All About Light
From Fermilab — classical, relativistic and quantum descriptions of light.

Optics
lecture notes for a Physics course on Optics, Texas A&M University

Visual Optics
From the Department of Applied Physics at The Royal Institute of Technology, Stockholm

OpticsNotes
Resources, references, and tutorial information about Optics and Photonics

The LED FAQ Pages
Lots of info on how to use Light Emitting Diodes, including many related links.

Edmund Industrial Optics
Large, comprehensive inventory of Optical Components

BES Optics
Precision and commercial optics from fused silica, fused quartz, color filters, optical glass, and other optical materials

Präzisions Glas & Optik
German source for Optical Glass products and Optical Coatings

Lighting Resource
“An online reference library for the lighting industry...including indoor, outdoor, commercial, residential and industrial lighting fixtures”

Lighting Research Center
“Advancing the effective use of Light for Society and the Environment”, Rensselaer Polytechnic Institute

Lumiram
incandescent and halogen full spectrum light bulbs (I've used these for years, they make regular incandescents look sickly yellow by comparison)

Solatube
“capture sunlight on your rooftop, redirect it down a highly reflective shaft, then diffuse it throughout your interior space”

Tubular Skylights
“transfer natural sunlight by using a clear dome over a reflective shaft which ends at your ceiling with a sealed diffuser”

LiTraCon
Light transmitting concrete!

Off-Grid Lighting Technologies
Comparison of lighting technologies available for use off the grid

Light up the World foundation
Assisting people in the developing world to obtain affordable, safe, and environmentally friendly LED based home lighting powered by renewable energy sources.

Eye Resources on the Internet
Large list of links to eye-related resources, compiled on behalf of the Association of Vision Science Librarians

The Effects of Visible Light & UVR Upon the Visual System
Overview of the potentially negative effects of visible and ultraviolet light on one’s visual health, from the Review of Optometry online.

Protection Against Exposure to Ultraviolet Radiation
How to protect yourself from the potentially harmful effects of exposure to ultraviolet (UV) radiation, from the World Health Organization

Non-Coherent Light Source Safety
How to protect your eyes from light sources such as Lamps, Plasma sources and Heat sources.

Sunglasses
“Results from a dozen studies over the last 10 years suggest that long hours in the sun without proper eye protection increase your chances of developing eye disease”

Light Pollution
Satellite monitoring of the artificial night sky brightness and the stellar visibility