Question: We have four LED spot lights or down lights maybe, at 12V (AC/DC), 10W. (We don't have any more information unfortunately) We have them connected in parallel with a driver that outputs 15-34V at 1500mA. This driver also buzzes slightly in this setup, but we're not sure if that's a separate problem.

When we turn this on, the LEDs give a constant light, but at a very low luminosity. With only three LEDs in parallel on this circuit, the LEDs do a slow flicker (a couple of times a second perhaps).

We've tried with a different driver (22-38V, max 50V, 1050mA) and the 4 LED setup flickered slowly again.

Does anyone know what is going on and what sort of driver is necessary? We're banging our heads against the wall here

Thanks!

Answer: 
This is your problem:

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We have them connected in parallel with a driver that outputs 15-34V at 1500mA. 

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That is a constant current driver that operates between 15 and 34Volts. Your lamps operate at around 12V. The current regulator can't operate that far down, and so isn't doing its job properly.

For this to work right, you would need to put the lamps in series. That won't work for all four, though, as neither of your regulators can go up to the 48Volts that the four lamps in series need.

Since you have two power supplies at hand, try this:
Wire two lamps in series to each driver. That gets the required drive voltage into the middle of the range for both power supplies, so the regulators should work properly.

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It is in general a bad idea to put LEDs in parallel because the voltage at which they turn on can vary a little bit. The LED that turns on at the lowest voltage gets all the current, which could cause the LED to burn out.
The LED's rating (12V, 10 W AC/DC) suggests that it has an built-in *current source* (i.e. a current limiting resistor or a more sophisticated circuit). In this case, you need to apply a voltage source rather than a current source. As your LED driver outputs a constant current, adjusting its voltage accordingly, the LED's internal driver does not work as intended, as it requires a 12V voltage supply. 

Using a >=60W 12V DC power supply, you can connect all LED spots in parallel and you will be fine.

**However:** You should double check to verify that the LED spots do have an internal current limiting circuit. If this is not the case, using a constant voltage supply **will cause permanent damage to your LED spots due to over-current**. Perhaps there's a product code or other device specific information on the LED spots that may help you to identify the product and gather further application information. 

Additional note:

If the spots can be used as a replacement for conventional halogen spots, then they *most probably* contain some sort of current limiting circuit, as halogen power supplies are voltage based.