The ILT 350 is a portable, handheld spectroradiometer that is configured for measuring the illuminance in lux and colour properties (CIE chromaticity, CCT and colour rendering) of lamps, LEDs and other light sources. Whilst technically a spectroradiometer, we categorise the ILT 350 as a “photometer” as it provides spectroradiometric accuracy and capabilities for less than the cost of a traditional tristimulus colorimeter.
The ILT 350 is a portable, handheld spectroradiometer that is configured for measuring the illuminance in lux and colour properties (CIE chromaticity, CCT and colour rendering) of lamps, LEDs and light sources. Whilst technically a spectroradiometer, we categorise the ILT 350 as a “photometer” as it provides spectroradiometric accuracy and capabilities for less than the cost of a traditional tristimulus colorimeter.
Being a spectroradiometer ensures that the ILT 350 gives accurate readings with any type of light source. Measure spectral irradiance (Watts/m2, 380-780nm), the illuminance (lux), the correlated colour temperature of white light sources (CCT, Kelvin), the CIE chromaticity (xy or u’v’), the dominant wavelength of coloured light sources (nm) and the CIE colour rendering index, CRI (Ra, R1-15).
The ILT350 is a great choice for those requiring an affordable, simple to use yet accurate meter for measuring both the illuminance and colour / colour rendering properties of their light sources. Of note is the NIST traceable, ISO 17025 accredited calibration.
The device comes with an integrated 12mm diameter cosine correcting receptor with magnetic protective cover. It features three measurement speeds to cope with varying levels of illumination, including fast (0.5 seconds), slow (2.5 seconds) and an automatic mode (0.5 – 27 seconds). Data is provided in 1nm increments. The spectral bandwidth of the spectrometer is approximately 2.5nm (FWHM) with +/- 0.3 nm wavelength accuracy.
The internal memory can store up to 100 datasets and you can export data into Excel file formats.
Key Features:
Meter Type | Portable Irradiance Spectroradiometer |
Spectral Response | 380-780nm |
Sensor Type | Sony linear CCD with 12mm cosine corrected input |
Spectroradiometric Measurements | Watts per square meter per nm (W/m2.nm) |
| PPFD/PAR |
Photometric Measurements | Illuminance (lux) |
Colorimetric Measurements | CIE chromaticity (xy, uv, u’v’) |
| Correlated colour temperature (CCT, Kelvin) & Duv |
| Dominant wavelength (nm) & purity (%) |
| CIE tristimulus values (XYZ) |
| CIE colour rendering (Ra, R1-14) |
Range (illuminance) | 20 to 100,000 lux |
Calibration | NIST traceable, ISO 17025 accredited |
Spectral Resolution | 2.5nm FWHM |
Wavelength Accuracy | ± 0.3nm |
Interface | USB 2.0 Mini |
On-board Data Storage | Up to 100 datasets |
Power Supply | USB powered, internal Lithium ion battery |
| Up to 6 hours operation between charges |
Dimensions | 160 x 75 x 43mm (L x W x D) |
Weight | 0.26kg |
Operating Temperature | 0-40°C ambient |
The ILT 350 is a spectroradiometer. Other types of light meter are radiometers, photometers, colorimeters and spectrometers, which all measure the amount of light but they operate in fundamentally different ways and have advantages and disadvantages.
Radiometers, Photometers & Colorimeters
Radiometers and photometers consist of a photodetector, an electrical readout and a calibration. The spectral response of a photodiode varies with the wavelength of the incident radiation. This means that 1 W/m2 of irradiance at 350nm in the UV will produce a different electrical current compared to 1 W/m2 of red light at 650nm.
The photodetector would typically be fitted with an optical filter which modifies the inherent spectral response of the sensor. For a radiometer to measure the amount of monochromatic light, you only need to know the calibrated spectral response of the photodiode at the relevant wavelengths. If the light source is anything other than monochromatic (which is the case for all light sources except lasers), a radiometer with bare photodiode cannot yield absolute radiometric measurements. A “radiometric” filter can be fitted to the photodiode that normalises the response over a limited wavelength range, typically ±10% from 450-950nm, which provides a partial solution.
A radiometer can also be equipped with a filter that limits or adapts the spectral response and these are typically used in safety or medical applications where certain wavelengths are more dangerous or more efficacious than others. Examples of this are measuring the safety of UVC light sources, measuring the erythemal effectiveness of a UVB source and measuring blue phototherapy lights used for the treatment of bilirubin (jaundice in new-born babies).
A photometer is similar to a radiometer, but the photodiode is equipped with a special filter that modifies the spectral sensitivity of the detector/filter combination so as to match as closely as possible that of the human vision system, defined at the CIE spectral luminous efficiency for photopic vision (“photopic” response). The photopic response of the human eye strongly favours green coloured light, with blue and red light being perceived as less intense. Thus, a photopic sensor ranks the brightness of light sources in close agreement to how the human vision system would perceive them.
A colorimeter is a type of photometer that combines three of four photodiodes each with a filter that closely matches the tristimulus response of the eye (the XYZ or XRXBYZ tristimulus colour matching functions). A colorimeter measures the emitted colour of the light source under test, and reports this as tristimulus values, as CIE chromaticity coordinates and as correlated colour temperature (CCT) values or as a dominant wavelength. The Y filter of a colorimeter is the same as the photopic filter in a photometer, hence a “tristimulus” colorimeter can also function as a photometer.
Spectrometers & Spectroradiometers
Whereas radiometers, photometers and colorimeters employ photodiodes with special filters, a spectroradiometer measures what is called the spectral power of the light source, which is the amount of light at each wavelength. The spectral response of the spectroradiometer is calibrated at each wavelength, which therefore avoids the error that arises from measuring the irradiance of broadband light sources with unfiltered radiometers (or even radiometers equipped with normalising filters).
From the measured spectral power, the desired radiometric, photometric or colorimetric metrics can be calculated. A spectroradiometer avoids the potentially significant errors that filtered photometers and colorimeters suffer from where the spectral response of the filtered sensor doesn’t exactly match that of the target observer, for example the photopic response of the eye. This is an important consideration; a high-quality photometer may have a average spectral mismatch (the f1’ factor) to the photopic observer of 5% over the 380-780nm visible light band, but can still yield errors of 50% or more when used to measure blue or red LEDs, for example.
A spectroradiometer is the name given to a spectrometer that is equipped with appropriate collection optics and an absolute calibration. A spectrometer is an optical instrument that employs a diffraction grating that physically separates the incident light into its component wavelengths. Each discrete wavelength is imaged onto an array photodetector, which allows for the recording of a spectral power distribution instantaneously.
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