Understanding Photometric Data in Interior Environment Design

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Photometric data is crucial in interior environment design as it deals with the measurement of light emitted from fixtures. This data includes luminous flux, luminous intensity, luminance, and illuminance. Candle power distribution curves provide insight into the direction and intensity of light from luminaires, aiding in identifying potential glare and hot spot issues. By grasping the basics of photometry, designers can optimize lighting systems for efficiency and visual comfort.

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ART 2640, Building Systems of Interior Environments Fall Semester 2020 Tuesdays & Thursdays 10:30-11:50 Online Matthew Ziff, Associate Professor M. Arch, Architect, NCIDQ Office: W 325 Grover Center E-mail: ziff@ohio.edu Photometric Data Explained

Photometric Data Photometry is the science of the 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

Photometry is the science of measurement of light. There are 4 basic quantities that are measured: Luminous flux (F) measured in Lumens: is the measure of the total power of light emitted, at all wavelengths in the visible band. The SI unit of luminous flux is the lumen (lm). Luminous intensity (I) is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle. The SI unit of luminous intensity is the candela (cd).

Luminance (L) is the luminous intensity of a surface in the direction of the observer. The luminance indicates how much luminous flux will be perceived by an eye looking at the surface from a particular angle of view. Luminance is measured in candela per square meter (cd/m ). Illuminance (E) or Foot Candle, is the luminous flux measured on the surface receiving the light, per unit area. Its unit of measurement is the lux/foot candle.

Photometric Data Photometric Data may include the following information: Candle Power Distribution Curve Luminaire Efficiency Coefficient of Utilization Spacing Criterion Physical Dimensions Lamp and Ballast Data Efficacy of fixture and of lamp

Photometric Data Candle Power Distribution Curve Describes the direction and the intensity of light from the luminaire. Candle power is the measure of light output at the source. 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. Candle Power Distribution Curve Explained One example of candle power distribution curve

Photometric Data Candle Power Distribution Curve: Vertical View (ceiling mounted light fixture) Batwing Distribution (Good for Computers)

Photometric Data Candle Power Distribution Curve: ceiling suspended light fixture Even Distribution

Photometric Data Candle Power Distribution Curve: ceiling suspended light fixture 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 Data Luminaire 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.

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

Photometric Data 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.) Room Ratios the larger the number the larger the room.

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 Data Spacing 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 Data Spacing 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.) 7-2 MAX 6-0 MAX

Photometric Data Physical Dimensions and Finishes

Photometric Data Lamp and Ballast Data

Photometric Data Manufacture 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