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Most of the way through safety calculations
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wandell committed Mar 29, 2020
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290 changes: 222 additions & 68 deletions human/humanUVSafety.m
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function exposureMinutes = humanUVSafety(irradiance,wave)
function [val, level] = humanUVSafety(energy,wave,varargin)
% Calculate the UV hazard safety for an irradiance
%
% Synopsis
% exposureMinutes = humanUVSafety(irradiance,wave)
%
% [val, level] = humanUVSafety(irradiance,wave,varargin)
%
% Inputs:
% irradiance - in energy (watts/nm/m2)
% wave - wavelength samples of the irradiance
% energy - irradiance (skineye, eye) or radiance (bluehazard) (watts/nm/m2)
% wave - wavelength samples of the irradiance
%
% Optional key/val pairs
% method - 'skineye' or 'eye' (sections 4.3.1 and 4.3.2 of the PDF)
% duration - Stimulus duration in seconds used for 'eye' and 'bluehazard'
% methods
%
% Return:
%
% Returns
% exposureMinutes - Maximum safe exposure time (minutes) per eight hour
% period
% Method: 'skineye'
% val - Maximum safe exposure time (minutes) per eight hour period
% level - hazardEnergy
%
% Method: 'eye'
% val - logical (true/false)
% level - the irradiance integrated over wavelength
%
% Method: 'bluehazard'
% val - logical (true/false)
% level - the dot product of the radiance with the blueLightHazard
% function.
%
% Description:
%
% (Near UV is also called UV-A and is 315-400nm)
%
% We caclulate for a constant light (not time-varying).
%
% The data for the Actinic safety function curves were taken from this
% paper
%
% IEC 62471:2006 Photobiological Safety of Lamps and Lamp Systems. n.d.
% Accessed October 5, 2019. https://webstore.iec.ch/publication/7076
% Accessed October 5, 2019. https://webstore.iec.ch/publication/7076
% J.E. Farrell has a copy of this standard
%
% Notes: Near UV is also called UV-A and is 315-400nm.
% Google Drive:
% https://drive.google.com/file/d/1JQC_R7QDGd58vpNByyKvrVlwEfTk5-Uu/view?usp=sharing
%
% The document explains the different functions in these sections.
%
% Actinic UV hazard exposure limit skin and eye (4.3.1)
% Near UV hazard limit for the eye (4.3.2)
% Retinal blue light hazard exposure (4.3.3)
% Retinal blue light small source (4.3.4)
% Retinal thermal hazard (4.3.5)
% Retinal theermal hazard for weak visual stimulus (4.3.6)
% Infrared exposure for the eye (4.3.7)
% Thermal hazard for the skin (4.3.8)
%
% Notes
%
% I was not sure if radiance -> irradiance is multiplied by 2pi or 1pi.
% So, we checked with Peter and the Internet. The answer: 1pi.
%
% From: Peter B. Catrysse <[email protected]>
% Sent: Wednesday, August 21, 2019 11:02 AM
% To: Joyce Eileen Farrell <[email protected]>
% Subject: RE: spectroradiometric measurements
%
% Hello Joyce,
%
% It is definitely pi.
% There is 2*pi solid angle for the hemisphere, but when you integrate
% you end up getting pi as factor.
%
% See you next week,
%
% Peter
%
% From: Joyce Eileen Farrell [mailto:[email protected]]
% Sent: Tuesday, August 20, 2019 10:58 PM
% To: Peter Bert Catrysse <[email protected]>
% Subject: Re: spectroradiometric measurements
%
% Hi Peter,
%
% Thanks so very much for giving me the conversion from radiance to
% irradiance.
%
% is it
% E = pi*L/R (where E is irradiance, L is radiance and R is reflectance)
% or
% E=2pi*L/R
%
% ----
%
% See also this exchange online
%
% https://physics.stackexchange.com/questions/116596/convert-units-for-spectral-irradiance
%
% The person multiplies b6000 by pi, not 2pi
%
% Notes
%
% This calculation is for skin and eye (4.3.1).
%
% We are calculating the irradiance, not the irradiance at the retina. We
% could try to calculate irradiance at the retina, accounting for the pupil
% diameter and the tranmissivity of the lens. But the standard's committee
% baked that into the standard itself. (page 27).
%
% A related issue is the area subtended. In our case we are measuring
% irradiance as watts/m2, so the assumption is that any area is accounted
% for by the units, and that over the area that is illuminated by the light
% the intensity is uniform.
%
% See also
% s_humanSafetyUVExposure

%% Near-UV hazard exposure limit
%{
This calculation has no weighting function.
For times less than 1000 sec, add up the total irradiance
from 315-400 without any hazard function (Equation 4.3a). Call this E_UVA.
Multiply by time (seconds). The product should be less than 10,000.
For times exceeding 1000 sec, add up the total irradiance, divide by the
time, and the value must be less than 10 (Equation 4.3b).
% s_humanSafetyUVExposure, ieLuminance2Radiance
%

%}

%% Check inputs

if ieNotDefined('irradiance'), error('Spectral irradiance required'); end
if ieNotDefined('wave') || length(wave) ~= length(irradiance)
error('wave representation missing or incorrect');
end
varargin = ieParamFormat(varargin);

%% Load the standard function
p = inputParser;

fname = which('Actinic.mat');
Actinic = ieReadSpectra(fname,wave);
% semilogy(wave,Actinic); xlabel('Wave'); grid on;
p.addRequired('irradiance',@isvector);
p.addRequired('wave',@isvector)
p.addParameter('method','skineye',@(x)(ismember(ieParamFormat(x),{'skineye','eye','bluehazard'})));
p.addParameter('duration',1,@isnumeric); % Used for 'eye' method only
p.parse(energy,wave,varargin{:});

