8.1 Photosensor Definition Table

The photosensor definition table on the bottom left of the screen defines photosensor scenarios for further analysis. The photosensor scenarios listed in the table are shown graphically on the 3-D isometric of the space in the upper left corner and on a reflected ceiling plan in the upper right corner. One photocell must exist for each electric lighting zone but more can be added for further testing in the analysis portion of the program. To add a photosensor, simply type the name and mounting information into the next blank row in the table. To remove a photosensor, delete all the photosensor information from the row. Blank rows in the middle of this table are acceptable and will be removed upon going to the next screen. The inputs for each column in the Photosensor definition table are as follows:

Photosensor Name – This field defines a name for the photosensor scenario defined on the corresponding line. This can be any name that makes sense to the user, although no blank spaces are allowed in the name. Use an underscore if a space in the name is desired. When a correlation calculation is performed, default position information will be automatically entered in the table for the zone number that corresponds to the end of the photosensor name. If the photosensor name does not end in an electric lighting zone number then default position information will be entered for the first lighting zone. In other words, end the photosensor name with the corresponding zone number if you want the default position information to be correct.

Photocell Type – This field is specified with a pull-down menu showing the current list of defined photocell types. SPOT contains a library of the following generic and measured photocell types:

• Cosine – This is a perfectly hemispherical distribution that gives a signal that is linear to photometric illuminance. Many photosensor products on the market attempt to achieve this type of spatial distribution response.
• 45°, 55°, and 65° Cosine – These spatial distributions are the same as the cosine distribution, but limited in overall scope to a cone with the specified angle. These sensors respond to a cone of luminance centered on the axis line of the sensor.
• TWS-1 – This is an older sensor distribution from The Watt Stopper with a fairly narrow band of distribution. It is no longer in production.
• Product Specific Sensors – The Lighting Research Center (LRC) released a Photosensor Specifiers Report under the NLPIP in 2007 which contains background information on daylighting controls and the current state of photosensor products. The report also presents measured spatial, spectral and control response algorithms for a sampling of currently used products, see the example spectral and spatial sensitivities to the right. The spatial responses of the selected photocells are modeled in the correlation calculations and the final annual calculations. The SPOT photocell and controller library is not exhaustive but gives options for representing most products currently available.
  

Mounting – This field sets the general mounting location for the photosensor. The user can choose from a list of mounting locations. Some photocell types only allow for closed loop (interior) scenarios. In these cases, only ceiling and free mounting options will be available in the drop down list. The following mounting locations are allowed:

• Ceiling – A ceiling mount is the default mounting location and is designated by entering a “C” into this field.
• South (S), East (E), North (N), West (W) – An “S”, “E”, “N”, or “W” designates a wall mounting on either the south, east, north, or west wall, respectively.
• Free (F) – A free-standing mount can be used to place the photosensor someplace other than the ceiling or walls of the space. This may be useful for placing photosensors beneath luminaries or on top of furniture systems.
  

Photocell Position Vectors – The three adjacent position fields define the location, aiming and rotation of the sensor for the current treatment zone using vector notation. The X values for each vector (1st number) represent the E-W dimension of the space. The Y values (2nd number) represent the N-S dimension of the space. The Z values represent the height component. The vectors must be entered with a comma separating the X, Y, Z values. The vectors do not have to be unitized. In the Reflected Ceiling Plan diagram, the photocells will be represented by three symbols ( ). The black asterisk indicates the Photocell Location, the red diamond indicates the direction the Photocell Aiming, and the red asterisk indicates the Photocell Rotation.

Photocell Location – The location vector gives mounting coordinates. The user will have to ensure the sensor does not get placed within a wall, overhang, or lightshelf element as this will result in inaccurate results.

Photocell Aiming – The aiming of the sensor gives the direction in which the photocell is looking. The default is down for ceiling mounted sensors.

Photocell Rotation – The rotation of the sensor indicates the direction in which the prominent sensor housing feature will face. The default is local building north for ceiling mounted sensors.