EN 14500-2008 pdf download.Blinds and shutters Thermal and visual comfort – Test and calculation methods.
6.2.3.2 Integrating sphere
An Integrating (or Ulbricht) sphere is a hollow sphere whose internal surface is a diffuse white reflector. This optical device is used to collect flux either reflected or transmitted from a sample or to provide isotropic irradiation of a sample from a complete hemisphere. The hollow sphere has apertures for admitting and detecting flux arid usually having additional apertures over which sample and reference specimen are placed.
An integrating sphere equipped with a radiometer, photometer and/or spectroradiometer is recommended for the measurement of:
direct-hemispherical reflectance and transmittance,
— diffuse reflectance and transmittance.
The direct-direct components can then be obtained by subtracting one from the other.
NOTE 1 Special care has to be taken when the transmittance/reflectance of thick translucent samples (e.g. gLass slats with printed patterns) is measured, because of possible lateral losses of transmitted/reflected light.
NOTE 2 Integrating spheres are not suitable for measuring luminescent materials.
NOTE 3 The higher the reflectance of the sphere coating , the higher is the sensitivity of the detection equipment.
NOTE 4 Common materials for sphere coatings are BaSO4 and pressed and low-density sintered PTFE.
NOTE 5 The basic idea behind integrating spheres is that the indirect illuminanceiirradiance of the inner sphere wall is assumed to be proportional to the flux transmitted/reflected by the test specimen or reference sample. This is true for spheres with perfectly isotropic diffuse reflecting walls without openings. The llluminancelirradiance of directly irradiated parts of the sphere is not proportional to the flux. It is therefore necessary to equip the sphere with baffles as it is described in Clause 6.2.3.3.
6.2.3.3 Requirements
An integrating sphere together with the detectors shall fulfil the following requirements:
— All detector ports shall be equipped with additional baffle(s) In order to cut the line of sight between sample/reference port and detector(s). This ensures that the detector is not illuminated directly. The baffles shall be coated with a diffuse, spectrally non-selective coating with a very high reflectance (normal-hemispherical spectral reflectance > 92 %).
— Detectors shall either be:
Radiometers/photometers which are sensitive to light coming from all the different possible directions in the integrating sphere. Radiometers/photometers shall evaluate the incoming radiation according to the cosine law;
6.2.4 Reference samples
The reference samples shall be of sufficient size to prevent the possibility of light leakage at the edges of the entrance port. The size shall be compatible with the sample compartment of the instrument. Reference samples shall be clean and dry. The storage and the cleaning procedures stated by the manufacturer shall be followed.
Reference samples should have similar reflectance or transmittance properties as the test samples (e.g. diffuse reflecting reference sample for diffusely reflecting test sample). With the measurement of reference samples the following accuracies shall be proven:
Diffuse reflecting reference samples (e.g. low-density sintered PTFE) with a reflectance between 0,85 and I shall be measured with an absolute accuracy of less or equal than 0,04:
— Specularly reflecting reference samples (mirrors) with a reflectance between 0,85 and 1 shall be measured with an absolute accuracy of less or equal than 0,03;
— Directly transmitting reference samples (e.g. glass sheets) with a transmittance between 0,75 and 1 shall be measured with an absolute accuracy of less or equal than 0,03.
Secondary reference samples calibrated by the laboratory itself are allowed, when the additional uncertainty is taken into account and when the accuracy Is traceable.
6.3 Test samples
6.3.1 General
The test samples shall be of sufficient size to prevent the possibility of light leakage at the edges of the entrance port The size shall be compatible with the sample compartment of the instrument. Test samples shall be clean and dry, unless otherwise specified. The storage and the cleaning procedures stated by the manufacturer shall be followed.
Test samples shall fulfil the following additional requirements:
— The irradiation equipment must be able to irradiate the sample according to the requirements stated in Clause 6.2.2;
— The detection equipment must be able to detect the total transmitted/reflected flux according to the requirements stated in Clause 6.2.3.
If these requirements are not fufiIled, the sample can not be tested with the test equipment under consideration.EN 14500-2008 pdf download.