Summary of Key Findings in Rensselaer Tech Study of Sign Visibility, Conspicuity and Legibility

The academic paper entitled Factors Affecting Sign Visibility, Conspicuity and Legibility: Review and Annotated Bibliography originally appeared in the June 2017 issue of “The Interdisciplinary Journal of Signage and Wayfinding,” an academic, peer-reviewed publication published twice a year by the Academic Advisory Council for Signage Research and Education (AACSRE). The following are a few, salient points in the paper which pertain to sign conspicuity and correspond directly to electric sign luminance:

  • Among the photometric properties of signs most related to conspicuity is the sign luminance.
  • Not surprisingly, higher sign luminances tend to make highway signs easier to detect at night (Forbes et al. 1967).
  • Internally-illuminated and neon commercial signs provide superior legibility to externally-illuminated signs (Kuhn et al., 1998 and Garvey & Kuhn, 2011)

The paper also cites a 1967 research study, “Luminance Requirements for Illuminated Signs” by Dyer, Smith and Janson (Highway Research Record 167: 16-37) which recommends a luminance range of 700-1,700 candelas per square meter (nits) for urban locations having bright ambient lighting.

In this vein, it’s crucial to understand that ordinary illuminated signs do not incorporate brightness controls, but are manufactured to provide adequate luminance in a wide range of nighttime conditions and outdoor locations. Furthermore, modern laboratory testing of new signs manufactured according to established industry practices confirms that illuminated signs generally do not exceed the range recommended in the Dyer, Smith and Janson study.

The conventional recommendation for electric-sign luminance cited by the Illuminating Engineering Society (IES) “Lighting Handbook”  is 700-1,000 candelas per square meter. Modern lab tests indicate that the luminance typical of most new electric signs does not exceed the bottom of the IES-recommended range (i.e. 700 candelas per square meter). Existing, outdoor signs tend to be less bright due to the impact of aging and environmental exposure.

Efforts by regulatory bodies to limit electric-sign luminance thus constitute unnecessary tampering with the long-established, operational properties of illuminated signs. Such efforts typically are based on the following false assumptions:

  1. That signs are brighter than necessary.
  2. That sign manufacturers have gradually increased the luminance of their products over time

The Rensselaer Tech article can be accessed in its entirety at




Bill Dundas

Bill Dundas

Bill Dundas, a 40-year veteran of the on-premise sign industry as a fabricator, installer and journalist, is President/Executive Director of the Foundation for the Advancement of the Sign Industry (FASI).

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