Assuming that the special light and chair were bought in response to a disability or medical condition they are likely to have been reasonable adjustments made by your employer. 

A reasonable adjustment is an adjustment brought in by an employer that aims to alleviate substantial disadvantages experienced by disabled employees. It can take the form of a change to a policy, a change to the working environment or the provision of additional equipment and support. See more information on reasonable adjustments

If the pandemic has led to you having to work from home, and the absence of your chair and light is making your job substantially more difficult as a result of your autism,  you should ask your employer to buy these for you. You should make this request in writing and set out the nature of your disability and that you need the light and chair to prevent you from being substantially disadvantaged by having to work from home.  

Your employer will need to assess whether your request is reasonable given all the circumstances. See our section on reasonable adjustments and employer duties

If the request is reasonable, your employer should pay for the entirety of the cost of supplying you with the light and chair.

If, however, your employer refuses supply you with the light and chair their actions may constitute discrimination. In the event this takes place you should seek specialist advice as soon as possible and consider filing a grievance. Ultimately, you can take your employer to the Employment Tribunal for a failure to make reasonable adjustments. 

Our Resources section has more information about services offering legal advice on employment matters.