Today there is a growing trend for active cooling of high power, high output LED products.  Active cooling (rather than passive) means that it uses energy, usually in the form of electrical power.  There are several techniques; there are Peltier Cells, there's one with a diaphragm to pulse air across a finned surface, and one popular and effective method utilizes a fan.  Initial response from most LED advocates:  It's a crazy idea.    

          "Why add moving parts to a solid state device?"

Fans work well, but ironically, their most prevalent failure mode is not what you might expect.  Some of the fan sales efforts may claim life double the hours of anything practical in outdoor environments. 
Read on to see why the fan and LEDs cannot do this.

Here I will comment on some of the pros and cons with a fan concept.

Pros
1st - there are fans than can provide 100,000 hours of operation, and that are reasonably quiet.   28dB(A) at 1 meter
2nd - when in operation, this fan levitates the rotor off the bearing for non-metalic contact.  This is key to its longevity.
3rd - the fan can be likened to a 'fin area multiplier' allowing the otherwise passive surface area to be reduced by a couple orders of magnitude.
4th - actively cooled LED assemblies can be smaller (if fan is smaller than the passive fin area it replaced) and IF the moving air can itself be cooled.

Important to note that a fan inside an enclosure is only moving heat away from the LED module as hot air, and that heat must be dissipated to the enclosure interior surface.  The outside dimension of the enclosure must still have adequate surface area to convection cool the assembly based on the wattage dissipated by the LED system.  In essence, the fan is replacing the thermal connection between LED module and the enclosure surface with a moving stream of hot air.  It requires a good thermal connection between that hot air and the interior surface.


The Downside
Almost all reviews, comments and sales pitches for the fan are based on it running, INDOORS with controlled environment.  Remember, its life must exceed LED life.
    But what about when the fan is NOT running, especially if used outdoors?

A review of the specifications of the MagLev fan disclose some sensitive issues, some of which they strictly forbid.
1 - operating and storage upper temperature limit is 70°C
2 - operating and storage maximum relative humidity 65% non-condensing
3 - no water droplets, no condensation, no dew, no salt, no bugs
4 - if the MagLev  fan is stored more than 6 months, they advise it should be tested before installation
5 - all factory testing shown in data sheet is at 25°C and 65% RH
6 - there must be circuitry to detect if the fan fails (i.e. excessive temperature), and shut down the device

It is a fact that an outdoor enclosure exposed perpendicular to the Sun's rays can reach 85°C internal temperature. Ref: Prior to finalizing the LED Traffic Signal Specification in 1996, the ITE did a national study in virtually every major city to establish maximum operating temperature requirements for LEDs in traffic signal housings.  These measurements were for non-powered traffic signal heads.

Following the rules for humidity and condensation, if used in an outdoor application, the fan must be in a sealed enclosure.  A simple rain shield or cover that allows humidity to reach the fan is unacceptable.  The outdoor environment will almost always have condensing humidity numerous times during the year; some geographic locations far worse than others.  This is also known as the dew point. 

Electronic control with special thermal design features can manage these conditions, e.g. turn the fan on to cool itself or dry up condensation if the device always has power applied.

In an enclosure, all the laws of square inches per Watt at the outside interface still apply.  In fact, they are more critical with fan cooling (rather than direct contact) inside an enclosure because few designers add fin area to the inside surface of that enclosure, making that air interface to enclosure a much higher thermal resistance (°C/W) than that between the LEDs and its fins.  The active cooling design will almost always have higher thermal resistance between the hot air and outside convective surface due to inadequate surface area inside the enclosure.

Some products that have fans in their designs may have claims they will produce light even if the fan fails.  Clearly, a fan type design has far less fin surface area on the LEDs, so if there is no fan action, there will be little or no cooling and any light produced will be insignificant.  A fan failure must be repaired.

Interim Conclusion
Active cooling may be controversial.  The comments on efficiency regard cooling only, but might reduce the size by reducing fins. 
When used in outdoor lighting, some automatic (photocell or time clock) applications may have the lights and fan ON when the dew point is reached, and possibly avoid exposure to that condition outside the specification.  However, outdoor lighting not in an enclosure, that is used only for periodic (not daily) illumination, will most assuredly be exposed to inclimate conditions forbidden by the fan specification.  Any outdoor application in an enclosure can expose the entire assembly to extremely high Solar temperatures unless the design offers protection, such as running the fan, or providing a Sun shade.  Even with the fan running, some outer surface of the enclosure must be cool enough to lower the interior temperature to 70°C to comply with fan specifications, and that cooler surface must convect more internal air than the solar heated surface.  If in LinkedIn, click LinkedIn Comments on Fan Cooling to see world wide opinions.