Constant Current is the key, so 650 mA LED is not going to like 900 mA.
Getting LED lamps to work seems to be a problem, the LED can have thermal run away, so some thing is required to limit the current, be it inside the bulb or outside, but although the LED is DC the perceived brightness can be increased by pulsing the supply, so really looking at a RMS current valve not peak.
So three main methods of control are, the resistor, not good as resistor gets hot, but 3 LED's at approx 3 volt and a resistor at 3 volt on a 12 volt supply is common. Next is the capacitor, it has to be AC and at a set frequency, but it is the standard method with many 230 volt lights, and the last two names for basic same idea, switch mode power supply (SMPS), or pulse width modulated (PWM) power supply, so what it does in the main is turn the AC to DC, charge a capacitor, turn it back to AC at a high frequency so a very small transformer can be used, then back to DC, and either the current or voltage is monitored, and the info sent to the DC to AC converter, and it alters the on/off (mark/space) ratio to adjust the output.
In some cases the PWM is all built into one chip, so cheap they can be built into the bulb.
Also we have a problem because using a capacitor it can store the small amount of energy until voltage is high enough then discharge through the LED, so switched off with an electronic switch the LED flashes each time it builds up enough voltage, so a leak resistor is included to stop it. But the big problem is pulses DC unless smoothed causes the LED to flash although very fast, which can upset some photo sensitive people and machines (cameras).
This pulsing can also effect the next device, so a SMPS/PWM feeding a SMPS/PWM device can cause some very odd results. My electronic light switches (Energenie MiHome) needed a load capacitor across light bulbs to work. Even then it shimmered, so had to change bulb,
the large bulb has a smoothing capacitor in it and works OK, the small one also G9 has a shimmer. But there is nothing on the packaging to tell you why one works and other does not. In fact the large bulb should not be sold in UK as no lumen or watts marked on the bulb, but it works, and the small one that does comply does not.
The main problem is it is all trial and error, I have a draw full of new bulbs, that did not work, there is nothing to say which will and which will not work, so bedroom I NEED a remote control, so still use smart light switches, all other rooms removed, I still use plug in devices with table lamps, standard lamps and other mood lighting, but plug in, so can also unplug when it goes wrong.
Be it the AC, battery charger, outside light, display cabin lighting, kitchen floor lighting, or fan, I use plug in devices now, zigbee seems to date to work well, some times all built into the bulb, wife's bedroom two zigbee bulbs both work from same zigbee remote give mood lighting and lower light level to main lights. Two devices off same remote, however using phone one is colour changing can even have a blue light.
I was dead against using bulbs with built in zigbee control, I felt it was simply too expensive to replace if they failed, but compared with hassle of swapping light switches and sockets after they fail, it seems in hind sight better to use the bulbs, must admit with 8 bulbs in main chandelier, not so keen to use smart bulbs, but it is better than having to swap a smart light switch for a standard one when it fails. At moment I am using the old system, I tell the wife to switch on the lights, must get some return for money paid for marriage licence!