%% The UV hazard safety formula
%
% sum (Actinic(lambda,t) irradiance(Lambda)) dLambda dTime
%
% Our stimuli are constant over time, so this simplifies to
%
% T * sum(Actinic(lambda) irradiance(lambda) dLambda
%
% where T is the total time. For simplicty we set T = 1, so we are
% calculating the total amount of time (in minutes) for a light with this
% spectral irradiance.
%
% Follow the units this way:
%
% Irradiance units: Watts/m2/nm
% Watts = Joules/sec
%
% Watts/m2/nm * (nm * sec) % Irradiance summed over nm and time
% Joules/sec/m2/nm * (nm * sec)
% Joules/m2 % Becomes Joules/area
%
method = ieParamFormat(p.Results.method);
duration = p.Results.duration;

%% Set up wavelength sampling

% Summing over wavelength and time (1 sec)
if numel(wave) == 1
dLambda = 10;
disp('Assuming 10 nm bandwidth');
else
dLambda = wave(2) - wave(1);
end
hazardEnergy = (dot(Actinic,irradiance) * dLambda);

% This is the formula from the standard to compute the maximum daily
% allowable exposure from the hazard energy.
%{
The maximum permissible exposure time per 8 hours for ultraviolet
radiation incident upon the unprotected eye or skin shall be computed by:

t_max = 30/E_s (seconds) (Equation 4.2)
%% Load the standard function
switch method
case 'skineye'
fname = which('Actinic.mat');
Actinic = ieReadSpectra(fname,wave);
% semilogy(wave,Actinic); xlabel('Wave'); grid on;

%% The UV hazard safety formula
%
% sum (Actinic(lambda,t) irradiance(Lambda)) dLambda dTime
%
% Our stimuli are constant over time, so this simplifies to
%
% T * sum(Actinic(lambda) irradiance(lambda) dLambda
%
% where T is the total time. For simplicty we set T = 1, so we are
% calculating the total amount of time (in minutes) for a light with this
% spectral irradiance.
%
% Follow the units this way:
%
% Irradiance units: Watts/m2/nm
% Watts = Joules/sec
%
% Watts/m2/nm * (nm * sec) % Irradiance summed over nm and time
% Joules/sec/m2/nm * (nm * sec)
% Joules/m2 % Becomes Joules/area
%
% This standard is defined for 200-400 nm, but we do not have any
% data that go that short.

% We only evaluate up to a wavelength limit of 400nm
wLimit = (wave <= 400);
hazardEnergy = (dot(Actinic(wLimit),energy(wLimit)) * dLambda);

% This is the formula from the standard to compute the maximum daily
% allowable exposure from the hazard energy.
%{
The maximum permissible exposure time per 8 hours for ultraviolet
radiation incident upon the unprotected eye or skin shall be computed by:
E_s is the effective ultraviolet irradiance (W/m^2). The formula for
E_s is defined in Equation 4.1. It is the inner product of the Actinic
function and the irradiance function, accounting for time and
wavelength sampling.
%}
t_max = 30/E_s (seconds) (Equation 4.2)
% We return the time in minutes.
exposureMinutes = (30/hazardEnergy)/60;
E_s is the effective ultraviolet irradiance (W/m^2). The formula for
E_s is defined in Equation 4.1. It is the inner product of the Actinic
function and the irradiance function, accounting for time and
wavelength sampling.
%}

% We return the time in minutes.
val = (30/hazardEnergy)/60;
level = hazardEnergy;

case 'eye'
%% The calculation in 4.3.2 is specialized for the eye.
%
% The formula they derive in that case is a maximum irradiance value that
% is calculated separately when the eye is exposed for less than 1,000 sec
% or more than 1,000 seconds.
%
% Suppose for an irradiance level that is constant over time we have
%
% IR = Integral (E(lambda) dlambda) (Watts/m2)
%
% where E(lambda) has units of Watts/nm/m2
%
% ExpTime * IR has units of (sec * Watts/m2 = Joules/m^2)
%
% Then for times less than 1000 sec, the rule is
%
% ExpTime * IR < 10,000
%
% For times greater than 1000 sec we require that
%
% IR < 10
%
wLimit = (wave <= 400);
level = dLambda * sum(energy(wLimit));

% val is set to true for safe and false for not safe
val = false;
if duration <= 1000 % seconds
if level*duration < 10000, val = true; end
elseif level < 10 % Duration is long, so level must be low
val = true;
end
case 'bluehazard'
% Retinal blue light hazard, Section 4.3.3
%
% Potential for a photochemically induced retinal injury
% resulting from radiation exposure at wavelengths primarily
% between 400 nm and 500 nm. This damage mechanism dominates
% over the thermal damage mechanism for times exceeding 10
% seconds. (Page 15).
%
% The standard applies over the wavelength range from 300-700 nm.
%
fname = which('blueLightHazard.mat');
blueHazard = ieReadSpectra(fname,wave);
% ieNewGraphWin; plot(wave,blueHazard)

level = dLambda*dot(blueHazard,energy);

% Equations 4.5a, 4.5b
val = false;
if duration <= 1e4 % seconds
if level*duration < 1e6, val = true; end
elseif level < 1e2 % Duration is long, so level must be low
val = true;
end

otherwise
error('Unknown UV safety method %s\n',method);
end

end
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