Why Would an LED "Bulb" Be Non-Dimmable?

[xrunner]

The pic of the package is attached. I don't have them on a dimmer, but I had been wondering why they would say it was non-dimmable? I know that LEDs can be PWMed and also be run at as low of a current as you want. So why do you think they say that on the package? What would happen if you tried it on a dimmer? 

[Arp]

Reckon if you run the leds directly from DC it will work with PWM but through the 220/110v AC/DC converter inside the lamp there are capacitors and stuff that prevents it

[c4757p]

Yep. It's not an LED, it's LEDs hooked up to a switch mode power supply/controller. That controller is going to try to give the brightness it's designed to give regardless of the dimmer TRIAC mucking about with its AC input, and will likely end up destroying itself in the process. Standard dimmers are only for resistive loads.

[mariush]

The electronics inside probably use something equivalent to Active PFC, boosting the input voltage to about 350v-400v, or it simply needs at least 90v or so to work right. Then a high frequency transformer is used to get whatever voltage is needed to drive those 9 leds, with a suitable controller to limit the current going through them.

Dimming is done by adjusting the ac voltage going to the lamp, so the lamp would have to work with wide range of voltages and also vary the current going through the leds to give the luminosity the person expects (led brightness doesn't always decrease linearly like a regular lamp's brightness decreases). 
It just adds a lot of complexity to the design.

[Rufus]

The pic of the package is attached. I don't have them on a dimmer, but I had been wondering why they would say it was non-dimmable? I know that LEDs can be PWMed and also be run at as low of a current as you want. So why do you think they say that on the package? What would happen if you tried it on a dimmer? 

Mains incandescent lamp dimmers apply a varying proportion of each half mains cycle to the lamp and rely on the thermal capacity of the filament to provide a constant light output.

Mains LED lamps try feed a constant current to the LEDs over the whole of the mains cycle and only need energy stored in a capacitor to cover the small gap around zero crossing.

Dimmable mains LED lamps need much more stored energy and circuitry to detect what proportion of the mains cycle they are being fed with to control the current through the LEDS.

If you run a non-dimmable lamp on a dimmer I imaging flicker will be very noticeable and effectively exposing them to turn on transients 100 or 120 times a second will damage them, possibly within minutes.

[muvideo]

Dimmable led drivers I've seen are high pf flyback,
the control IC usually can digest (or be adapted to
work with) "sliced" voltages.

Apart topology and driver, the other concern is
keeping the triac in conduction once fired, since
the holding current of the triac can be higher than
working current of the lamp, this results in triac
turning off too early and generates flicker and instability.
Another problem is damping the voltage spike
generated by the triac at turn-on, generated by
mains wiring inductance, this also can turn off the
triac soon after turn on.
A bleeder and damper can be simple capacitors and
resistors but dissipate some power, or be more
complex (and costly) designs that minimize impact
on efficiency.