Well scanning the literature was not helpful on this issue. It appears Olympus didn't even address it. The closest thing they had was to turn on the AF illuminator. While this would work well for subjects past 2ft it won't help your macro at all. Since I'm new to the UW world I'm not sure how this will translate into success or failure but here's some of the things my wife and I discovered toying around with settings and light. The following is all done with the camera at F8 with a shutterspeed of 1/500, RAW format, Manual Mode
1. Depressing the shutter button halfway "woke" the display up briefly in low light conditions (indoors, no lights on, window blinds closed) good enough to see the subject and take a picture. This gives you about a 1.5 seconds snapshot of what you're seeing. The action can be repeated as often as you like but the subsequent windows are shorter (1 second) because the camera doesn't have to focus. BTW...the darkened display condition is present even at F2.8 and a shutter speed of 1/100 in low light conditions. As you increase either the aperture or shutter speed it slowly dims to blackout.
2. darker conditions - subject visible by ambient light to the eye but the camera LCD is black. We simulated this with some "black out" window blinds we purchased several years ago. Since I don't have a light meter, my description will have to do. By turning on the AF illuminator (above water) the camera does an adequate job of lighting up the subject beyond 2ft and taking a picture. Personally, I'm not sure how well this illuminator will work below the surface.
In summary, its hard to quantify this exactly without a light meter; however, I would think that this will work fine for the type of recreational diving I do. Long live 40 for 40! Night dives, and/or dives with vis under 40ft would probably require some sort of permanent light (light cannon?) to be used in place of one, or both of your strobes. I'm not sure how practical that is. In most low-light conditions the camera should be able to give enough of a look (1 second snapshot) at your subject to capture the moment even in macro mode. Is it enough? I'm not experienced enough to say one way or the other but toying with this problem at your local dealer should help you decide. Had I known this before I purchased this camera I probably would have went with another choice. My plans are to call Olympus on Monday to see what my options are. I'm wondering if the SP-500 suffers the same fate.
Just a wierd item of note...the LCD only lightens and darkens dramatically in the manual mode. Every other mode S, A, Auto etc the LDC has mild fluctuations based on available light but nothing as dramatic as manual mode. Furthermore, the duplicate settings in auto and manual reveal drastically different LCD pictures. One other item of note, when you depress the shutter button halfway in any other mode the LCD holds the brightness until you either snap a picture or let go of the button. The manual mode is the only mode where the LCD only brightens momentarily and then darkens again. The only way to momentarily brighten the display (ie see what you're actually taking a picture of) is to let go of the button and press it again. Something leads me to believe its just a setting in manual mode but nothing I can find in playing with it or reading the manual is helping me.