"These bridges are made from natural light that I pump in from the surface. If you rubbed your cheek on one, it would be like standing outside with the sun shining on your face. It would also set your hair on fire, so don't actually do it."
The Aperture Science Hard Light Bridge (also called Hard-Light Surface) is a testing element in Portal 2 that is used throughout the Aperture Science Enrichment Center. Hard Light Bridges are semi-translucent solids made from natural sunlight beamed in from the surface. As its name suggests, it acts as a bridge to the player, usually allowing them to cross Goo to reach inaccessible areas. Bridges can be emitted horizontally or vertically depending on the position of its emitter. Horizontal bridges act as a bridge for the player to walk on while vertical bridges act as a shield for the player. (such as blocking Turrets) Just like Excursion Funnels and Thermal Discouragement Beams, Hard Light Bridges can be extended through the use of portals. Although the bridge is made of light, if one portion of the bridge is blocked by a solid object, the rest of the bridge will not continue as a beam of light normally would. Hard Light Bridges can be coated with gels, allowing players to use gels in places where it normally would just fall through. Atlas and P-body must utilize this method in order to complete chambers of the fifth and sixth co-op courses. (in particular, Test Chamber 03 from Course 5 and Test Chamber 04 from Course 6) Gels placed on Hard Light Bridges, however, are not permanent and will disappear the moment the bridge dissipitates or moves to a different location.
In the cooperative campaign of Portal 2, Atlas and P-body are sent to the Hard Light Bridge Factory in the Hard-Light Surfaces Testing Course. In the factory, it is revealed that the bridges, like the Turrets, are required to pass a quality monitoring before they can be put into testing. To achieve this, each emitter is attached to a support beam in a lineup, as the quality and strength of the surface is tested against a concrete wall.
Drop your co-op partner in goo while they are gesturing by removing the bridge under them
25G (B)
In any of the levels with Hard Light Bridge and Goo present (majority in Course 3), drop your co-op partner in Goo when they are gesturing by removing the bridge under them. Usage of the timer is recommended.
The Thermal Discouragement Beam is unaffected by Hard Light Bridges, meaning that it can still pass through it.
According to the Hard Light Bridge elevator video (as seen here), the light used to create the bridges are absorbed through vast farm fields, then filtered to create the bridges. The field shown in this video resembles the field Chell is sent to at the end of the game. Also in the same video, theres a small white house in the middle of the field.
The Hard Light Bridge appears to be opaque to Turrets. Unlike glass, turrets do not appear to recognize the player if the player stands behind one; however, since the turrets appear to aim with infrared lasers, it could be argued that the light from the bridge interferes with a turret's ability to detect targets (as both are very close on the electromagnetic spectrum).
When standing near the bridge in the single-player campaign, Cara Mia can be heard playing slowly about 30 seconds into the audio file.