LEDs certainly have their place in displays, message centres and giant TV screens, and as replacements for incandescent lamps in lighting applications.
Their use as an alternative to neon or Cold Cathode Lighting is less clear. Light output, efficacy and lifetimes can be compromised by inadequate design and installation.
The environmental conditions can actually preclude their use in extremes of temperature.
E.g. South facing installations in hot climates.
LEDs are point sources which have plenty of significant applications. When a linear source is required, such as in architectural lighting, then there is still nothing better than neon or Cold Cathode Lighting.
M. Hall. B.Sc., M.R.S.C.