Design Method for Spectrally Enhanced Lighting

Spectrally enhanced lighting (SEL) is an effective way to reduce energy usage. The design method found on this page will help to implement SEL. For best results, be sure to hire a professional lighting designer familiar with designing successful SEL systems.

The 2004 Feasibility Study and 2006 Economics Study validated the effectiveness of the design method for spectrally enhanced lighting. The following three-step process describes the basis of the SEL design method.

Design Step 1: Determine Target Illumination Level

Determine the target illuminance and chart onto VEE/E slope for the presumed lamp type* (in this case, a 735 lamp). This determines the control point and defines the Visual Effectiveness target.

Graph 1: Image of a line graph entitled 'Visual Effectiveness Method for Determining Light Level Adjustment on the Basis of Equal Visual Acuity.' The y-axis is labeled 'Equivalent Visual Effective Illuminance - Visual Acuity, Paper Reading Task.' The x-axis is labeled 'Photopic Illuminance.' The top sloping line of the graph illustrates the Equivalent Visual Effective Illuminence at different points of Photopic Illuminance for an 850 lamp. This line starts at the origin and ends at roughly the coordinate of 60 Photopic Illuminance and 98 Equivalent Visual Effective Illuminance. The bottom sloping line of the graph illustrates the Equivalent Visual Effective Illuminence at different points of Photopic Illuminance for a 735 lamp. This line starts at the origin and ends at roughly the coordinate of 60 Photopic Illuminance and 72 Equivalent Visual Effective Illuminance. An upward vertical arrow is drawn from the 40 point on the Photopic Illuminance x-axis to where it intersects with the 735 lamp line at roughly 50 Equivalent Visual Effective Illuminance.

Visual Effectiveness Method for Determining Light Level Adjustment on the Basis of Equal Visual Acuity. Design Step 1: Determine target illumination level

* Using the formula P(S/P).78, where P = Photopic Illuminance, and S/P is the S/P value for the lamp as provided by the manufacturer.

Design Step 2: Use Equivalent Visual Illuminance as Control

Move along the Visual Effectiveness line to the VEE/E slope of the proposed new high correlated color temperature (CCT) light source (in this case, an 850 lamp). This ensures that the new lighting will provide equal visual acuity for paper reading tasks.

Graph 2: This is the same graph as described in Graph 1. Additionally, this graph has a horizontal arrow drawn from the 40 Photopic Illuminance point on the 735 lamp line to intersect with the 850 lamp line.

Visual Effectiveness Method for Determining Light Level Adjustment on the Basis of Equal Visual Acuity. Design Step 2: Use Equivalent Visual Illuminance as Control

Design Step 3: Assess New Photopic Level and Energy Reductions

The new photopic illuminance is determined as the point where the Visual Effectiveness value intersects the VEE/E slope of the new light source. This new photopic illuminance is used to determine energy savings using traditional photopic efficacy ratings (i.e., lumens per watt).

Graph 3: This is the same graph as described in Graph 2. Additionally, this graph has a downward arrow drawn from the 850 lamp line to the 30 point on the Photopic Illuminance x-axis. In this step, you are assessing the new photopic level and energy reductions. This graph illustrates that the 850 lamp light provides the same Equivalent Visual Effective Illuminance at a lower Photopic Illuminance rate than the 735 lamp light.

Visual Effectiveness Method for Determining Light Level Adjustment on the Basis of Equal Visual Acuity. Design Step 3: Assess New Photopic Level & Energy Reductions