I love the LED projects, and the format of the show now

[G+_Walter Riggs]

I love the LED projects, and the format of the show now. I was on track to start replacing all of my home bulbs with LED from Cree until I saw a high speed movie taken of one, and it was flickering like crazy. Is this due to AC electricity going to the bulbs (or the LEDs in them)? Is it just a thing that all LEDs do? What are the eye strain concerns with a room light with these bulbs? I'd love to see some show address these issues and this seems like exactly the place.

[G+_Eddie Foy]

A high speed cam?  Stop.  Your eye can't see beyond x cycles a second (forgot the Hz)

 

Its flickering because an LED the D being diode, is rectifying the AC.  It is only using 1/2 the AC cycle. AKA: its only on 1/2 the amount of time.  Caps and filtering  of even semi-quality bulbs should smooth it all out for eyestrain.

 

As a HAM radio operator, I can testify that LED bulbs are WAY 'quieter' then CFLs.  (we tend to avoid at all costs EMI/RFI)

[G+_Jason Marsh]

It's an artifact of the 60Hz power supplying them. I wouldn't worry about it because it's imperceptible to most people. Fluorescent lamps have been known for this forever, and that didn't stop them from taking their throne as king of retail space lighting. As Eddie Foy mentioned, you won't be able to see it. If you are lighting a studio, though, you probably won't want them unless your video gear can sync with or counteract the flicker.

[G+_Daniel Armstrong]

There are 2 types of LED bulbs sold, 1. those with a capacitive dropper, IE using the reactive impedance of a capacitor to limit the current, and 2. those with a constant current power supply/driver. The capacitor based ones are sold as non-dimmable and the driver ones may or may not be dimmable.

 

The light ripple of capacitive dropper ones depends on how big of a smoothing capacitor they used. It is a tradeoff, too big and even with a discharge resistor across the LEDs you will have afterglow, IE when shut off the light will fade out. These also can't be used on a dimmer since dimmers create high frequency harmonics and since the impedance of a capacitor goes down as the frequency goes up when you try to dim them the current can actually go up and damage them.

 

Driver based dimmable ones are intentionally off during the AC sine zero crossing, as that is how they dim. AC light dimmers chop off part of each alternation to extend the zero crossing duration. Leading edge dimmers crop the beginning of each alternation and trailing edge dimmers crop the end of each. What you end up with is 100 or 120Hz PWM depending on your line/mains frequency.?

[G+_Robert Hafer]

I have several Cree bulbs (all dim-able) and can't detect any flicker with my mark one eyeball

[G+_Walter Riggs]

Yeah of course, the brain's not going to see any flicker, but I recall reading that the iris of the eye still reacts to office fluorescent lighting (can't find that old article at the moment). I started wondering about this last winter when I put xmas lights up around the house that were LED. When looking at them against the house/bunches at night they looked different from the old filament lights that we replaced. We couldn't really focus on individual bulbs. So I started googling around and found this flicker effect. I was wondering if this was a result of plugging them into AC power. What if I made a string powered by a DC wall wart? Would they flicker then? My LED backlit TV and monitors don't flicker when I take a slow motion video of their screens. More experiments are required I guess.

[G+_Daniel Armstrong]

LED Christmas/faerie lights are usually only half wave rectified, hence they flicker at 60Hz instead of 120, and to add insult to injury the forward voltage of the string is high enough that they are only lit for about half of the alternation, so a quarter of the time total. I see the flicker and it gives me a headache.

 

I couldn't use a CRT computer monitor at 60Hz for the same reason. 75Hz was bearable and 85Hz was smooth for me.