> > I paint my hives dark to get more heat... If you look at the
> > hive from a heating/cooling point of view, you have two
> > competing dynamics
>
> I am wondering what effect "blackbody radiation" theory would
> have on this technique ...although a dark hive will absorb more
> solar radiation than a light hive when the sun is shining on
> it, it will also re-radiate to the atmosphere MORE HEAT when
> the sun is not shining on it. Thus cooling the dark hive more
> than a light hive.

This is something that I have often thought about.  I guess that the
long and the short of the matter is that a beehive is not a simple or
inert heat system.  Complex and variable factors are involved.  Internal
convection and heat conduction come into play along with other
non-linear factors like the metabolism of honeybees and their response
to stimulae such as heat inputs and external temperature changes.  The
bee responses may vary with season and faecal or disease pressures as
well as recent hive history.

I don't frankly understand the system (hive plus bees) well enough to
analyse it properly, although others with engineering training have made
some interesting attempts.  One such analogy is the 'chicken in a box'.
I'll merely try to outline the factors as best I can here and hope that
others will contribute.

First bees are not inert matter, such as we generally use in undergrad
lab experiments at university when studying heat transfer.  They are
living organisms and the colony is considered by many to be a
superorganism.  As such, the bees respond to heat input with heat
effects of their own, such as raised or lowered metabolism and fanning
or moving to contact hive surfaces.

I think it is safe to say that it is generally believed that it is good
for the bees to be able to expand their cluster and become active during
the active season.  Of course there may be exceptions to this in
wintering conditions, but generally, warmer is better -- until we reach
temperatures that start to cause discomfort or an excessive work load in
dumping heat.  This can occur when the temperatures get into the high
thirties and forties Celcius; bees may cease all other activities and
find it necessary to devote all their resources to maintaining an
non-lethal hive temperature.  Their cooling efforts use energy and when
they reach some level of heat input, these very cooling activities can
culminate in a heat 'avalanche' if they have restricted air passages or
lack of water.

Anyhow, the theory is that the initial application of heat from the sun
warms the hive and dormant bees and they then start up their dynamic and
complex heat management systems which function until cold and darkness
cause the bees to again return to semi-dormancy and the hive again
becomes a somewhat inert heat system.  The initial absorption of heat
from the sun by darker boxes causes an earlier triggering of this
activity than is the case with light colored or shaded boxes.

There is some controversy as to what is ideal, and understandably, the
opinions vary geographically, with the strain of bees used, the
beekeeping techniques employed, and the ultimate goals of the beekeeper.
Suffice it to say that heat stimulation, like any stimulation can be a
good thing.  Using dark boxes or wraps can increase this effect.

When the sun goes away, there may be an initial more rapid cooling of
the outer surfaces of the box, and conduction and radiation of the inner
heat that is greater than would be the case with white boxes, however at
this point, the bees are active and heat loss is not a problem, since
they can make it up if they so wish.  If the day is ending and light
stimulus is removed, the more rapid loss of heat may trigger a shutting
down of activity sooner than with white boxes, but once the bees return
to quiescence, they are clustered and mostly unaffected by ambient
temperature.

In northern areas, most beekeepers believe that a bit of warming helps
the bees break winter dormancy to deal with some important issues like
moving to new stores and allowing old bees to leave the hive.  If not
carried to the extreme where feed consumption becomes excessive, this
results in healthier hives.

having said all that, I must admit that my hives are white for the most
part.  My winter wraps, however are black.

FWIW

allen