oil light at idle

If I put 10w-30in my boat this would happen to me. I don't use variable viscosity oil in my boat. I use a straight 40w. If you like the 30w just try a straight 30w. 10psi @ idol seems kinda low.

My '84 doesn't have a light, just a guage. Mine runs around 10 psi at idle. While cruising, I'm around 40-50 psi. The only way I get 60 psi is close to full throttle. I used to be concerned but I read in a Ford rebuild manual that 10 psi increase for every 1000 rpm is to be expected.
My friend's father was an automobile mechanic in the 70s and early 80s. He said Fords don't have good oil pressure. I'm not sure if it's because of the oil pump or if the holes the oil flows through are bigger than most so the pressure isn't as high (volume vs pressure). I'll ask him next time I see him.
Is there any way to adjust the sensitivity on the light? Try using 20w50 oil.

I live in Central Texas and use the boat year-round. I've never used a straight 30 or 40 weight; I've always used blended oil. I've started using Rotella 15w40 Diesel Engine oil. Before that, I used Castrol 20w50. I think the sticker on my valve cover recommends 20w50. I think straight 30 is too light. I'd go with 20w50.

Thanks guys. Think I've got the problem solved. Went to 10w40 and also replaced the teflon thread seal on the sending unit with a conductive, anti-sieze. I believe the teflon was effecting the ground, thus giving false readings. been out 2x's now and the idle psi remains above 20 and the loaded pressure remains steady above 50. One of the two seems to have corrected this issue. Have fun!