LED lights

[gvasale]

What is it with many if not all LEDs that makes them painful to look at? Any type of filter that may help improve the quality of light?

[Evan]

The eye judges brightness based on the amount of light focused on the retina per unit area in the fovea. The fovea is the small spot in the central portion of the eye which has a very high concentration of colour receptors and is the only part of the eye with high resolution. Because the actual emitting area of an LED is very small it is correspondingly brighter per unit area and so is the flux of the focused image on the retina.

That focused image can be brighter than the focused image of the sun. While it doesn't contain the UV or IR that causes damage it still activates the "it's too bright to look at" protective response in the brain.

As for a filter, any sort of diffuser will do quite well. For example, my main ceiling light contains 4 emitters that are very painful to look at so they are behind a diffuser.

I also use shielding fixtures to ensure you don't see the high power emitters directly.

[MotorradMike]

I think part of the problem is the spectrum emitted by "White" LEDs. There are generally 3 peaks with wavelength gaps. I'm guessing "Natural" light on a cloudy day is about the same energy per wavelength. The LEDs look white but they are fooling your eyes.

Evan tried to explain this to me once but I still don't get it. I know the spectrum can be adjusted to give warmer or cooler light but all the spectra I've looked at still have those 3 peaks.

If you shine a LED flashlight on a photograph it doesn't look the same as if you use natural light.

[Evan]

You may not be interpreting the wavelength chart correctly. Below is the official data sheet information for the latest Cree XRE-7 emitters. The red, green and blue lines do not represent the mix of colours in the emitter. They are simply colour codes for the three different types of white emitters listed on the right. The red line is for the warm white emitters with a colour temp of between 2600K and 3700K. As you can see that line includes a full spectrum of light including the very near blue/UV found in daylight. It is shifted toward the red the same as an incandecent lamp. The other lines also cover the entire spectrum with corresponding shifts toward the blue. 6500K is the same as sunlight. Anything higher will be more blue and anything lower is a warmer spectrum.



The 6500K emitters have excellent colour rendition, far better than either incandescent or fluorescent lighting. My wife makes art cards and uses special colouring pens that come in 250 different shades. She loves the white LEDs I installed for her in her workshop since they give by far the best colour definition.

[Ian B]

I'd guess it's because the light comes from a pinpoint, of a much smaller surface area than an equivalent wattage incandescent or fluorescent. Try staring at a halogen head-on, same effect.

On the subject of colour; the general opinion is that LED's give a 'cold' light - maybe too much blue for our liking, or when compared with incandescents. Maybe it's possible to mix a few reds or yellows in with the whites - relatively easy when you see the bulbs coming out that contain arrays of up to 48 LED's in a tight cluster. Might make the light a bit warmer.

Ian

[Ian B]

Evan beat me to it.

Evan, the LED's you mention taht put out a colour temperature of 6500k may be excellent for photography, but I wouldn't want to light my living room with them. A warmer light is more pleasant.

Ian

[Evan]

I dislike warm white light, especially in winter. 6500K light is much more effective in fighting winter depression caused by darkness.

[vpt]

I agree and not sure if it is the same thing you guys are talking about but I dislike the "pulse" you get from LED's. Looking at LED's the pulse of the light almost give me a seizure.

[Evan]

Some chaep LED lights don't have switch mode power supplies. Instead they are operated using a capacitive reactance current limiter. These flicker badly and are definitely not worth buying. Properly made LED lights use filtered switch mode power supplies and do not flicker.

[2ManyHobbies]

I dislike the blinking cheap taillights in expensive cars. One glance down at the instruments then back up at night and you are surrounded by angry red spots.

It sure makes me appreciate the quality of the better devices out there.

[MotorradMike]

I'm still confused about the emitted spectrum.

Looking only at the blue plot in post #4.
The chart shows a huge peak at 460nM and a lesser peak at 560nM.
Are you saying that flat natural light through cloud would have a similar distribution?

I would have expected a far flatter curve similar to one for white noise.
Roughly equal power per wavelength.

[Evan]

The proper way to interpret that sort of chart is to calculate the area under the curve. Looking only at the peaks doesn't tell the story.

The area under the curve for that plot is 310 (dimensionless number) for green to deep red. Between green to violet it is 83 and for long UV it is 69. The bulk of the power is in the red to green range and the total power in the visible spectrum is 85% of the output.

I calculated the areas under the curve with SketchUp by tracing over the image and then selecting each section. Sketch automatically calculates the area.



The solar spectrum exhibits an exponential power spectrum with frequency up to near ultraviolet so it is far from flat.



Based on this comparison the 6500k LED is still warmer than sunlight, especially sunlight filtered through clouds which may have a colour temperature as high as 10,000K.

[macona]

I dislike warm white light, especially in winter. 6500K light is much more effective in fighting winter depression caused by darkness.

I agree. I use 6500k CFLs and a 6500k 70w metal halide in my front room. Good for my birds too.

[Rich Carlstedt]

Evan
The strip lights I put under our kitchen cabinets ( Hera LinkstripLED/WW ) says this:
"Caution:
Customer also acknowledges that light from LED's is bright and may be intense enough to injure human eyes. Individuals should wear proper protective eye equipment at all times and not look directly into LED light. Further, individuals should not look at reflected light originating from the LEDs for more than 60 seconds "
They are one watt per LED (3000K ) ?
and the strip is 5 feet long with 15 LED's

Is this reasonable?
Should I be concerned, or is this just lawyer lingo like the warnings on a Mc Donalds Coffee cup ?
What kind of eye protection would be needed ? The bare light is very disconforting,so we stay away from that, but reflected light ?
There is a difusser cover strip on them. They work so well, I was thinking of making a ring light for the mill, but have this concern, as that would be exposure far more than counter top work.
Thanks
Rich

[Evan]

Further, individuals should not look at reflected light originating from the LEDs for more than 60 seconds "

That must be from the same people that put "Do not eat" on dessicant packages found in shoes. I generally don't eat anything that I find in a shoe.

There is no danger whatever.