How does one regulate light in the house/room for an elderly person?

Points to consider:

what will the light be used for? E.g. reading, mobilising, washing, dressing, cooking, eating, background etc.

what kind of light is it? E.g. natural daylight from a window, strong sunlight, fluorescent light, low energy electric lightbulbs, incandescent bulbs, spotlighting, strip lighting, etc.

will the older person be operating any appliances independently, or is s/he not able to do that? - if not, why not, and are there any adaptive technologies which might help? E.g. touch-base lamps, voice commands, clap commands etc.

apart from light sources, what other equipment might be used to adjust light levels? E.g. blinds, shades, curtains, rheostats, automatic nightlights, timers, etc.

if the person is not independently mobile, how will you ensure that the light around him/her is appropriate? E.g. the person is not left sitting in front of a south-facing window in summer, the person can turn off a reading light if s/he wants to take a nap, etc. etc. etc.

Hope these ideas help you make a start.

Stop by your local Home Depot and ask the person in lighting what options are available. There are several ways to adjust lighting. It may sound silly but I've found their employees to be quite knowledgeable.

by night you can get a small light (led) that opens/closes automatically...(Walmart have them).
For brighter light you can set a system with a controlled switch...

Do you mean, how do you go about ensuring a room is properly lighted, and that light levels are adjustable; or do you mean what legislation or regulations should be put in place to govern standards in older people's accommodation?

And what the blazes is "an elderly"?