I was away from work because of illness. My doctor then told me I can now return to light work. Does the Injury and Sickness Allowance end when I return to work?

Injury and Sickness Allowance is paid to those who do not receive pay because they are undergoing treatment and are unable to work. For this reason, payment of the allowance will generally cease if you are able to work and earn pay, even if you can perform only light work.
In certain cases, you may be deemed unable to work if you perform light work differing significantly from your regular duties on a temporary basis for rehabilitation work or for work on a trial basis.
(Even in such cases, you will not be paid Injury and Sickness Allowance for days for which you are paid.)
You must satisfy a number of conditions to receive Injury and Sickness Allowance in such cases. For example, you must be working under doctor's orders, the light work you perform must clearly differ from your regular duties, and the numbers of days and hours you work must generally be appropriate for rehabilitation purposes. For details, please contact your employer or the Health Insurance Society in advance.