Application of JETI Spectroradiometer specbos 1211UV

Evaluation of Hazardous Optical Radiation

The rapid progress in development of new bright light sources, mainly based on LEDs, turned the attention to the problem of damaging of the human eye and skin by non coherent light sources.
The hazardous effect of laser radiation to the human eye and skin is studied for a long time and several standards and by-laws regulate the handling. Today more and more attention is payed to the effect of incoherent optical radiation on the human body.

Read also the application note 26 ( 2.2 MB).

The main interactions are the following:
  • photobiological effect of the UV part of spectrum to eyes and skin
  • hazardous effect of blue part of spectrum to the human eye
  • thermal effect of red and IR part of spectrum to human skin

The European Union issued the directive 2006/ 25/ EC, which defines the obligations for employers to protect the employees against health injuries caused by incoherent optical radiation. This directive is currently transferred into national laws.

Additional documents related to the topic are:
  • AOR Guide 2006/25/EC (Explanation of the directive)
  • ANSI/ IESNA RP-27.1-96 and RP-27.2-00 (Recommended practice)
  • IEC 62471 (Photobiological safety of lamps and lamp systems)
  • CIE S007/ ISO 17166 (Erythema Reference Action Spectrum and Standard Erythema Dose)

The Technical committee TC 2-58 of CIE currently prepares a standard for the measurement of Luminance and Radiance of LEDs, taking particular account of the specific requirements of relevant photobiological safety standards.

 

The following tables shows the different measuring values of the directive 2006/ 25/ EC (the data of the ANSI publication are equal):

Irradiance based measuring values

Hazard name Symbol Wavelength range in nm Weighting function Remark
         
Ocular exposure EUVA 315 (320) – 400 - Different limits below and above 1000 s
IR radiation exposure EIR 780 – 3000 - Different limits below and above 1000 s
Skin thermal exposure EH 380 - 3000 - Limited to small skin areas
Skin and ocular exposure ES 200 - 400 S(λ)  
Retinal blue light exposure – small source EB 300 - 700 B(λ) in IESNA also aphatic (A(λ)), different limits below and above 100 s
 
 

Radiance based measuring values

Hazard name Symbol Wavelength range/ nm Weighting function Remark
         
IR radiation exposure – weak visual stimulus LIR 780 - 1400 R(λ) Subtended angle of source needed
Retinal thermal exposure LR 380 - 1400 R(λ) Subtended angle of source needed
Retinal blue light exposure LB 300 - 700 R(λ) in IESNA also aphatic (A(λ)), different limits below and above 1000 s
 

Some quantities are based on pure radiometric data, but the majority are calculated by weighting the source spectrum with special functions. The EU directive 2006/25/EC allows the calculation and/ or the radiation measurement to obtain the hazardous potential of a source. The radiometric results have to be transfered into exposure values using the real exposure times. Afterwards the results have to be compared with the limits of exposure for the different effects, defined in the standards. Vice versa is it possible to calculate the maximum exposure time for an employee in this radiation situation.

The measurement can be the more relyable choice, but it is necessary to use a suited measuring instrument. It can be carried out by filter instruments (detector with appropriate filter to obtain the defined sensitivity characteristics) or a spectroradiometer, where the weighting is done by calculation. The latter solution is the more flexible one, because the weighting functions can easily be changed by the software. The mentioned documents recommend the useage of a double monochromator system, but such instrument is not easily portable.

 

A more simple spectroradiometer can be used, if one has a good knowledge of the application and when the parameters of the instrument are carefully considered, especially the stray light, the wavelength accuracy, the viewing angle, the bandwidths, the specification of the input optics (homogeneity, polarization influence) and the noise limit (specified by the noise equivalent input).

 

The following figure shows the measurement of a welding arc by specbos 1211 UV as well as the weighting by the S(λ) and B(λ) curves. 

 

welding 300

welding graph
Measurement of a welding arc with specbos 1211UV (click to enlarge)
 

IESNA RP-27.2-00, IEC 62471 and ISO 17166 describe different measurement geometries for different kinds of hazard.

The radiance based measurements have to be done with a direct viewing optics (small viewing angle, radiance mode), the irradiance ones with an optics viewing in the half space (viewing angle 180° = 2π, measurement with diffusor or integrating sphere, irradiance mode). The exposure result will be obtained by integration of the weighted spectrum and multiplication by the exposure time (presumed that the intensity of the radiation is constant during the exposure).

hazard weight func

Weighting functions (click to enlarge)
 

The figure above shows the three weighting functions S(λ), B(λ) and R(λ), additionally the A(λ) function, which is only included in the US document ANSI/ IESNA RP-27.2-00.
The meaning of the functions is as follows:

  S(λ)  UV Hazard Weighting Function
   

Skin and eye injury caused by UV radiation

 
  B(λ)  Blue-light UV Hazard Weighting Function
   

Photochemically induced retinal injury induced by blue radiation

 
  R(λ) Burn Hazard Weighting Function
   

Thermal damage of the eye, especially of retina and lens

 
  A(λ) Aphakic Hazard Weighting Function
    Mainly retinal injury of the lensless eye
     

The software JETI LiVal includes the Hazard measurements in a special calculation window. It shows the limits of the different groups for the selected category, calculates the final measuring value and shows the classification into the risk groups.

hazard
Screenshot LiVal widget Hazard (click to enlarge)