ash, i think this lamp is using an 230v main led chip; so no driver needed. 

ash, i think this lamp is using an 230v main led chip; so no driver needed. 

LED chips alone could never be fed directly from the mains, they always require some ballasting.

There are chips marked as "120VAC", but that mean such chip is designed to operate from the 120V mains with simple series resistor as the minimum ballast of reasonable overall efficiency (~60..80%). These chips contain complete series chain string of about 30 antiparallel diode pairs integrated on the one, single die (and two such dies are then bonded in series for the "240V" device model of double the wattage).
With a bit more "advanced" ballasts the resistors are combined with a PTC (resistor split in half, one part bypassed by the small PTC - e.g. ACRiche from SSC these resistors are directly on the LED PCB module, so you then connect only the mains) in order to compensate out for mains voltage variation.

I have quite a few all work fine expect one failed right away but echanged it and all is good

(1) GE 7W spot. .3 diodes
(2) Philips 7W spots. .use 4 diodes
(1) utilitech 4W led globe dimmable but not in a dimmer. ..uses 1 dieode
(1) ecosmart 8.5W led dimmable. .has slight flickering problems when dimmed sometimes. .uses 2 diodes
(1) ecosmart 8.5 W spot led dimmable. ..uses 1 dieode
(1) 17W Philips ambient led dimmable
(2) GE .5W night light bulbs frosted

Longest led has been in use 3 years bout 3-5 hours daily sometimes dimmed down

I have  few of the CC crane plastic low power Led bulbs and they are crap! Lucky someone gave them to me
I will only buy metal heat sink leds that are high power not taking a risk with a failure prone plastic POS

@100Hz flicker:
I noticed, than the flicker visibility strongly depend on the duty cycle the light is ON versus OFF.
Light output of discharges with an inductive ballast follow more-less an absolute value of a sine wave, so most of the time in the half-wave they do emit light, so the flicker is not as visible.
On the other hand capacitive ballasts supply them with narrow pulses, so the lamps emit light only in one or two ms from the 10ms period. Although the frequency is the same 100Hz as before, the flicker become very visible, nearly even obtrusive.
I observed the same with discharges, as well as LED's. Even ~200Hz flicker of a LED flashlight on a low level setting (the output level is regulated by PWM, as it is the simplest method; for the lowest setting the duty become about 6%) become noticeable - I had to reprogram the controller to use 500Hz for the PWM, to supress that flicker.

@100Hz flicker:
I noticed, than the flicker visibility strongly depend on the duty cycle the light is ON versus OFF.
Light output of discharges with an inductive ballast follow more-less an absolute value of a sine wave, so most of the time in the half-wave they do emit light, so the flicker is not as visible.
On the other hand capacitive ballasts supply them with narrow pulses, so the lamps emit light only in one or two ms from the 10ms period. Although the frequency is the same 100Hz as before, the flicker become very visible, nearly even obtrusive.

I seen the same 100Hz flicker with ordinary F36T8 on Switch Start inductive (2 lamp fixtures, 2 inductive ballasts, 1 8uF PFC parallel to the AC input), and i am not sure what exactly causes this - as it sometimes does happen or not happen with the same lamps

@Ash: The flicker of discharges may be of many kinds, as the discharges tend to be generally very temperamental:
Normally on the inductive ballast, the flicker is mostly unnoticeable, as the lamp glow pretty uniformly over more than 1/2 of the half wave.
But:
- For your view angle, one side could contribute way more to your perception than the other end of the tube, so the presence of the cathode dark band when the closer end is negative cause the perceived 50Hz flicker
- The tube could rectify, causing 50Hz flicker component
- The arc in the tube could create bright "filaments" move them around the tube, what yield a flicker in the frequency range of few Hz to few 10's of Hz. This could be the case even for HF ballasts and even for those operated from batteries.
- The ballast choke could slightly saturate, so create current spikes around the top of the current waveform, effectively causing low duty 100Hz flicker, what become visible
- The lamp is very bright and in your peripheral vision, where the eye is most sensitive for any movement, so even the normally unnoticeable flicker become disturbing. In that case would be good to rearrange the lights or your working position (move the desk,...)

today i opened an mr16 led lamp made by lexmann.
it use luxeon rebel leds!
also, driver is quite well made: except of base connection (it is solderless), it is well soldered; it have 105°C 25V electrolitic capacitors (but unknown brand), a bit of thermal grease, hard plastic protection with a very strange opening protection (you have to remove lens, led module and finally you can remove ballast removal protection, so you can twist ballast and take it out).
i paid 9.90€ for this last year and i reassembled it to future use.
this lamp is not dimmable, but i managed to dim it for nativity scene of this year.

Electrolitic capacitor can be a source of trouble. Not all of them are the same and not all the data written on them (other than go look in the datasheet)

They can have different ESR. High ESR = high heat in the capacitor

They can be different dimensions. When 2 capcitors have the same ratings (including ESR) but one is 2x bigger, guess which one will last longer ? (This have basically to do with ESR and surface area of the conductors and the case to dissipate the heat)

They can use different quality electrolyte

What brand they were ?

i didn't write it down (now i reassembled light), but seems unknown brand (no rubycon, panasonic end reputable brands); i'm planning to replace them with rubycon.

You have to be very careful in the exact type: Even when you use the reputable brand, if it would not be the power rated type, it would fail pretty soon...

You have to be very careful in the exact type: Even when you use the reputable brand, if it would not be the power rated type, it would fail pretty soon...

i think something with 2A on ripple current would be fine on 250mA load 

2A rated capacitor won't fit into such small MR16 enclosure, you would be happy to find some 200..300mA one...

update: i bought other lamps, including some ikea ledare.
all lamps works fine, i also made an light with an 12v 10w led spot (when it overheat, it flashes because thermal protection).

...it flashes because thermal protection).

That mean it's thermal design is inapropriate and it uses a driver chip not suitable for LED's:
Generic SMPS have to either deliver the rated power, or completely shut down, preferably with some prewarning, in order to avoid erratic behaviour of the supplied equipment.

Specialized LED supplies are on purpose designed to gradually reduce the power when they heat above certain limit, so the thing find it's thermal equilibrium point without visible effects like flashing or so and yet prevent the system from overheating. The reduced brightness is then usually not noticeable...


Well, personally I'm not as much sure, which approach is better. The first one clearly show, there is something bad with the light (it overheats...), what should be addressed.
On the other hand, the second allow to operate the system with tighter thermal budget without artifacts. If designed reasonably (the regulated temperature isn't too high), it may really allow to utilize maximum possible output the circumstances (ambient temperature, air movement,...) allow, without excessive degradation.

That mean it's thermal design is inapropriate and it uses a driver chip not suitable for LED's:

no, it's just my thermal design in torch: because i didn't designed it for long operation in hot climate, i use some pipe (pipe torch  )