mystery tail light function

there is this one bulb on the topmost part of the tail light setup, above the signal and the brake lights. i've tried to turn it on, but it would not turn on even if i switch the lights on (parking, normal and high beam), emergency lights and the brakes. is it a malfunction on my part or does it have some other purpose/application?

Try shifting into reverse.

ALAN

oh yeah, how can forget about the reverse. man i feel like a dumbass. so having red lights there wouldn't be a good idea. i'm trying to do an all red light motif thing in the back.

no wait, it is the bulb above the reverse bulb, a fourth one. it is shown shining in SLR's website under the link for Shock Hoop. Here's the pic from SLR:

those shining lights are shining b/c they are reflectors only. The flash lit them up. There are no lights in that top part.

Correct
(Copy & Paste) http://www.geocities.com/x_canuk/rlight4.JPG
3 bulbs