Painting the walls a dark color, or not painting the walls at all. A key factor in the brightness of any space is the reflectances of the surfaces. The more reflective your walls, ceiling, floor, and furnishings, the less it will cost to make the room feel bright. A can of white paint is one of the most inexpensive lighting accessories you can buy.

Closing shades or draperies to keep out daylight. (Or letting the daylight in but leaving the lights on anyway.) Daylight is free, has all of the characteristics people crave in lighting - good color rendering, changing throughout the day to improve circadian rhythms, and did I mention free? Adjust the blinds to direct glare toward the ceiling, but keep the light switch off when the sun is shining.

Not using dimmers. At certain times of day or on certain days of the year people need or want more light. At other times, less is better. Dimmers save energy and increase lighting satisfaction by giving occupants control of their spaces. They're easy to install. Do it. You'll be glad you did.

Forgetting to take advantage of warranties. Sure, we've all had bad experiences with either an LED or CFL lamp. But do your research to find a high quality product from a reputable manufacturer that meets your lighting specifications. Then hold them to their warranty. If something goes wrong, don't go elsewhere. Go back to the manufacturer and get them to fulfill their warranty. That will help them improve the products in the long run, too.

Avoiding new technology. New technology does require you to understand more about lighting and the visible spectrum. You have to watch for the right color temperature and good color rendering. Lighting quality issues aren't simple. But if you choose carefully, the energy savings will be worth the extra front-end effort.

Which lighting mistakes are you making? Which is most surprising to you?

We talk all the time about using daylight to provide free illumination in buildings. There is usually a small footnote along these lines: be careful about glare, shading is required, uncontrolled daylight can be problematic.
So I was amused to see this candy kiosk in the mall recently. Since it is located right below a skylight, they had to cover or shade all of the chocolates to keep them from melting.
Daylight is great, but for goodness sake, don't melt my chocolates!