Two weeks ago I bought a brilliant lamp for sun treatment indoors. Luckily, I no longer depend on the weather, which in winter is overcast 90% of time.
As Rishi advised, I chose a metal-halide (Hg-I) high intensity gas discharge bulb, OSRAM PowerBall HCI-T (see the
specs), 150W, NDL (neutral day light), with good, even, white spectrum. The luminous intensity of this class of bulbs is about 10 times greater than that of the conventional halogen bulbs, not to mention the old incandescent bulbs. So, my 150W bulb shines like a 1500W halogen and it really makes my room look like a bright sunny day. Also, because this lamp is very energy-efficient and does not heat, I can leave it turned on all day long, so that my eyes are more relaxed at average.
I bought the bulb bundled with the LIVAL Hawk projector (see the
specs), wide-flood (44 degrees) beam, and installed in on a ceiling track. I can move the projector and direct it where I like. The control gear is conventional, although it also ships with the full electronic control gear, I didn't want to wait for the next supply.
These are quite expensive toys. The projector is US $240, including the bulb which itself is about $40, and the 2m track and all its parts about another $40.
The following are my general impressions:
1. This projector, and all other projectors for such bulbs, look quite BIG. Mine is over 12 inches long and 11 inches wide. It was certainly not intended for home installation and I had pretty hard time convincing the salespeople that I knew what I was doing :).
2. The salesman also claimed that it's going to be too bright for a home room, but it appears to be absolutely OK for my purpose. The brilliant light casts contrasting shadows and the Snellen card looks like perfect black letters on a perfect white background.
Moreover, the light beam (44 degrees) is somewhat too narrow. If you want to flood the entire room with bright light, you may need two or three projectors. There have been also double-ended rectangular projectors with "very wide flood" beam, which I could consider as more appropriate, but I decided for the narrower spot light, because it fits better for sun treatment.
Compare with other home lights
3. The color of the light is pure white, meaning that the rest of home lights look like dingy yellowish candles. I wouldn't like to use other lights in the room while the projector is on.
4. The lamp does NOT utter any humming noise, as older gas discharge lamps I heard did, even though the control gear isn't electronic. What I do notice sometimes is that the light is slightly flickering. Not like fluorescent lamps with their nauseating 50 Hz vibration, you know, but there is a hardly noticeable shivering. I wonder if this is because the control gear is not electronic, or if it's a nature of the gas discharge .
5. The lamp does not ignite instantly and it takes about 2-3 min for the lamp to reach its working level of brightness and color. Also after turning off, it cannot be immediately turned back on. This inertia is due to the process of metal evaporation inside the inner capsule of the bulb. The lamp also lives longer if it's not turned on and off too frequently. By the way, the lifespan of this lamp is about 6 times longer that halogens.
Compare with a 500Wt halogen (on the left)
6. I've made a simple calculation and it shows that on a small distance from the lamp (about 5 inches), its luminous intensity is equal to the sun.
I don't I do stand that close to the lamp, but my feelings indicate that my calculation should be correct. It's really a very good substitute, whereas the 500W halogen project I used previously does not compare at all. The light spectrum resembles the sun also much closer. I even use the burning glass with the lamp, and it does not burn my skin :)