Photo-degradation of a biological sample

[alemns]

What the group thoughts are in relation to an experiment in which 520 nm monochromatic light will strike a biological sample, which it is not flat (most like resembling an arc) and can photo-bleach over time. Would irradiance (mW/cm2) or dose (mJ/cm2) be more appropriate to carry on studies on photo-induced degradation of the sample over time?

 

[Baluncore]

We see 520 nm as green, (at the blue end), daylight, near the peak of our vision.

The geometry of the source of 520 nm radiation, and whether the “arc” is a concave or a convex surface, may make a difference.

Total dose would be more relevant, since the sample accumulates joules and damage over time.
One watt is one joule per second.

 

[alemns]

thank you.

light source it is going to be incoherent, from LED(s). Target surface receiving illumination is approximately concave in shape.

any references by chance, discussing the physics (papers or textbook)...

irradiance integrated over time isn't dose?

 

[Baluncore]

irradiance integrated over time isn't dose?

The damage will be proportional to the dose, which is the integral of the irradiance, over time.
Dose (mJ/cm2) = exposure_time (seconds) * irradiance (mW/cm2);

 

[sophiecentaur]

Would irradiance (mW/cm2) or dose (mJ/cm2) be more appropriate to carry on studies on photo-induced degradation of the sample over time?

I guess there have been assumptions about the actual experimental conditions and the chemistry of the surface.

The information in the OP is a bit sparse. the thermal effect would depend on the Mean Power over a period that's dependent on the actual nature of the surface.

If the potential damage relates to peaks of temperature then you'd need to know what temperature the surface could reach. What is the thermal Conductivity of the material? If the 'material' is 'alive' then we can't make any reliable predictions. Some living cells are very dependent on peaks of incident energy. (Consider the damage from exposure to sunlight.) This may or may not be relevant, of course but it would affect which of the quantities should be measured.

If the whole exercise is about damage related to illumination in general then perhaps both total (or medium term mean) and peak (short term) Energy should be studied. The experiment would reveal which is the important one.