How to understand time required to Incubate for photostability testing

How much duration of time to hold the samples in a  Photostability chamber.

ICH Defines, Expose only one batch is enough to  1.2 million lux hours(This is unlike the frequency of stability testing, eg: months 3,6,9,12.. etc)

How to convert this(1.2 million lux hr.) into time or days.

Explanation :

Lux is the unit of illumunation( )

[Lux is both singular and plural like the word "water"]

Let us assume that the intensity at particular location in the chamber for test sample is 4430 lux.

For the test sample to get exposed to 1.2 million lux hr, it has to be kept in photostability chamber for the following number of days

Y = 1.2 x 10⁶ lux hr / 4430 lux = 270.88 hr = 271 hr

Converting hours into number of days = 271 hr/24 hr = 11.29 days ~ 11.5 days.

ICH Q1B Requirement :

For confirmatory studies, samples should be exposed to light providing an overall illumination of not less than 1.2 million lux hours and an integrated near ultraviolet energy of not less than 200 watt hours/square meter to allow direct comparisons to be made between the drug substance and drug product.

FYI,

Regards,

Bujji Kanchi.