I used my Polaris meter in reflected mode to measure the brightness looking into the viewer lens (without slide). EV mode (for 100 ASA) was used for convenience. Each full EV is one stop brighter/dimmer.
| Viewer | Light Source | Power Source | Estimated Voltage | Measured EV (100 ISO) | Notes |
| Dr. T. Red Button | 2.5V 0.8A non-frosted halogen bulb | 2 C-cells, nicad | 2.5/2.4 | 12.5/12.0 | #1 |
| My MF viewer w/ plexiglass diffuser | 3 pm summer sun | Nuclear fusion AFAIK :) | NA | 17.0 | |
| My MF viewer w/ plexiglass diffuser | Homemade light box w/ 17W compact fluorescent bulb | AC from wall outlet | NA | 13.7 | #2 |
| My MF viewer w/ plexiglass diffuser | My old attachable light box w/ two 2.5V 0.8A frosted halogen bulbs | 4 C-cells, nicad | 4.9/4.7 | 12.1/11.6 | #3 |
| My MF viewer w/o diffuser | Cabin Light Panel | internal 4 AAA's, nicad | 4.8V | 11.5 | #4 |
| My MF viewer w/o diffuser | Cabin Light Panel | external 4 C-cells, nicad | 4.7V | 11.2 | #5 |
| My MF viewer w/o diffuser | Cabin Light Panel | external 4 C-cells, alkaline | 5.5V | 12.3 | #6 |
| My MF viewer w/o diffuser | Cabin Light Panel | external 5 C-cells, nicad | 6.1V | 12.5 | #7 |
Note #1: Nicads have a slightly higher output voltage (1.25V) when fully charged. Thus the bulb will be brighter for the first little while when using recently charged cells. After a short while the voltage drops to 1.2V per cell which remains very constant until fully discharged. The two brightness readings are for full charged and mid-discharged cells.Note #2: My homemade light box lighting isn't completly even. The reading is for the brightest central part. The bulb claims to be "warm" colour and it does appear close to normal tungsten. But it photographs with a strong green cast.
Note #3: The bulbs are wired in series to reduce the total current. The voltage at the bulbs is slightly reduced (0.1V) by the resistance of the 3 foot 18 gauge cable to the pack and due to a microswitch used to turn off the lights when set down.
Note #4: The AAA nicads I used were partially discharged, thus 1.2V per cell. The Cabin Light Panel requires one or two minutes to come up to full brightness. The readings were repeatedly taken until stable.
Note #5: The C-cell nicads were mid-discharge too. The voltage to the Panel is reduced by the 3' cable (no switch in this config. though). Thus the brightness is slightly lower than with the four AAA nicads.
Note #6: I didn't have four new alkaline C-cells. So 2 new and two mid (1.4V open circuit) life cells were used.
Note #7: I measured 6.2V at the pack from a mixture of fresh and mid life nicads. I extimate the voltage at the Panel as 6.1V.
Summary: The Cabin Light Panel is acceptably bright with various battery types and voltages from 4.8V and up. With 6 volts it seems quite bright when used indoors. Outdoors the diffuser towards the sun would work better, but I removed it from my viewer because it lost about 1 EV of light.
Current Draw and Battery Life: My old attachable light box drew 0.8A from the ~1.8Ah C-cell nicads. Thus battery life is over 2 hours before recharge with the life extended by the setdown switch.
The Cabin Light Panel is rated at 2.7W at 6V and I measure a current of 0.26A at 4.8V. Thus with a 6 volt battery the current will be 0.45A, so a C-cell pack will last about 4 hours. A set down switch is not advisable due to the warm up time before full brightness. Using an 800mAh AA pack the life will still be an acceptable 1.8 hours before recharge.
Using a 4 nicad cell pack (4.8V) the current is 0.26A so a C-cell pack will last 6.9 hours. With the AA pack it will last 3 hours.
The rated life with AAA alkalines is 2.5 hours. Current AAA nicads are rated at 250 mAh so they should last nearly an hour. Acceptable most of the time. I did a test with some old (> 3 years) but still working 180 mAh AAA nicads. They lasted 34 minutes (0.57 hours). Not great but if you had one or two sets of the newer 250 mAh AAA's you would be fine (if the lower brightness from 4.8V is acceptable).
I had a 5 cell nicad AA nicad pack made ($25 CDN for 950 mAh) and will add a switch to run from four cells when a lower brightness is acceptable (indoors at night). Using readily available 700mAh nicads the life will be from 1.5 to 2.7 hours. Using my 950 mAh cells the operating time will be 2.1 hours to 3.6 hours. Much longer than any single day use I normally would have. More info.
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Email: greg.erker@home.com
