Photometric DataPhotometry is the science of measurement of light.

Photometric data is a set of information related to the amount of light emitted from individual fixtures.

Independent labs are used to verify and objectively report photometric data from fixture manufactures

Photometric DataPhotometric Data may include the following information:

Candle Power Distribution Curve

Luminaire Efficiency

Coefficient of Utilization

Spacing Criterion

Physical Dimensions

Lamp and Ballast Data

Efficacy

Photometric DataCandle Power Distribution Curve

Describes the direction and the intensity of light from the luminaire.

Candle power distribution curves can also help determine if the fixture may create problems with direct and reflected glare as well as problems with hot spots.

Photometric DataCandle Power Distribution Curve

‘Batwing’ Distribution (Good for Computers)

Photometric DataCandle Power Distribution Curve

‘Even’ Distribution

Photometric DataCandle Power Distribution Curve

Potential Problems:

Photometric Data

Indirect bat wing pattern may reduce hot spots (unacceptable bright areas) on the ceiling.

Semi Indirect with a bat wing pattern down to reduce potential of reflected glare.

Photometric DataLuminaire Efficiency describes the amount of light that is emitted from the luminaire compared to the amount of light that is generated by the lamps.

All fixtures absorb some of the light from the lamps. Comparing luminaire efficiencies between fixtures allow for quick energy efficiency ratings.

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Photometric DataCoefficient of Utilization (CU)

Coefficient of Utilization (CU) is the ratio of lumens on the work surface to the lumens emitted by the luminaire.

The CU is influenced by the reflectance values of materials, size and shape of the room, and the placement of the luminaire.

The CU is used in the lumen calculation method that is used to determine the light levels for ambient lighting systems.

Photometric DataHigh Coefficient of Utilization (CU) values means more light reached the work surface and is more efficient.

Photometric Data

Room Ratios the larger the

number the larger the

room.

Coefficient of Utilization (CU) Table

pcc = reflectance value of the ceiling.

pw = reflectance value of walls

Typically the chart assumes a 20% reflectance value for the floor. (This is due to typically dark colors and furnishings.)

Photometric Data Coefficient of Utilization (CU) Table

Note that small rooms with light colors have a high CU.

Large rooms that are dark have a low CU.

The CU represents the percentage of lumens that reach the work surface from the fixture.

Photometric DataSpacing Criteria describes the maximum acceptable distance between fixtures when they are laid out in a room. The number provided by the fixture manufacture is a ratio that is multiplied by the distance between the work plane that is to be illuminated and the bottom of the fixture.

Photometric DataSpacing Criteria

If the distance between the fixture and the work plane is 6 then the maximum spacing criteria would be 6X1.2 = 7.2 parallel to the fixture and 6X1=6 90 degrees to the fixture.

(Remember that these are the maximum spacing recommendations.)

6-0 MAX

7-2 MAX

Photometric Data Physical Dimensions and Finishes

Photometric DataLamp and Ballast Data

Photometric DataManufacture Photometric Data

Fluorescent with Wrap Around Prismatic Lens

Fluorescent with Prismatic Lens

Deep Cell Parabolic Fluorescent

Semi Indirect Fluorescent

Indirect Fluorescent

Compact Fluorescent Down Light

Incandescent Down Light

MR 16 Down Light

HID Down Light

Photometric DataManufacture Photometric Data

HID Down Light

Pendent Fixture

Wall Washer

Placement Guide

Calculation Data