
Hi Geoff,
Are you sure that ALL white LEDs are made from three coloured LEDs ? I was under the impression thet white LEDs were actualy UV LEDs with a coating of phosphor to convert the UV to white light.

Les.
27 August 2016 at 09:26 #252474
Geoff Theasby
Participant
@geofftheasby
Les, I found this just now.

https://en.wikipedia.org/wiki/Light-emitting_diode

Geoff
27 August 2016 at 09:35 #252476
Michael Gilligan
Participant
@michaelgilligan61133
Geoff,

Count the connections to the LED … If you only have +ve and -ve, then it's almost certainly as Les says.

A short wavelength Blue emitter, which activates a yellow fluorescence in the phosphor. … The combined light is approximately white.

RGB packages have more connections.

MichaelG.
27 August 2016 at 09:44 #252478
Ajohnw
Participant
@ajohnw51620
They aren't exactly UV led's and a phosphor as I understand it. The blue is sometimes called dental blue which is getting towards UV.

This is what tends to come out of a typical higher than usual power led – it's on the wiki page linked to

The blue is what excites the phosphors for the other colours. I've not seen any with a blue phosphor but have seen then with an extra green and an orange. The blue is often rather high in order to obtain a higher colour temperature and has to be because our eyes are not very sensitive to it. It's a lot lower once the colour temperature is down to around 5000k. It's still a spike even then but usually around the level of main colour hump or lower.

Just add that sometimes LED's and lights are available in more than one colour temperature and the lower colour temperature always outputs less lumens but is also often more efficient. All down to our eyes inefficiency at the wavelength of the blue used. As the excess blue ones had a short term effect on my eyes I wont go near them any more and even sometimes wonder about PC screens but suspect they use a different blue.

John

–

Edited By Ajohnw on 27/08/2016 09:51:26

Edited By Ajohnw on 27/08/2016 09:52:06
27 August 2016 at 09:52 #252481
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Ajohnw on 27/08/2016 09:44:46:

They aren't exactly UV … The blue is sometimes called dental blue which is getting towards UV.

.

Nice exposition of what I said, John
27 August 2016 at 10:12 #252485
Ajohnw
Participant
@ajohnw51620
Posted at the same time Michael.

If anyone is curious about led's this site has good data sheets – makes very good led's too.

**LINK**

They even make one now since last time I had an interest that is said to dim following black body radiation patterns, sic. Interesting to see what the blue does to achieve that and no way is it the same as black body radiation really.

John

–
27 August 2016 at 10:30 #252493
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Ajohnw on 27/08/2016 10:12:34:

Posted at the same time Michael

.

"Great minds …"

MichaelG.
27 August 2016 at 19:57 #252606
Geoff Theasby
Participant
@geofftheasby
Well now, Michael, the LED packages are two-terminal. The photographic filters reveal one main light spot in the centre of each package using any colour. The LEDS are on a reel, probably soldered & mounted automatically. Obviously, the diodes must be the same way round, ie anodes together, cathodes together. So, they are probably as Les said. Thank you, Les.

Geoff
27 August 2016 at 20:48 #252624
Ajohnw
Participant
@ajohnw51620
Possibly unlikely in this case Geoff but other things in the led package may make it happy with ac or dc either way round. it doesn't take much in them to do that. They are very likely to have something in them to limit the current each one takes.

John

–

Edited By Ajohnw on 27/08/2016 20:48:38
27 August 2016 at 20:55 #252625
Neil Wyatt
Moderator
@neilwyatt
Totally random, but this closeup of a phone display may be of interest, I can't remember if it was LCD, LED or OLED. Although he filename claims it was LCD I would expect larger square pixels with LCD so I guess OLED. Interesting how little of the area actually lights up.

Not bad for 200x with a £30 microscope.

Neil
27 August 2016 at 22:39 #252636
Michael Gilligan
Participant
@michaelgilligan61133
Here is the 'retina' display on my iPod Touch, for comparison:

Interesting structural differences.

MichaelG.
28 August 2016 at 08:48 #252659
Neil Wyatt
Moderator
@neilwyatt
Posted by Michael Gilligan on 27/08/2016 22:39:28:

Here is the 'retina' display on my iPod Touch, for comparison:

'Retina display' is cunning marketing. Even an old 625 line TV is 'retinal' at the correct distance!

Neil
28 August 2016 at 09:27 #252668
Michael Gilligan
Participant
@michaelgilligan61133
Predictable response, Neil

You are of course correct in that statement, but that's not really relevant to the point I was making.

The real origins of the 'Retina' name were explained in the early days, but I'm blowed if I can find any reference now … Because Apple adopted the 'retinal resolution' aspect as the marketing message. **LINK**

The origin of the name was to do with the innovative construction, which allowed the sub-pixels to be more closely packed … This involves putting some of the wiring in front of the light emitters, and is therefore reminiscent of the way that our own retina is built [with the nerve layer in front of the receptors].

I didn't post the photo for any sort of 'competition' … Just to show a different bit of engineering

[quote] Interesting structural differences. [/quote]

MichaelG.
Author

Posts