The plans from Wildstone Estates Limited for the site in Shirley Road were also deemed to harm visual amenity.
The proposal for the LED advertising display was previously turned down by Southampton City Council planning officers who believed it would impact on the character of the area and public safety.
Wildstone Estates launched an appeal to the Planning Inspectorate challenging the decision of the local authority.
A statement prepared on the appellant’s behalf by Stantec UK Limited said the reasons for refusal given by the council were unjustified.
The scheme, which was planned for the IMO Car Wash site, would show multiple static advertisements on rotation, with a “high level of control” over the brightness.
The appeal was considered by government-appointed planning inspector R Cahalane.
A report by the inspector said the blank side, which would be “clearly visible” from Shirley Road and Malmesbury Road, would harm amenity in visual terms.
“This would result in a prominent and alien addition to the streetscape, accentuated by its location and freestanding form that would disrupt views of buildings beyond,” the report said.
In relation to the display screen, the inspector said its slight elevation, changing content and position in relation to a nearby zebra crossing could divert a driver’s gaze away from the road ahead.
They added: “This would likely cause drivers to be distracted from dynamic highway conditions.
“This therefore presents a risk to the users of the pedestrian crossing and other vehicles using the immediate road network.”
The inspector said that factors relating to various economic and social benefits put forward by the appellant could not be taken in account either for or against an advertisement consent proposal.