Everyone else is right, but to answer the question directly:
The force on the light due to drag is:
D = q * S * Cd
Where q is the dynamic pressure, calculated by q = 1/2 * rho * V^2, rho being the density of air and V being the airspeed.
S (or A) is the frontal area, which you said was 6 in^2
Cd is the drag coefficient, which varies depending on shape.
A cube has a Cd of 1.05 (no relation to Cubes who has a very low drag coefficient). A flat plate is about 1.3, per
https://www.grc.nasa.gov/www/k-12/airplane/shaped.htmlUsing metric units (sorry):
V = 82 m/s (160kts)
Rho = 1.225 kg /m^3
S = 0.004 m^2 (6 in^2)
Cd = 1.3
Calculating...
D = 21 Newtons or 4.8 pounds.
4.8 pounds is not a lot of force, so depending on the actuator and linkage geometry, it should be quite reasonable. If the light is mounted fixed, this is roughly the force that it will impart on the surrounding structure. Note that the Cd estimate is for a free flying flat plate. Mounting the light against a wall may decrease the drag coefficient.
As a side curiosity...
Power is drag force times speed, or P = D * V
4.8 pounds of drag at 160 kts requires 2.4 HP to push. That's more than 10% of my engine, so even though it's not a lot of force on the structure, it could impact your top speed if done improperly.
There's another thread about maximizing speed and another about action camera mounting externally. Appendages aren't a big deal structurally, but a clean airplane goes fast.