Luminous efficacy of pure blackbody radiation as a function of temperature. The effective temperatures of a typical incandescent filament and the solar surface are marked by stars, corresponding to 15 and 93 lm/W, respectively.
The photopic sensitivity curve is shown as the solid curve. Blackbodies corresponding to 5800 K (dashed) and 2800 K (dashed-dotted), normalized to the same total radiant flux, are shown for reference. Dotted vertical lines represent different bounds within which we consider artificial ideal white light sources, corresponding to photopic curve intercepts at 0.5%, 1%, 2%, and 5% sensitivity levels.
Luminous efficacy of ideal, truncated sources for four different wavelength ranges as a function of blackbody temperature. The four wavelength ranges corresponding to 0.5%, 1%, 2%, and 5% sensitivity thresholds of the photopic response curve, whose wavelengths are indicated by vertical dotted lines in Fig. 2. Stars mark the efficacies at 5800 K.
Maximum luminous efficacy achievable as a function of photopic sensitivity threshold (a) and the corresponding color temperature (b).
Conditions for maximum luminous efficacy for a truncated blackbody at 5800 K, allowing asymmetric red and blue cutoff wavelengths. Panel (a) shows the maximum luminous efficacy (solid) and associated Planckian offset (dashed) as a function of CRI achieved. The star marks the point at which the Planckian offset reaches and is no longer considered to be “white.” Panel (b) shows the wavelength cutoffs (solid curves) that maximize , and their corresponding photopic cutoff sensitivities (dashed for blue, dotted for red). Numbers correspond to the stars, which themselves indicate the point at which the Planckian offset reaches .
Conditions for maximum luminous efficacy for a truncated blackbody at 2800 K, allowing asymmetric red and blue cutoff wavelengths. Conventions follow those from Fig. 5.
16 W CFL (“60 W” replacement) at turn-on (a) and after warm-up (b). The spectral luminous efficacy, correlated color temperature, Planckian offset, and color rendering index are displayed for each spectrum. The photopic sensitivity curve is also displayed for reference.
1.5 W LED lights labeled as having color temperatures of 3000 K (a) and 6500 K (b). The measured color temperature of the light in (b) is clearly a poor match to that indicated on the packaging. Conventions and labels follow that of Fig. 7.
Backlighting for laptop computer liquid crystal displays, showing fluorescent tube illumination (a) and LED illumination (b). Conventions and labels follow that of Fig. 7.
Properties of truncated continuum sources.
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