Viewing the internet, I stopped with this:

"Ampolleta de haluro metal dimeable" ("DIMMABLE MH bulb")

Can a MH bulb be dimmed? This is only mislead?

 

With electronic ballasts, yes, it is possible. The colour changes if you dim too much, though. They have circuitry to prevent the dimmer from working for the first 20 minutes after warmup to give the chance to get the lamp fully warmed up before dimming is possible.

Another setup is magnetic CWA ballasts. These have a capacitor in series with the lamp. By putting more than one capacitor in the circuit (I forget if they have to be in series or in parallel with each other), you can then wire up a system of switches where you take some out of the circuit or put them back in. It will give high-low settings only but it is still a rudimentary dimmer.

@sol this lamp is spetial for this porpuse? Or you can use any other MH lamp with the same power?

Another setup is magnetic CWA ballasts. These have a capacitor in series with the lamp. By putting more than one capacitor in the circuit (I forget if they have to be in series or in parallel with each other), you can then wire up a system of switches where you take some out of the circuit or put them back in. It will give high-low settings only but it is still a rudimentary dimmer.

I have a motor capacitive dimmer, and it connects in series with the motor; but i'll need a 65W MH lamp.

Electronic ballast can dim HID lamps, but this may lead with most lamps to color change (Aka greenish light in MH lamps or dim orange color on HPS lamps). Only special ceramic MH lamp with round arctube, can be dimmed with minor change or without change in color.

It is practically impossible to dim a high pressure lamp without consequences of a color change. The varying power levels will always cause varying arctube temperature, so varying fill pressures. Unless the lamp uses just a single dominant aactive material (like HPS or so; even there it has slight effect on the pressure broadening), each component will change its pressure in a different way, resulting in changing the component ratio in the arc atmosphere, so varying color.
But the point is, many applications are not sensitive to the color in the dimmed mode, as this is usually used just as means of energy saving during time when the top performance is not needed (merchandise illumination needs perfect color during shopping time, but provide just some security light at night,...)

Some makers did utilized the variable power to compensate for the lamp aging, either maintain the output (so the fresh lamps do not consume that much power, yet aged lamps are allowed to deliver the required light output - e.g. Venture used that) or maintain the exact color (stabilize the arctube temperature so the fill pressure, mainly used with white-SON, but as well with low power MHs - mainly those below 35W CMHs, car headlight during warmup use boosted power to compensate for the low efficacy of the not yet fully evaporated fill).
But these are in fact not really dimmable systems, just use the same HW functions to achieve something else.

Generally these functions come with electronic ballasts, because there it means no extra complexity to make the power variable, just the interface.